Thursday, September 14, 2006
I returned to find a bit of rain in the gauge, 0.04", from the unsettled weather of the last several days around Tucson.
There is another Tropical Storm, Lane, in the east Pacific and NHC forecasts it to become a hurricane and to take a track similar to John. This brings it up to the tip of Baja in about five days. However, all forecasts related to John were very poor and the GFS eventually did best with its track. The GFS is forecasting the storm northward, so we'll see how it does with this one.
Wednesday, September 06, 2006
First, the morning Tucson sounding has dried some and indicates that CAPE will likely be not very great today and that what there is should develop only over the mountains. So another quiet day is likely locally here in the Tucson metro area. The sounding (Fig. 1) shows a nice example of why the LI computed at 500 mb out here can be very deceptive!
Second, an infrared satellite image at 1230 UTC this morning (Fig. 2) shows a large area of storms and disturbed weather over and south of the southern end of the GoC. The question is what is this and will it affect our weather up here in Arizona? The only sounding available this morning near to this area is Mazatlan, which indicates a very moist and unstable air mass with low level-easterly winds. The nam and gfs models forecast a strenthening cyclone at 850 mb down in this region; however, as per usual this summer, the models have very different details in their forecasts.
I'll illustrate this with the 850 mb 42-h forecasts from the nam and gfs. The nam (Fig. 3 - left) indicates a low center SW of Baja with strong southerly winds intruding far north into northwestern Arizona, i.e., a significant surge of moisture into the lower Colorado River Basin. However, the gfs (Fig. 4 - right) predicts a cyclone over the southern GoC that is totally separated from the circulation fields further north over northern Sonora and the U.S. Southwest; i.e., no hint of a moisture surge into the U.S.
The weather in Arizona the nextcouple of days will, of course, depend upon which model's forecast is closest to what happens in the real atmosphere. Both models forecast several weak short-waves at 500 mb moving across Arziona and interacting either with increased moisture (nam with significant storms and rainfall) or residual moisture (gfs with isolated and mountain storms). I guess that I'd tend toward the gfs forecasts, given the two models' performance during Hurricane John.
Sunday, September 03, 2006
Looking at satellite trends and station data, the lowest pressures are on the east side of the gulf of california...still think this one will be heading along the same direction as it is now and enter into the southern gulf and possibly up to Los Mochis area before landfall.
Pat called this one very well! Current visible loops seem to indicate that what's left of Hurricane John is making landfall now south of Guaymas. Obviously the GFDL model was far superior to the other models, and the consensus track has been consistently wrong. It is still possible that an orphan low-level circulation will jump Baja and drift out into the Pacific. But it appears that the main moisture and mid-level vorticity from John is heading across far southeast Arizona and into New Mexico.
CORRECTION TO ABOVE at 3:30 pm Labor Day - the circulation that appeared to go ashore in imagery yesterday wasn't the remnants of John. Imagery today indictes that John continues to be nearly stationary over the northern Gulf of California.
I've emphasized for several blog posts that when a TS comes directly into the Gulf the situation is much more complex than when a TS moves northwestward across the region southwest of Baja tip. This has certainly proved to be the case with John.
As for the backdoor front, the GFS model did very well (beginning last Tuesday or so) in forecasting this feature to broach the divide and come into southern Arizona. We were in the southeastern Arizona grasslands near Sonoita Friday afternoon and Saturday. By sunrise on Saturday (yesterday) the front had passed and we experienced a cool, suppressed day down there with brisk east winds. A careful look at the surface observations (and 24-h changes - an essential aspect of surface analysis in the Southwest during summer!) indicates that the front passed Tucson around 5 to 6 am yesterday morning; Casa Grande around 10 to 11 am; and Skyharbor in Phoenix between noon and 1 pm. High temperaturs yesterday east of Phoenix to Sells line were 5 to 10 F cooler than on Friday. The front appeared to stall from around Sells northward to west of Phoenix, providing a nice convergence zone that helped the development of the large MCS that occurred over south-central Arizona late yesterday afternoon and evening. This system produced a huge outflow of cool air that pushed southwest past Yuma and which came uphill across Tucson around 10:30 pm, with a shift to north-northwest winds and a jump in the dewpoint temperatures.
Storms today and tomorrow will occur where there's enough low-level heat, combined with moisture from John, to produce CAPE - mid-level temps are cooler over the north and west parts of the state, but deeper moisture is present over the south-central and southeast regions. Depending on exactly how remnants of John wander around, the models (which still have vastly different forecast scenarios) indicate that a dry-out may occur by Tuesday. Interestingly, the NAM spins another tropical system up southwest of Baja by 84 hours.
Friday, September 01, 2006
My rain gauge is at approximately 32.27 N and 110.93 W, with elevation of 2369 ft MSL.
Rainfall here in 2006 was: June = 0.50" July = 4.88" August = 1.09" Total = 6.47"
There was measurable rainfall on 27 of 92 days (that infamous 30% POP we see so often in the summer forecasts).
Heavy storms on just 4 days accounted for 65% of the summer total. Summer rainfall, rank- ordered, for last eight years at the house:
1999 - 9.41" (no records for June)
2006 - 6.47"
2000 - 6.30"
2005 - 5.43"
2003 - 4.69"
2002 - 4.15"
2001 - 2.70"
2004 - 2.44"
So, a nice wet summer here - not at all close to wettest, but much better than driest year.
This is one of the most complex and difficult situations that I can remember seeing here in the Southwest.
I have taken a very careful look at the NAM and GFS models out through 48-h; I have little confidence in any of the models or their forecasts beyond 48-h. There are strong and competing features in battle with each other during the next 48-h, as Hurricane John moves north at the same time as a very large upper-air blocking pattern sets up over the north-central U.S. While these things happen, a strong Canadian cold front moves rapidly southward down the front range of the Rockies, bringing much rain and moisture in its wake. This front back-doors into the Southwest and brings low-level winds around to the east over the eastern half of Arizona. Finally, low-level moisture surges very rapidly northward after after 24 to 30 hours. The only NWS offices discussing in their FDs the role of the cold front in determining the Holiday weekend weather are ELP and ABQ, but it seems fairly clear that the front is going to affect the evolution of events over a large part of Arizona also.
Brief summary of the models progs at 12, 30, and 48 hours follows:
12 - hours: Both models indicate light northerly winds at 850 and 700 mb. At 500 mb both models have light westerly flow over southern Arizona, with a weak anticylone south of the border. Upper-level winds are westerly, are strong and appear confluent over southern Arizona.
30 - hours: Winds at 850 mb and 700 mb continue northerly over much of southern Arizona. The cold front has pushed into southern New Mexico and is further west in NAM with stronger easterly winds. The NAM has northerly winds south to about Hermosilla; whereas, the GFS indicates the expected Gulf Surge has moved into the lower Colorado River Basin. Both models indicate moisture advection at 700 mb into southeastern Arizona from the east. At 700 to 500 mb there is a pronounced inverted trough swinging around Hurrican John and approaching the New Mexico bootheel. Increasing heights at 700 mb over west Texas act to increase the gradient and southeasterly winds to the northeast of John over much of northwestern Mexico. Upper-level winds continue strong from west but may be slightly difluent over southern Arizona. The NAM is moving John up the east side of Baja and the GFS is moving John up along the west coast of Baja.
48 - hours: At this time the two models have diverged markedly in their forecasts. The NAM has begun moving John westward, probably because of the large block to north and northeast. Moisture has surged rapidly northward as far as southern Nevada. The backdoor front has produced strong easterly winds over southeastern Arizona, but signficant moist advection continues at 700 mb from the cool side of the front. There is a weak 500 mb trough and vort max over southeastern Arizona, but 500 mb winds are strong northerly over most of the state. Upper-level flow appears divergent.
In contrast, the GFS continues moving John northward; the surge has moved far north and into the southern Great Basin. Easterly winds have increased over southeastern Arizona in lower-levels. GFS also has weak trough and vort max at 500 mb over southeastern Arizona. Upper-level flow is weaker and difluent over southeast Arizona.
So what does all this mean? It appears that through 48 hours the most signficant storms will occur Saturday afternoon and night.
Southern New Mexico appears to have most certain chance of widespread significant storms and rains. Southeastern Arizona may have a good storm event, but timing of moisture increases from John and encroachment of front from the east will be critical. If the front comes through too soon, the best activity zone will be shifted to the west and northwest. There is a good liklihood that the influx of low-level moisture will push far enough north that northwestern Arizona and southern Nevada (and nearby California) will experience signficant storms also.
As I said at the start of this ramble, things are really complex and getting the forecast right for tomorrow afternoon and night is a huge challenge! In the longer-term, the GFS continues John northward into the lower Colorado basin, carving out a weak trough to the west of the block. The magnitude of the rain event that the GFS forecasts after 48 hours is HUGE in the lower Colorado River Basin. The NAM takes John to the west and just forecasts a nice pattern for strong storms over the Southwest for several days.
Thursday, August 31, 2006
Hurricane John is moving toward southern tip of Baja as a strong Cat 3, or even a Cat 4, hurricane. Yesterday's discussion remains essentially valid. Initially, the pressure gradient at low-levels becomes cross or down the Gulf of California. The NAM actually predicts light northerly winds at 850 mb over southern Arizona tomorrow afternoon, but as John moves westward away from the tip of Baja, a rapid push of moisture up the GoC should occur, probably coming into the U.S. late Friday night. A turn toward the west sooner than NHC predicts would bring moisture northward more quickly.
On Saturday the moisture influx from John should interact with a strong back-door cold front coming westward across the Continental Divide, producing perhaps the most intense storms of the weekend.
There are too many complexities in the situation to have much forecast confidence beyond Saturday and even the details of Saturday are difficult to anticipate, since the flow may become strongly downslope in the local Tucson area.
A final possible complication to at least consider is that the GFDL model continues to predict that Hurricane John will move directly into the GoC and make landfall on the western coast of Mexico.
Wednesday, August 30, 2006
Today's morning sounding indicates about 33 mm of precipitable water and some decent CAPE, especially over mountains. There are light and variable winds to above 400 mb, so this will likely be a day when storms form on mountains and then wander around wherever their outflows take them.
On the large-scale, the pattern has been changing significantly. At 500 mb the subtropical anticyclone has shifted far southeastward over northeastern Mexico. While from 300 to 200 mb it is not clear that there even is an over-land anticyclone, except over far south Mexico. Down at 700 mb there is an anticyclone over northeastern Mexico and a weak trough extends from southwest Texas westward to northen Baja. Very moist air lies in and south of this trough, with precipitable water values greater than 50 mm.
The big weather uncertainties are what will happen from now through Labor Day. Hurricane John (click for IR image) was found to be a Cat 3 storm by NOAA aircraft early this morning. Complicating the picture is the fact that nearby TS Kristy appears to be approaching hurricane intensity also. The two storms are quite close and it is not obvious to me how they will interact. There was a large ensemble spread yesterday, with the GFDL model actually predicting John would move up the Gulf of California.
The moisture surge situation becomes complicated if a strong hurricane moves into the mouth of Gulf or near the tip of Baja. Initially, the pressure gradient becomes north-to-south with low-level winds blowing across or down the Gulf. If the storm then moves westward, its winds and associated pressure rises can trigger the northward surge of moisture, or the storm can continue northward bringing its moisture field with it into the Southwest.
The current NHC forecasts indicate John to be moving from south of the mouth of the Gulf to near the tip of Baja as a strong Cat 3 hurricane on Friday. Thus, the situation is extremely complex and the timing of a strong push of tropical air into the Southwest is very uncertain. All of this complicated by the fact a strong cold front moves rapidly down the High Plains on Saturday and Sunday, trying to back-door into southern Arizona.
All that one can do with such a difficult mix of mid-latitude and tropical features is to watch the observations very very closely. Of course, most weather attention the next few days will be on the east coast events associated with Ernesto.
Tuesday, August 29, 2006
First, there has been a classic and very pronounced surge of low-level moisture northward up the Gulf of California. Pressures at Yuma dropped quite low yesterday afternoon and the moisture surge was observed near dark between 8 and 9 pm there. The passage of the surge was quite spectacular as indicated by the changes in surface conditions from 8 to 9 pm. It has continued through the night. The NWS Doppler radar data show that the surge extends upward to just above 3000 ft MSL at Yuma this morning.
However, across southeast and south central Arizona moisture has also increased dramatically over the night due to both outflows from northern Mexico and the moist flow behind the back-door front, also mentioned yesterday. The change in the soundings at TUS from yesterday to this morning is also quite spectacular. Strong moisture increases are apparent up to 600 mb. This influx of moisture occurred during the late night and early morning hours and was more gradual than the surge observed at Yuma. Surface observations from Douglas to Tucson to Sasabe to Sells all showed significant dewpoint increases during hte night.
The morning sounding at Tucson indicates that signifcant CAPE may be present by afternoon. If the low-level moisture continues to increase, potential CAPE by afternoon could become quite large for out here. Temperatures at 500 mb have fallen and there is some steering flow from the north-northeast. Thus, it appears that an interesting and stormy afternoon is possible over southeastern Arizona.
In the longer term, Tropical Storm John developed yesterday afternoon. The NHC expects it to reach hurricane strength this morning. The forecast by NHC anticipates that John will rapidly intensify into a major hurricane and track to the northwest along a track that would, if it verifies, bring another major push of moisture into the Southwest by Friday and Saturday. All told a very interesting week and Labor Day weekend shaping up!
Monday, August 28, 2006
First, the middle and upper-level wave spinning over the northern Plains has a weak trough hanging back, east-to-west, over the western U.S. The models appear to move this feature southward across at least eastern Arizona tomorrow. There is currently cold advection with the S/W, and this would be quite favorable, especially given the very nice vertical wind shear profiles that develop during next 24-hours, for strong storms, if there low-level moisture and CAPE in place. There also appears to be an upper-level moisture plume from what was Ileana approaching the Southwest.
A gradual advection of low-level moisture is occurring across southern New Mexico and into southeastern Arizona - this is due to the back-door cold front that has coming down the Plains as it tries to push westward across the Continental Divide.
Now to the south. No observational data wrt to upper-air soundings, as per the last 7 weeks. The NAM initializes a strong inverted trough over the southern Gulf of California at 500 and 700 mb - the 700 mb trough appears to brush across southern Arizona tomorrow afternoon. This occurs about the same time the 500-300 mb weak S/W is positioned over eastern Arizona. Thus, the question is: how much of this is real and how much is happening only in the NAM world?
Satellite loops indicate that a pronounced wave is moving westward across the lower Gulf of California. So, the moisture surge predicted by the NAM may indeed be getting underway. Surface obs indicate very high dewpoints along the GoC and south winds at LaPaz and Loretto. The U 0f A GPS precipitable water time series page shows that a huge increase in precipitable water has occurred at Hermosilla during past nine hours, i.e., since midnight. Values there are almost 50 mm this morning.
So it appears that there is probably at least a 50/50 chance of everything coming together over next 24 to 36 hours to support a new round of summer thunderstorms over parts of southern Arizona. The dilemma here is that very dry air will be lurking very near. The key is likely to be tied to whether or not a GoC surge actually occurs by tomorrow morning.
Who said that summer forecasting is easy?
Sunday, August 27, 2006
I'm certainly glad that I wasn't working the midshift at NHC this morning!
The models (at least the NAM and GFS) are at best ambigous in their solutions regarding what might evolve at low latitudes the next few days. Ernesto seems to go a variety of different directions and the NAM tries to bring another tropical system up toward Baja at end of period - last time it did this it was an artifact and nothing materialized.
The NHC does anticipate that the tropical wave coming off Central America will develop into a tropical system. Meanwhile, there is something sitting over the southern Gulf of California with considerable associated convection. It seems to be a weak, nearly stationary low, BUT with the absence of observational data over much of Mexico continuing, the models seem constrained mostly by their last forecast.
What a mess! Does anyone care that the missing sounding data have caused extremely unreliable model forecasts for much of southwestern N.A. this summer?
Saturday, August 26, 2006
Interestingly, the TUS sounding still has a fair amount of potential CAPE, so storms continue likely over mountains to the east.
I have just checked the 12Z soundings for TUS for the last four mornings. The winds in the 600 to 400 mb layer have been west-southwest to west-northwest each of these days and precipitable water has ranged from 42.9 to this morning's 33.5 mm. One could ask:
Did the monsoon end four days ago?
What kind of storms have been occurring with baroclinic westerly winds and lingering high moisture and CAPE?
I would call these "hybrid" or "mixed flow regime" storms since they are occurring in a meteorologically mixed environment. There is a preprint article about hybrid storms at:
Interestingly, the TUS sounding still has a fair amount of potential CAPE, so storms continue likely over mountains to the east.
I have just checked the 12Z soundings for TUS for the last four mornings. The winds in the 600 to 400 mb layer have been west-southwest to west-northwest each of these days and precipitable water has ranged from 42.9 to this morning's 33.5 mm. One could ask:
Did the monsoon end four days ago?
What kind of storms have been occurring with baroclinic westerly winds and lingering high moisture and CAPE?
I would call these "hybrid" or "mixed flow regime" storms since they are occurring in a meteorologically mixed environment. There is a preprint article about hybrid storms at:
Friday, August 25, 2006
Mike and all,
Well I sure goofed yesterday by not paying attention to the outflow/mesohigh spreading southeast over us. That's of course a real kiss of death. What happens when you're trying to do too many things at once.
Today seems really a mess - westerlies with drying in top half of troposphere - how far will it mix down? No matter how I fiddle with TUS sounding in low levels, I get afternoon max theta-w of 22C and thus only a tiny sliver of CAPE.
PHX sounding looks like it should be thundering there right now - maybe a bad sounding point? Definitely some CAPE up there but stronger west winds lower down bode ill. Guess that we can say mountains should be active yet again - so what's new?
The upper-air charts show cold advection west of trof in NW U.S. at 500 and 300 mb indicating southward movement as per models' forecasts. I guess that I am not sure what a fairly strong wave like this coming south over continent in summer might actually evolve to. The first waves that have come by here have come off Pacific. A piece of the northern S/W may end up abandoned by its mother wave and wander around in the subtropical ridge after tomorrow.
NAM shows two tropical and one baroclinic 500 mb vort centers at play through the weekend - we know two are real but third?????? The GFS hints at the end of the monsoon in about 7 days - although it may be happening next couple of days. Then the GFS let's it come back in at longer periods. But the GFS doesn't seem to know about TD 5, potential hurricane Ernesto. Of course, neither of these models seems to have had much reliability for weeks.
I'm plenty confused and so, I'll just sit and watch what happens!
Thursday, August 24, 2006
The satellite precipitable water this morning seems to indicate a distinct plume of high precipitable water extending from Ileana and lower Gulf of California all the way north into the lower Colorado River Basin - see graphic by clicking below.
Note that the storms that developed in south central Arizona a bit before sunrise appeared to develop at the nose of the higher precipitable water plume.
The high dewpoint air is now just south of Las Vegas and it is not clear whether or not the plume will impact storm probabilities in southern Nevada - the midshift forecasters there expressed concerns about the possible surge in their early am forecast discussion.
Finally, the next couple of days appear fairly complex as the S/W in the northwest does battle with a strong subtropical circulation and several tropical systems.
Wednesday, August 23, 2006
However, the dilemma here is that high amounts of moisture and precipitable water are already present over much of the southwest U.S. So what impacts might be expected? I am going to guess that Ileana will result in increased moisture advecting into the lower Colorado River Basin, southern Nevada, and the southern California deserts. A distinct surface surge may be more difficult to detect, but one is certainly possible. Watch Art Douglas' surge index on the Creighton Univ. web page at:
Tuesday, August 22, 2006
There were also a couple of measured severe gusts within the PRISMS mesonet in the Phoenix metro area that are not on the report map. A brief story and photo of damage in the Tucson area yesterday is at:
Here at the house there was much thunder from nearby cells early in the afternoon, but once again only wind and sprinkles and a trace of rain. However, the evening sounding was much moistened with considerable instability in all layers below 650 mb - nighttime/early morning storms developed and it was raining here at sunrise with 0.18" in the gauge.
The morning sounding at Tucson exhibits a very nice "onion" sounding with a deep, ice saturated layer producing anvil rainfall above the onion bulb. Sounding is at:
Today appears to favor a heavy rain threat in southeast Arizona, as the inverted trough at 700 mb that brought a favorable wind profile for severe storms yesterday has moved on to the west. The western lobe of the 500 mb subtropical high is over southeastern Utah this morning, and the weak trough separating this anticyclone from the larger anticyclone over the Southern Plains appears to be between here and Phoenix. Thus, winds aloft are very light and variable up to about 300 mb and storms should be very slow moving in this part of Arizona today.
Tropical Storm Eleana is predicted to become a hurricane shortly and the NAM and NHC forecast the storm to move northwestward and to come north of 20N. Thus, this storm may come close enough to the south end of Gulf oc California to trigger yet another push of deep tropical moisture into Arizona Friday or over the weekend.
Monday, August 21, 2006
The most negative aspect of the day was the evolution of the thermodynamics during the afternoon (we knew we were dealing with a marginal wind profile). By evening, the Tucson sounding CLICK HERE showed drying had occurred during the day below 600 mb and that the afternoon BL was characterized by a moisture profile that was not well-mixed. This is a difficult negative to overcome, and the storm that made it to airport must have been propagating with a fairly strong downdraft (as the gust to 33 kt at TUS indicates).
Part 2 - Overview of conditions this morning: This morning's Tucson sounding CLICK HERE indicates moistening up to 500 mb, no residual BL is present (meaning substantial heating will be needed to build a deep BL over lower elevations), and there are fairly strong southeasterly winds present below about 650 mb (i.e., a downslope direction). Winds at upper-levels have veered again and are southwesterly around a weak trough over the West (so there is a good shear profile, except for the weak winds present from 500 to 350 mb). The key forecast issue is whether a well-mixed BL will be able to develop in the face of the downslope winds. (Mike Leuthold - let us know what the WRF model does if you can find time.)
On the larger-scale, standard level charts we find that:
At 700 mb: An anticyclone centered near Las Vegas is affecting most of Arizona, except the far southeast where the inverted trough over western Mexico appears to have resulted in southeast winds. The main anticyclone over southeast Oklahoma is separated from the western lobe (which actually has three weak centers) by a trough line extending from near Phoenix northeastward to east of Omaha. The 700 mb level is very moist at all sites upstream from Tucson (i.e., Albuquerque, El Paso, and Chihuahua MX).
At 500 mb: A western lobe of the anticyclone is centered in southern Utah, with a trough line separating it from the strong eastern anticyclone center over Oklahoma. This trough extends from near Tucson northeastward to central Nebraska. The southern part of this trough is an extension of the inverted trough over western Mexico - this trough appears to have moved westward away from the upper-level feature that has been nearly stationary for last couple of days over west Texas. Thus, the NAM may have it sort of right today, with the lower-level trough actually moving westward.
At 250 mb: The upper trough over west Texas/northeastern MX is very diffuse and hard to define - thus, this feature appears to be confined to the very upper troposphere, making it a likely non-player in the evolution of weather west of the Continental Divide. The TUTT seems very pronounced and shifted to a northerly location from central Mexico eastward across south Florida. Upper flow today is not nearly as diffluent as it was yesterday morning (a negative).
Why all this description? I think that today's 12 UTC observational data illustrate well how terribly difficult it can be to sort out all the potential interactions and evolutions of weak features which will come together to produce afternoon and evening thunderstorms. My gut says that today will be a much more active day than yesterday ended up being, but only time will tell which features dominate.
Sunday, August 20, 2006
The morning observations today - Sunday August 20 - are very interesting and indicate some potential for a tropical-like squall and significant storms this afternoon.
The morning Tucson sounding, view at:
went bonkers above 350 mb, so we have to decide whether to accept the data below 350 mb as being good. If I accept the observations below 400 mb, it appears that CAPE is substantial for out here, that there are some easterly steering winds above well-mixed BL cloud base (~700 mb), and that anvil level flow is from the southwest (favorable).
The 500 mb anticyclone has a split off a lobe right over Phoenix this morning - not a favorable position. But, there is not a deep, barotropic anticyclone aloft over Arizona.There is a deep trof/shear zone from 700 to 200 mb over New Mexico between the large anticyclone to the east and features to the west. The flow above 300 mb appears highly difluent this morning (favorable). The weak flow in middle levels continues - the storms of August 8th got organized with similar weak flow, so we'll have to see what happens today.
The models at 0600 UTC provide little help - NAM continues with the near TS it has somehow genertaed off to the SSW. Thus, one has little feel for how much credance to give the predicted wind profiles. In general, the wind patterns predicted by GFS for this evening are less favorable than what's observed this morning.
Certainly should be a much more interesting day than have been the last couple of days, since the early morning deluge of Wednesday the 16th.
Sunday, August 13, 2006
The NAM has had terrible initializations for most of the last week with a semi permanent strong inverted trough in various random parts of northern Mexico. The result of this is that mid level forcast winds have been much stronger (up to 30kts) that what has actually happened, and these winds then caused storms in the model to organize and propagate into the lower elevations, which hasn't happened. The NWS had bit at these poor forecasts more than once with high pops for low elevations and even a mention by SPC sometime last week that the forecast shear was high.This is a link to a model sounding over Mt Lemmon made from the 12z NAM from the previous day (6 Aug).
This is the actual sounding.
Perhaps the NWS should put some effort and money into supporting northern Mexico soundings during the summer. The above cases show how poor the models perform when there are no soundings from there. It would be money well spent.
The frequency of various wind directions during the "monsoon period" (i.e., the period with PW values consistently 30mm or greater) are shown in the table below:
* Note - 2006 data are through August 10th
It is clear that the observed wind directions, within the 600 to 400 mb layer, during the last three summer "monsoon periods" have been highly variable. If wind directions from the SSW to ESE are considered to be typical or favorable "monsoonal flow," then only 36% of the days at Tucson have exhibited "monsoonal" wind directions.
Interestingly, if the wind directions for all days shown in the table are averaged, the resultant mean wind direction during the monsoon periods was from the southeast. This is because the SW and NE winds essentially average to SE, and the result is not an accurate picture of what wind directions actually were during the three summers.
Indeed, these summer wind directions are not at all persistent. Although Tucson experiences a summer period characterized by high PW and significant thunderstorms and rains, the variable wind directions lead one to ask whether Tucson actually experiences a summer monsoon.
CLICK HERE -- for Monsoon Variable Comparison figures discussed above
Some of the most severe storms to strike the Tucson metro area occurred during the late afternoon of Tuesday August 8th. The synoptic setting was not one that seemed supportive of such intense storms. These storms displayed a distinct linear organization for about two hours as they moved across the southern half of the city. Some details and a photo are at this newspaper url:
Later this summer or Fall I will analyze the most severe events of the summer and contrast them with a newspaper description of what meteorological conditions bring Tucson the most severe storms during the summer.
Finally, the almost total lack of sounding data from much of Mexico since early July continues to frustrate attempts to analyze the larger-scale conditions over southwestern North America - the negative impacts on the models have been especially significant.
Monday, August 07, 2006
The overnight increase of precipitable water at Hermosilla, MX, was quite spectacular - as per Pat Holbrook's comments last evening. The following is a link to the GPS precipitable water time series at U of A atmospheric science.
Thunderstorms moved into central and south Tucson last evening with thunder and light rain observed at Davis Monthan AFB and light rain (but no thunder or lightning) observed at NWS TUS. Lightning was clearly visible from our house but apparently no showers up here in the north metro.
The morning soundings at Tucson, Phoenix, and Yuma are quite different from each other.
CLICK HERE to see the 12z soundings for these 3 locations.
Both Phoenix and Tucson, with heating, have the most potential CAPE observed since the 25th of July. The winds are very light at Tucson above 800 mb, indicating a good potential for heavy rainstorms and possible hail over higher elevations. In contrast, Phoenix has a strongly veering wind profile that would favor strong storms and possible severe wind gusts - however, the Phoenix wind profile should trend toward that of Tucson. Phoenix may also be vulnerable to low-level drying, since drier air is very close to the west. Definitely a difficult forecast situation at Phoenix!
In contrast, Yuma has strong veering winds but remains very dry and stable. I still expect a dramatic low-level moisture increase at Yuma, as the air sample by GPS at Hermosilla moves northward into Arizona.
It will be interesting to see how things evolve today.
Sunday, August 06, 2006
The warm, dry air aloft that came in from the south on Friday really shut things down, since it eliminated what CAPE there had been. It was a nice example of how things here in southern Arizona can go totally suppressed, even though low-levels remained fairly moist. The situation was also interesting since the NAM runs on Friday kept showing precip here every 6 hour period through Saturday night. The NAM has been forecasting cyclones and waves south of Tucson for a number of days, but today is first day that observations show much. It's not clear whether there is any cooler mid-level air lurking over Mexico - there have been almost no soundings over much of Mexico since the third week of July. This may be the reason that the NAM initializations and forecasts have been so unreliable of late.
So, we'll see what tonight and tomorrow bring.
Thursday, August 03, 2006
There were significant MCSs over Arizona from the 25/26 through the 30/31. On some days there were MCSs early over the mountains and then later over lower elevations.
The episode began with a great northward push of low-level moisture into the state that was triggered by TS Emilia moving through the favored area southwest of Baja (see earlier post). I had anticipated this surge would reach Arizona 12 to 18 hours earlier than it did. I put too much confidence in the early track forecasts of NHC, which were too fast. Art Douglas warned me that he didn't think the TS would move northward as fast as the early NHC forecasts indicated and he was correct.
The first MCS event occurred during the night of the 25th (26th UTC time - note that Arizona is on MST and that midnight is 0700 UTC). An earlier post covers this first event in some detail.
Satellite IR images are shown for UTC times on the 26th through the 1st of August.
CLICK HERE for Figures 1 -8
As the week progressed, the large-scale pattern evolved from one dominated by a large, middle-level anticyclone over the west, i.e., a fairly typical July setting into one with a cyclone and several associated short-waves spinning over northeast Arizona and western New Mexico, remaining nearly stationary for a couple of days.
MCSs during the period first moved toward the west-southwest, and then toward the south, and eventually toward the southeast.
The rain events measured at our house are shown below - and, for a larger perspective total CG counts over the Arizona domain (domain has been shown in earlier posts). My 24-h rain measurements were taken around 1300 UTC each day and the 24-h CG counts ended at 1200 UTC each day.
Date / Rain Total / AZ CGs
7-26 / 0.14" / 36,256
7-27 / 0.17" / 26,696
7-28 / 0.39" / 14,614
7-29 / 1.64" / 25,047
7-30 / 0.40" / 10,013
7-31 / 1.39" / 14,907
8-01 / 0.15" / 5,652
Total rain measured here at the house was 4.19"! The most unusual aspect of these heavy rains, at least here locally, was that approximately 80% of the rain occurred between 2 am and 8 am local time. Thus, events in southeast Arizona for the week considered were mostly nocturnal and more like the summer rainfall climatology of Omaha than of Tucson.
More will follow.
Monday, July 31, 2006
P.S. For you flood-o-philes out there, July 31st is also the 3oth anniversary of the Big Thompson Flood in Colorado which took place 7-31-1976.
Sunday, July 30, 2006
"Perhaps the pops are an artifact in the forecast as the NWS does more important things than update the 60 % to 100%. Any idiot can see its raining."
I understand that the NWS does far more important things than generate routine forecasts for the next seven days. I also understand that, to NWS management at many levels, getting the mundane products out on time seems to be almost as important as getting a warning out before a life-threatening event occurs. If I ran a weather service, the emphasis would always be on getting the immediate and critical products out to the users and customers. I would also have a "caution sign" posted and broadcast for the customers stating: "Because of current severe and/or life-threatening weather, production of routine products has been temporarily suspended. Routine services will resume when the current threat has ended."
"Effort spent updating the forecast, possibly taking away resources from some other, more important task in the NWS office would be foolish."
I agree. In fact, while I was writing the post that was commented on, the forecast staff at the Tucson office had recovered from the early am crises and were amending the morning forecast. They were willing to amend, probably since the window view was obviously different from the forecast, and tackle all the onerous grid-modification work required of a first period forecast change. Kudos to them!
But, I do have a much longer-term concern about weather conditions and the first period forecast, or short-term forecast or whatever, being obviously out of sync. I have observed this situation far too often, in far too many places, and in far too many kinds of weather situation not to feel very bothered about the overall situation.
"Furthermore, even if the NWS did update the forecast, many media outlets would continue to read the old forecast. They don't check for updates every time it is read."
This isn't a generic aspect of the media. One thing that has disturbed me deeply over the years is to listen to media ridicule the NWS because a forecast has obviously gone awry, as per: "That's the forecast! Don't those guys have a window over there?" Heard on the radio in Norman, OK, on a morning when the forecast was for sunny but the skies were heavily overcast.
"You are worrying about things that simply don't matter when there is actual life threatening flooding occurring. I fail to see how your commentary on this matter is at all productive?"
I agree again, but think that the NWS offices should make it very clear to its customers when the focus has shifted away from the standard routine, and I think NWS management should support its line staff to decide when routine procedures and products should be dropped temporarily, as per my thoughts above.
Friday, July 28, 2006
Another nocturnal MCS moved across southeastern Arizona early this morning. Lightning and thunder here at the house around 2 to 3 am with 24 hour rainfall of 0.39" (0.06" of that occurred before noon yesterday morning). Lightning and thunder at Davis Monthan AFB around same time but, as is typical, no significant convective weather was observed at Tucson International Airport.
The Rillito wash has been running bank-to-bank during past 24 hours, as have most washes - stupid motorists water rafting in SUVs and other typical craziness that attends heavy storms down here abounds.
Thursday, July 27, 2006
Driving in to the university, in steady light to moderate rain, I heard the following forecast on NPR for the Tucson area.
Today: Mostly cloudy. Numerous showers and thunderstorms early in the morning...then scattered showers and thunderstorms. Highs 87 to 92. West wind 5 to 15 mph. Chance of precipitation 60 percent.
This is still the forecast at 9:30 am for the Tucson metro area, even though it has been raining across the metro area since 1200 UTC. The NPR forecast was followed by news about the roads that are currently closed due to flooding washes. The observations at TUS (verification point for the forecast) since 1200 UTC have been:
Day Time VSBY WX 1hr precip
27 Jul 8:55 am 10.00 -RA 0.02
27 Jul 7:55 am 10.00 -RA 0.04
27 Jul 7:30 am 3.00 RA
27 Jul 6:55 am 10.00 -RA T
27 Jul 5:55 am 10.00 -RA 0.01
27 Jul 5:10 am 10.00 -RA
27 Jul 4:55 am 10.00 -RA 0.07
Perhaps the POPs mean that when the current rain stops, then there will be a 60% chance of more rain later today?
Or, perhaps I just don't understand how the NWS defines and uses POPs anymore.
I've attached several images: CLICK HERE
Fig 1 - IR image 0200 Z 26 Jul - This image shows three distinct MCSs, at least in the satellite view, that would force new convective development as their gust fronts converged over Phoenix.
Fig 2 - IR image 0630 Z 26 Jul - This image shows the resultant, huge cold cloud shield covering much of Arizona. The interesting thing about this MCS is that radar views indicate that 3 or 4 distinct smaller MCS are propagating a variety of directions beneath the over-arching anvil cloud. One of these actually moved eastward from the Phoenix Valley up into the Salt River drainage.
Fig 3 - A map of CG lightning strikes from 12z 25 Jul to 12z 26 Jul. The CG locations are color-coded by time. Close examination of the timing of the CGs also indicates the different propagation movements beneath the cirrus.
Thus, this was a conglomerate MCS with much internal sub-structure and no long-lasting leading edge convection, or consistent motion due to propagation. This event appears somewhat similar to what Blanchard (Bull. Amer. Meteor. Soc., 71, 994-1005) terms a "chaotic MCS," see for example his Fig. 6.
Fig 4 - IR image 12Z 27 Jul - This image shows a sunrise MCS that developed near midnight last night just ahead of a distinct 500 mb circulation moving southwestward within the larger- scale anticyclone that is over the Southwest. It is almost as impressive as the MCS on Tuesday night. This MCS, however, did exhibit leading convection/trailing stratiform through much of its life and has also propagated steadily toward the southwest. A pleasant morning surprise to find light rain falling and rain in the gauge again (0.17" is all). As the MCS came overhead, no thunder or lightning was observed at TUS - in marked contrast to the observations at David Monthan AFB, and also at our house.
Fig 5 - Catalinas photo at 1300Z 27 Jul - view of the Catalinas taken through light rain at about 6am this morning.
Yet another interesting day, thanks to the great moisture surge produced by Tropical Storm Emilia on Monday night.
Wednesday, July 26, 2006
While the atmosphere was very unstable for convection, the winds were quite light below 500 mb and there were no distinct steering flows, nor much in the way of wind shear within the lower half of the cloud-bearing layer.
Storms developed over high terrain in three regions: 1) east to south of Tucson and 2) north to northwest of Phoenix during mid to late afternoon, and then 3) northeast of Tucson/east of Phoenix during the evening. The three resultant MCSs produced outflows that converged into the Phoenix area shortly after dark.
The MCS south of Tucson was characterized by storm cells that seemed to move randomly in a variety of directions, before eventually drifting to the west. Some of these produced hail - see http://www.azstarnet.com/allheadlines/139451
The late MCS (number 3) produced a great lightning show between 9 amd 11 pm here in Tucson, but, alas, not much rainfall.
A final, congolmerate MCS formed directly over Phoenix as the gust fronts converged there, produced torrential rains, and drifted slowly westward during the night.
Outflows from the massive convective episode did not reach to Yuma. Because of the slow movements and lack of a long-lived, dominant outflow driving westward propagation, I would not call this event a tropical-like squall or desert derecho.
I took four photos - CLICK HERE - from the house. Two of these show my rain gauge at noon yesterday and then at sunrise this morning. The third photo shows a dusty outflow moving north across the Catlina Mountains toward Phoenix late afternoon yesterday, and the last shows stratus cloud along the flanks of the mountains this morning.
The PHX and TUS soundings are quite stabilized this morning from all the activity yesterday. The Tucson area can usually recover more quickly than can Phoenix - this should be especially true for this event, since rain amounts around Tucson were not great (0.14" here at house, Trace at both TUS and DMA).
My initial impression is that neither the NAM nor WRF forecasts forecast the complex evolutions of storm complexes that actually occurred.
More later on this event!
Tuesday, July 25, 2006
Monday's reports - Phoenix had a high of 114F with a late evening, high-based thunderstorm producing wind, dust, and a trace; Yuma had a high of 114F with no rainfall; and Tucson had a high of 108F with yet another day of very suppressed convection.
The good news is that moist, low-level air surged into most of southern Arizona during the night. So, temperatures will moderate some but at the cost of higher humidities. I think all of us here in southern Arizona hope that the higher humidities will bring increased storms and rain!
Sunday, July 23, 2006
I've posted three images - CLICK HERE - the first shows IR imagery of Emilia at 2030 UTC on the 23rd, the second shows IR imagery of Emilia at 0100 UTC on the 24th, and the third shows the current NHC forecast for Emilia. I've highlighted, in light green, what I consider to be the critical region that a tropical system must move through to trigger a northward surge of moisture up the Gulf of California. The latest IR image shows that Emilia has an eye and that it is approaching this critical region. Current observations from La Paz and Mazatlan indicate that such a surge may have already begun at the south end of the Gulf. Operational forecast models are usually very slow in their forecasts of such an event.
I expect that a surge of high dewpoint air will likely arrive at Yuma, Arizona, as soon as 1400 UTC tomorrow morning (and if not by then, within the ensuing 12 hours). The surge event triggered by Emilia will be hard to differentiate clearly from the outflows likely from two significant MCSs that are also moving over the Gulf of California this evening - see the most recent IR satellite image.
Regardless, it appears that the next couple of days will be far more interesting than the past several!
Saturday, July 22, 2006
Friday, July 21, 2006
Initially, there is a figure on the web page that shows annual thunderstorm days observed at TUS versus annual thunderstorm days observed at Davis Monthan AFB (DMA). Note that TUS and DMA are spatially separated by only about 8 km.
CLICK HERE to view the figure of thunderstorm days per year for 2001-2005.
This figure leads to an obvious, and very important, question: What happened after 2001?
This topic continues that posted on the blog earlier as: "Where have all the thunderstorms gone?"
More to come.
Thursday, July 20, 2006
My point here is - Since the 1970s, I have always felt that if we can't accurately tell the public what's happening right now, why would we expect them to have much confidence in our forecasts. My first rants on this subject were made after I was driving into Boulder in heavy wet snow (about 3 to 4 inches had accumulated already in Louisville, Colorado) on my early morning commute. The official NWS forecast playing on the radio was for rain and thundershowers, possibly turning to snow by evening. This experience in Colorado happened on a May morning almost 30 years ago, and by the time the event ended I measured 34 inches of snow accumulation in my back yard.
We were in Phoenix most of the day and during our drive back we saw and experienced some very wild weather. Car thermometer was registering 114F as we left Phoenix. As we were approaching Picacho Peak, a strong tstm cell off the north end of the Picacho Mountains threw out a macro burst/haboob that moved from northeast toward the southwest. When we got to this duster the visby was only down to 1 to 2 miles across the interstate. However, a very intense storm somewhere to south of Marana, over the Avra Valley, produced a huge haboob - CLICK HERE to see two photos we took as the dust cloud approached, also shown is a web cam photo of one of the storm cells over north Tucson at 5 pm MST. The haboob photos were taken at about 4:20 pm near Red Rock, Arizona, from the shoulder of I-10. Visby went to zero for a short period; wind gusts from the south were in the range 40 to 60 mph; there was chaos on the interstate; and there was a five car pile-up just down the way from us. During trip back to Tucson temperature ranged from 114F on south side of Phoenix to 76F just north of Tucson. Only 0.10" in the rain gauge here at house. But, I guess that I should leave town more often, since my presence seems to be a strong suppressant!
Tuesday, July 18, 2006
Sunday, July 16, 2006
What happened with such an outwardly "good" situation? The primary bugaboo seems to have been that the approaching sysnoptic scale system was strong enough to "override" the diurnal boundary layer flow regime, bringing pronounced downslope, drying, boundary layer winds to southeastern Arizona. Note that terrain elevations decrease from over 7,000 ft msl at the Continental Divide in southwestern New Mexico to about 2,500 ft msl in Tucson area.
In some ways yesterday was somewhat similar to events aassociated with TS Nora several years ago - much precipitation expected but none realized due to the strong east winds in low-levels. Interestingly, Nora is often referred to locally as "No rain at all."
I hope to post a numbe r of graphics and more discussion about July 15th later today.
Saturday, July 15, 2006
What went wrong: First, I made a novice kind of mistake by finalizing my outlook before all the observations were available. (Note that I forecast mostly using the basic observations and then may use model progs to cross check details of what I'm anticipating.) Yesterday's morning sounding that eventually arrived from Phoenix NWS/SRP showed a considerably drier lower-half of the atmosphere than did Tucson's and that advective winds were pointed toward Tucson. So, during the day that deep layer of moisture that was sampled by the TUS morning sounding gradually vanished, particularly between 700 to 500 mb. Thus, much of the day in southeast Arizona was markedly suppressed. It's not an irrelevant question to ask: "Where did that low-level moisture sampled by the Tucson sounding go?"
However, storms erupted near dark, producing a great lightning event, and I see there were a couple of severe reports around 10 pm. Two small MCSs raced west-southwestward during the night, so the outlook was not a total bust.
Looks like the drying we suffered yesterday was advecting from the higher terrain to north/northeast and mixing down - evening soundings at PHX and TUS were much different than in the morning. The TUS evening sounding remained very unstable but needed substantial mesoscale kick to lift moist part of BL air to LFC. (The 00Z TUS sounding shows an excellent example of how very strange boundary layer structures can sometimes evolve out here.) Davis Monthan AFB and TUS international airport both got measurable (TUS 0.30") and DM had gusts to 52 mph - lightning show was spectacular from the house with lots of thunder - note that once again a storm went right over the TUS airport and there was no tstm observed there (one TUS ob had the added remark "distant lightning SE-SW"). Not even a trace here, as is so often the case.
Next couple of days will be dominated by the huge, upper-tropospheric cyclone that's coming westward across northern MX (note there were a couple of impressive MCSs moving westward from TX Panhandle into NM last evening!). Our big day better be today - there's substantial cooling below 500 mb and lots of upper-level moisture coming with this not-at-all-subtle system. So I expect some substantial changes while we're under the influence of this large-scale system.
I note the following in the TUS morning forecast - POPs go to 40% for tonight and tomorrow night but are 30% for all other periods for next 7 days - high temps are forecast in the range 99 - 108F for entire 7 days with today and tomorrow being hottest (today 103 to 108 and tomorrow 100 to 105). I suspect that we may well deviate much more from climatology than this forecast does.
Should be another couple of interesting weather days!
Friday, July 14, 2006
Today, Friday July 14, appears to have all the ingredients coming together for a newsworthy significant thunderstorm day over southeast and south Arizona. Significant moisture and CAPE remain in place; steering level winds are from east to east-southeast at 15 to 20 kt; upper-level winds are from the north so that anvils should spread off to left and behind any organized storms that develop; middle-level temps have cooled about 3 to 5 degrees; BL temps will be very hot encouraging strong outflows; and finally the wind profile has the potential to support tropical-like squall line/MCS moving toward the west. I anticipate a much more interesting day today and will keep my digital camera handy!
Thursday, July 13, 2006
For the past week: no surge events July 6 - 9. Surge events with values in range of 10 to 20 have occurred on July 10, 11, and 12..
The slow increase in moisture has lead to a situation over southern Arizona where high values of CAPE have developed at the same time that boundary layer temperatures have increased. The TUS sounding this morning is quite potent, but the winds aloft are weak. There is likely to be a dramatic increase in storms today, despite the NWS current POPs of zero for the local Tucson area.
Tuesday, July 11, 2006
About a year and a half ago I circulated an e-mail commenting on the dramatic decrease in thunderstorm events that had occurred in the official NWS current weather observations at Tucson International Airport since 2001. A number of people in NOAA and other organizations expressed concern, but the observations seem not to have improved at all. I feel that inaccurate current weather observations at TUS constitute a real and serious threat to aviation operations. Of course, the climatology of thunderstorm events at TUS has been badly distorted also.
I have just taken a look at the July 2006 observations to date at both TUS and also at DMA (Davis Monthan AFB). These two surface observation sites are separated by only about 8 km. During the first 10 days of July the current weather observations at TUS indicated that two thunderstorms had occurred at the airport, while the observations at DMA indicated that nine different thunderstorms had occurred at the air force observing site. Thunder was reported on two different days at TUS but was reported on six different days at DMA.
Perhaps the most interesting observation at TUS this month occurred when rainshowers with gusts to 51 mph and visibility of 2.5 miles (in HAZE!) were reported on the Fourth. During the same period at the nearby AFB, a thunderstorm was observed continuously for well over two hours.
I will be gradually preparing a paper focused on this topic at the new website that Katie and I are setting up. I will link to the paper from the blog as figures and expanded background are posted on the website.
It's the kind of thing that one might ask an intro class: "How many things can you find wrong on this page?" The focus on cold fronts is interesting, since most of us would love to have some really good cold fronts come by during our summer heat!
As for the box at lower right "This week's forecast:" I had no precipitation at my house (sadly one of the driest locales in the metro area) on "Today" - June 28th, but did hear thunder from a storm on the Catalina Mountains. On Thursday, Friday, and Saturday I observed both thunder and precipitation at the house.
Monday, July 10, 2006
Sunday, July 09, 2006
The following link is to a newspaper story covering the event. Embedded in the story is a link to a slide show of storm-related photos taken on Friday.
Thursday, July 06, 2006
The new WSR-88D doppler radar system has been operating nationwide for more than a decade. The radar processing systems routinely produce maps of radar-estimated precipitation accumulations.
The CG lightning strike detection system has been operating nationwide for about two decades.
The satellite observing systems have been in place, and continuously improving, since the early 1970s. Satellite rain estimation techniques have been used by researchers and the NWS for more than two and a half decades.
It seems clear that the NWS could draw upon observations from these systems to define better the onset of the monsoon.
But, the larger question is: Why doesn't the NWS use data and products from any of these systems (systems whose cost to the nation has been at least in the tens of billions of dollars) to verify, assess, or crtically evaluate their forecast products?
For example, the SPC could routinely use CG lightning strike data to evaluate the reliability of their thunderstorm outlooks.
Satellite and radar products could be used to evaluate what actually happens relative to point weather observations and etc. etc.
If anyone knows more on these issues, please share your information with us.
Note - now that I've thought about it a bit more, it seems that the NHC might make more quantitative use of the satellite data in assessing their forecasts than other components of the NWS.
Sunday, July 02, 2006
I guess that we should have specified some ground rules for the blog. Public discussion, regardless of the topic, is not very effective if we don't know who is talking to whom. This, of course, is why newspapers and magazines don't publish letters unless they are signed.
I don't know how things work in the general blogger world, but MadWeather will not accept unsigned posts in the future. We will leave the current "anonymous" post up on the blog, since we had not addressed this issue before it was posted.
I would suggest, if someone has comments but doesn't want to identify themselves, that you contact me directly.
Saturday, July 01, 2006
Using the NWS Tucson definition for the official start of the monsoon, it appears that the monsoon arrived at Davis-Monthan Air Force Base one day earlier than it did at TUS. These two surface observing stations are less than 10 km apart.
If one used other definitions of the "start" of the monsoon, the dates of arrival would vary considerably.
For example, if the start at TUS were defined as the first time that the running three-day average surface dewpoint temperature exceed 50F, then the monsoon would have begun on 6 June.
If we defined the start of the monsoon in Arizona as the first day on which the count of cloud-to-ground lightning strikes across Arizona exceeded 10,000 (a fairly significant number of strikes!), then the 2006 monsoon would have begun on 8 June.
Enough said about the Arizona monsoon conundrum for summer 2006!
Wednesday, June 28, 2006
We are also establishing a complementary webpage - this will allow postings of a more technical nature, including draft scientific papers. Some of these will hopefully be submitted to the Electronic Journal of Severe Storm Meteorology. Don't know about this publication media? Click on the ejssm link available on the blog links list for details. Regardless, we will announce the new webpage as soon as it is functional and has some content.
Monday - June 26, 2006
Clouds and more Clouds
Moisture building now may bring early monsoon
Did you like the weather Sunday night? Mother Nature is expected to provide an encore every night this week, complete with high winds and possible rain.
Meteorologists believe the monsoon may even start this week.
'We're getting close,' said -----, a National Weather Service meteorologist in Tucson. 'Moisture is going to be increasing over the next couple of days.'
Up to 4,000 customers lost power during Sunday's storm, with electricity restored overnight.
Tuesday - June 27, 2006
Signs say summer monsoon not yet upon us
It looks like it, it feels like it, but trust us - and if not us, the National Weather Service - the
monsoon has not yet begun.
For the monsoon to officially start the dew point must average 54 degrees on each of three
consecutive days, says -----, a meteorologist with the National Weather Service
'We've hit 54 several times in the past few days, but we haven't averaged 54 yet on any given day,' -----said.
The average dew point Monday was 52 degrees.
We'll be watching.
Tuesday, June 27, 2006
concerning the weather in Arizona during the first week of June.
The tough question: "Are these storms the start of the Arizona monsoon or summer rainy season?" has already become an issue for the general public and the media in Arizona, and thereby also an issue for the NWS, and perhaps private forecast services. This question arises almost every year, but usually more toward the end of June or early part of July.
The weather: For the past week in Arizona (June 1- 7) there have been thunderstorms, lightning, rains, winds, some hail, some severe storms, and even two severe thunderstorm watches.
The synoptic pattern: Beginning a week ago, the pattern over the southwest US and northern Mexico became characterized by a strong anticyclone from 700 to 250 mb that has meandered around Arizona and the four-corners region. The high has now shifted eastward and is forecast by the models to relocate southward, toward a more typical position for mid-June. The flow pattern has been essentially a summer flow pattern with easterly to southerly winds aloft over southeastern Arizona. There has been enough moisture embedded with the flow, plus really serious moisture recycling from the rains, for there to be boundary layer CAPE somewhere in the state most every day for the past week.
I've posted a June 6th satellite image (FIGURE 1) three upper-air charts (FIGURE 2 for June 4th, FIGURE 3 for June 2nd, and FIGURE 4 for June 7th ) along with a Tucson sounding for June 6th (FIGURE 5). Also posted is a map for June 6th showing lightning CG strikes to ground for the day (FIGURE 6).
What's a monsoon: The meteorological definition is that it is a distinct seasonal shift in the prevailing wind direction - usually the wind shift referred to is that of the surface wind. However, surface winds in this part of the world are typically dominated by diurnal flows generated by the complex orography, i.e., high elevation mountains in close proximity to low elevation desert. Thus, the average surface winds at Tucson are similar in July to those in January. So, we are forced to look aloft to find seasonal shifts from westerly winds to easterly winds. Note that clouds, rains, dewpoint temperatures, and other weather phenomena associated with a monsoon are not part of the meteorological definition of a monsoon.
Persistence: Arizona and parts of northern Mexico are far enough north that monsoonal flow regimes come and go during the summer as troughs in the middle and upper-level westerlies sometimes push across this region. These intrusions of the westerlies often produce "breaks" in the monsoon by bringing in drier, convectively stable, air from the eastern Pacific. However, the overland portion of the middle-level, subtropical high is usually located far enough north to result in average wind directions (300 to 600 mb) over much of Arizona during summer that are distinctly shifted from winter directions. The situation here in Arizona is thus one where periods of monsoonal flow develop intermittently from late spring through early fall, with the length of periods of monsoonal flow becoming longer during the second half of July and August. The occurrence of a summer monsoon is much better defined and persistent over portions of central and southern Mexico (the reason that Douglas et al. called it the Mexican monsoon).
Subtropical low-level moisture: During early periods of monsoon flow each year low-level moisture content (e.g., surface dewpoints) is not high. Often the only CAPE that develops during early monsoonal flow regimes is over the mountains, leading to high-based "dry" thunderstorms and the great wild fire dangers of late spring and early summer. By the middle of July, subtropical moisture, with much higher surface dewpoints and total precipitable water, has usually shifted northward, affecting much of central and southern Arizona. Swamp coolers become ineffective (they weren't doing such a great job here the last two days either!), storm bases lower, CAPE increases, and the heavily raining storms of summer occur.
The confusion: Much of the general public doesn't understand that the monsoon flow regime comes and goes. They want a yes/no answer regarding whether the monsoon has started or not. Unfortunately, there is no meteorological on/off switch at higher latitudes affected by the Mexican monsoon. Monsoon flow regimes are intermittent, the storms and high humidity are not a continuous daily phenomena. This has apparently led the public, and sometimes the media, to often refer to individual intense thunderstorms as "monsoons." As per, "Boy, that was some monsoon that hit us yesterday!"
The NWS yes/no definition: Since the public wants a yes/no answer, the NWS has developed a simple definition of the start of the monsoon. Here in Tucson there must be three consecutive days with daily average dewpoints of 54F or higher. The start of the monsoon is then declared to have occurred on the first of these three days. So, there is always a three day period of uncertainty before the NWS says, "Yes, the monsoon has "officially" started." (Note that Phoenix uses the same definition but with the threshold dewpoint being 55F.) The NWS at Phoenix and Tucson declares the start of the monsoon to have occurred based on observations at two points, leaving those interested in the weather in other parts of Arizona wondering whether the monsoon has "officially" started at their home yet.
Since there will usually be thunderstorms and rain within monsoonal flow patterns before the "official" onset of the monsoon, it is no surprise that confusion is unavoidable.
Monsoon or not: Finally, after all this long-winded background, my answer to this question. The storms of the last week have been, in my opinion, "monsoon storms" since they occurred in an unusually early, summer, monsoonal flow pattern. We'll experience a return to more normal westerly flow, and hot dry weather, before the monsoonal flow returns again. But, we've had a refreshing and interesting early start of our summer rainy season.
Monday, June 05, 2006
There's been a lot of talk and media articles about the SE Arizona storms of early June and whether or not they might signal the start of an unusually early monsoon. Let's look at this from a synoptic viewpoint . . . but first let's talk about what exactly is the monsoon in Arizona. My next post will address the storms of early June.
Sunday, June 04, 2006
I am establishing a weather blog so that I can comment on issues of weather interest here in the Southwest, and sometimes other places. Stay tuned for future postings. One of the benefits of being retired is that I can be a "free range" commentator on a variety of things that I think I know at least a smidgen about. During the coming summer I hope to address things like:
- The mystery of why there are about half as many thunderstorms observed in Tucson now as there were 5 to 10 years ago
- Conditions that lead to organized MCSs in Arizona
- The value, or lack thereof, of weather forecasts that call for climatological conditions and POPs each of the next 5 to 7 days
- The usefulness of seven-day forecasts in general
- Gulf of California moisture surges
- Whatever else might catch my attention.
This will be an "invited participant" blog, once we figure out how to get this component functional. When we do, all who have been alerted of the blog will be invited to contribute their opinions, comments, etc., when so moved.
Please feel free to "advertise" this blog to others who might be interested.