Saturday, October 25, 2008
FYI - I have posted an article
"Strongly Superadiabatic Lapse Rates Aloft at Six Upper-Air Sounding Sites"
coauthored with Barry Schwartz at:
We have examined data for two years of RRS soundings and compared with data from earlier sondes. This quantitative comparison indicates a very serious decline in the quality of the upper-air data is occurring because of the use of the new Sippican GPS microsondes by the NWS.
Thursday, August 21, 2008
AJ makes a very good point here and one that serves to emphasize how difficult the forecast challenge is for the coming 84 hours. The three principal models each have different solutions, and we have little in the way of observational data to help evaluate the model initializations, since the key features analyzed by the models are within a great data void.
First, if one looks at the NAM, the GFS, and the ECMWF model runs from this morning – which I hadn’t when I wrote the original blurb – it is clear that each of the three models has somewhat different solutions for the initial conditions.
As per at 500mb:
The GFS analyzes an IT from south of GoC into north central MX where it connects with a trailing trough from the S/W over the central Missouri River Basin.
The ECMWF has this feature analyzed further north, extending from the south central GoC to SE Kansas.
The NAM is similar to the ECMWF except that it has several additional vorticity maxima further south and southeast which neither of the global models have.
We do know that such a feature is present and that at 12Z this morning it extended from Nebraska south-southwestward entering Mexico in the western Big Bend country.
Each model goes it own way in the forecast fields. The most important issue relates to whether or not there is a feature in the actual atmosphere that is going to spinup into a tropical system off Baja. Only the NAM indicates this evolution. The NAM solution would result in a very deep intrusion of subtropical moisture into the Southwest. At this time we mostly know that there has been ongoing convection in the regions where the NAM forecasts tropical development.
Both the GFS and ECMWF strengthen the inverted trough over north central Mexico and forecast this as the main feature that affects southern Arizona on Saturday and Sunday. The GFS stalls this feature over north central Mexico, while the ECMWF is more aggressive and keeps it further north and moving westward. The wind shear profile forecast on Sunday by the GFS is not nearly as favorable for organized storms (assuming that the key ingredients of moisture and CAPE have moved/developed north of the border). The ECMWF is probably in between the two other models wrt wind shear.
Current IR and water vapor satellite imagery indicate that the feature over north central Mexico has a clear circulation now and that it is moving westward. Significant convection is developing ahead of this feature over the Sierra Madre Occidental.
So where does all this lead? The forecast situation appears even more complicated than what I originally wrote. The most likely scenario for the next 84 hours is not at all clear at this time, and the evolving situation merits careful monitoring.
Pressures have fallen and are quite low over the interior Southwest and may drop another couple of mb over the next 36 hours. There is also a weak inverted trough over the lower end of the GoC that has widespread convection associated with it. As this first disturbance shifts westward, there should be a low-level surge of moisture back into the lower Colorado River Basin. This moisture surge could begin as early as morning tomorrow but should be quite pronounced by mid-day Saturday.
The NAM forecasts that a tropical storm will develop just southwest of the tip of Baja and this feature, if it materializes, would deepen the moisture inflow to Arizona on Sunday and Monday. The NAM also forecasts very favorable wind shear profiles for organized convective storms in southeastern AZ both on Saturday and Sunday afternoons. Thus, both days could be very active if there is CAPE available.
It appears that the crucial aspect of the weekend synoptic setting will the temperatures in the middle levels. If the very warm air to the north and northwest spreads over southern Arizona and northern Mexico there would be little CAPE to realize, and it would likely be fighting an inversion aloft. However, if the easterly flow that develops at 500 mb has a fetch from the central and southern Plains by Saturday afternoon, the 500 mb temperatures would be much cooler and supportive of storms.
I think that the more favorable situation will evolve and, depending on the details, either Saturday or Sunday afternoon and evening should be quite active with strong and organized storms.
Saturday, August 16, 2008
Thursday, August 07, 2008
"When it rains it usually pours, but sometimes it just spits."
Sunday, August 03, 2008
So what went wrong - I think that it was mainly related to the dry air in the upper-troposphere curling across southeast Arizona and keeping there from being much activity to the east - as per the WRF forecast. Although there were more storms to the east than the WRF indicated, they were not widespread and didn't produce any significant, organized outflows. With the GoC surge and increasing low-level moisture, the Tucson sounding at 00Z yesterday afternoon had substantial CAPE, but needed mesoscale convergence to kick it loose. That didn't happen.
As for today - moisture is way up as expected and there is substantial CAPE at both TUS and PHX this morning. El Paso is fairly stable so we have to assume that the air over the southeastern mountains is somewhat like the Tucson sounding. Morning wind shear from middle to upper levels is unidirectional but the NAM indicates that the wind profiles may improve by evening. Mainly a shear zone affecting southeast Arizona today and with no data from the south, it is hard to have much confidence in the model predicted winds aloft. So, there will be a lot of small and mesoscale interactions driving the evolution of storms today - good potential for more severe across all of southern Arizona and Phoenix could get hit by a strong, severe storm event. The chances are probably better for here at house today, but, even though it's not a binary call like yesterday, the shear profile could throw anvils over this part of town. So it's wait and see, as per many to most storm days down here.
The other wild card at play here is that there is a lot of strong morning storm activity out to the west of Tucson. If these storms continue to build produce early, cool outflows, that would complicate things greatly. I got a couple photos as sunrise showers moved by, producing an early morning rainbow. I'll post these to the blog later today.
Saturday, August 02, 2008
Hot boundary layer temps and pocket of cooler 500 mb air, plus slight increase in moisture allowed storms, particularly at higher elevations, to overcome the strong inversion near 400 mb. Rain reported at 23 of the 91 Alert gauges in eastern Pima County - again mostly in mountains and foothills - the 1.50" at Agua Calienta Park seems an outlier, but there was spectacular lightning off that way. One wind damage report out at Pinal Airpark. Afternoon cells did not seem to have much in the way of precip shafts but then things obviously changed before dark.
Here at house - lightning, thunder and brief spit of rain shortly after 9 pm.
Situation today is very difficult with a number of competing plus and minuses.
Very dry air to east in NM
Morning soundings continue with marginal IPW and boundary layer moisture.
Best difluence ahead of approaching upper-level, inverted trough appears to remain south of border.
Upper-level winds weak as we remain near the center of upper anticyclone.
Cool pocket at 500 mb has moved on to our west and northwest.
Nice push of subtropical moisture occurring into lower Colorado Basin, with some signature in PHX am sounding and Yuma VAD showing the influx to be about 4,000 ft deep. GPS IPW shows nice increases at the stations around the northern GoC.
Outflows from MCS over Mexico last night have pushed Td up across all of southern AZ and helped the GoC surge along.
Tropical low spinning off Baja in good location to keep low-level moisture flow going for a couple of days.
Very nice steering winds for storms that will tend to leave anvils to rear of strong cells.
Approaching inverted trough that extends down to 700 mb.
Summary - Looks good for strong storms with likely tropical squall line organization and somesevere storms and heavier rains, but today or tomorrow? I think things will come together today better than one might expect and that afternoon and evening should have strong storms - tomorrow will of course be highly affected by what does or does not happen during the next 12 hours. Chance of rain here at house probably at least 50% this evening.
Friday, August 01, 2008
Art's photos can be viewed directly at
Thursday, July 31, 2008
This morning there are, however, some indications of changes underway that will bring storms back into this part of the state. This morning there were quite a few ACC drifting around beneath the cirrus at sunrise. Since there has been no NWS sounding taken at TWC the last two sounding times, I have to guess about what a sounding here would look like this morning. There does appear to be some increase in east-northeasterly winds around 500 mb, along with some cooler temps advecting over southeastern Arizona today. Deep, subtropical moisture remains south of Hermosilla, but hot surface temps, along with the cooler middle level temps indicate that high-based storms should return to some of the sky island mountains of southeast Arizona late today, producing some lightning and gusty outflows.
The widespread convective activity over the southern half of GoC, coupled with falling pressures in the lower Colorado Basin, as well as the 500 mb wave moving slowly westward across the lower GoC all are good indicators that a northward push of the subtropical air is imminent. My guess is that we should see a push of low-level moisture into southwest and south central Arizona within 24 to 48 hours, followed by increasing storm activity for the next few days.
Monday, July 28, 2008
The sounding indicates IPW of 1.65" and the SPC analysis of this sounding indicates a forecast CAPE this afternoon of 1180 J/Kg. However, the GPS IPW from FSL indicates that precipitable water is probably between 1.3 to 1.4" - the difference between the sounding value and the GPS value being more than 0.25" - a huge difference and one that could seriously affect the convective forecast. See:
Note that the Td increases substantially between the surface value and the first level of sonde data - this aspect of the TWC soundings has been noted off and on - particularly on calm mornings - for the past several weeks. The Td values from the sonde then decrease nearly linearly to 715 mb, even though the sonde was passing through two elevated, residual boundary layers. The Td trace does not appear to be physically realistic and is probably too wet in each of the residual layers. Thus, I conclude that the Td data are bad and that the atmospere's dewpoint structure is quite different than that measured by the RRS sonde.
The reasons for the questionable data are not clear - but two possibilities come to mind - 1) local conditions on the roof of the NWS building may be affecting the first couple of data points and 2) the RRS sonde humidity sensor for this flight had a slow response time for Td and did not properly respond to Td changes below about 715 mb.
So, one is left wondering exactly what the local conditions might actually have been at the time of the sounding. So it goes.
Thursday, July 24, 2008
Low-level moisture has been sloshing around in different ways last night and this early morning, with decreases in the southeast from the east; increases in south central Arizona from the southeast; and increases in lower Colorado Basin due to weak surge which should continue and increase in strength and depth. Diurnal wind regime may return today in the Tucson area, which would increase the low-level moisture.
Entire forecast problem is acerbated by the TWC sounding which is apparently about 7.5 mm too wet this morning. I am guessing the bad data are at and below 850 mb and modifying the sounding accordingly. My estimated sounding for this afternoon has boundary layer well-mixed moisture at 10 g/kg and cloud bases at 650 mb. This gives moderate CAPE with only slight CIN above, assuming no further drying from east.
At 500 mb a weak inverted trof extends from the north end of GoC to SE Colorado, with some cooler air on the east side of this feature. At 200 mb a strong inverted trof extends from west of Albuquerque, south between El Paso and Tucson and into the vast Mexican data void. This setup gives the Tucson area good steering level flow this late afternoon, but little vertical shear. If storms organize along outflows, they could move westward faster than their anvils.
NAM model indicates better wind profiles tomorrow. Thus, good potential for organized and some severe storms either this afternoon or tomorrow, with the answer hiding in the devilish, smaller-scale details.
Tuesday, July 22, 2008
Conditions remain very moist this morning; however, the TWC sounding is about 5mm too high in IPW according to the FSL comparison site. The 12Z sounding is quite strange, exhibiting the off-the-surface moist spike that Mike Leuthold pointed out about a week ago. Many of the 12Z soundings for last several weeks show this same artifact - particularly on calm mornings. This morning's sounding exhibits an adiabatic layer off the surface and then a sharp inversion to about 890 mb. This same layer has the strange Td structures. These data in lowest levels probably reflect the local conditions on the roof of the NWS building, and the moisture spike may result from similar contamination.
Regardless, moist and unstable and a calm troposphere again this morning. Only 11 of the Pima County Alert gauges had precip yesterday - making it the driest day since last Friday - with the significant amounts being on the mountains. The amount of anvil that the early mountain storms produced was truly amazing, but of course left all the lower elevations under thick anvil for much of the afternoon. Looks like anvils will tend to spread toward south and southwest today also.
Upper-level difluence increases this afternoon and evening as the inverted upper trof approaches. This feature directly affects southeastern Arizona tomorrow afternoon and steering level winds finally pick up. The 500 mb temperatures with this feature are -8 to -9C, i.e., very much cooler than have been observed at TWC for many days!
The best vertical shear for organized, propagating MCSs is forecast by the NAM on Thursday afternoon/evening as the winds at high levels - 200 mb - turn to south-southwest as remnants of Dolly approach the Big Bend. Wind shear predicted by the NAM remains very favorable on Friday afternoon. Very difficult to call which day will bring the most intense storms to southeast Arizona for rest of week, since local and small scale features and the previous day's events will be playing a big role each day. But it will be very interesting to observe what actually evolves.
It can be found under BLOG IMAGE GALLERY Weather Summary for July 18-20
We've also added some other July storm photos here, including lightning photos from near El Paso. these were provided by Mike Hardiman.
Monday, July 21, 2008
Madweather post: Weather Summary Last Three Days - July 18 through 20
This morning conditions over most of Arizona remain very moist and the TWC morning sounding (Fig. 1 - link below) indicates a subtropical air mass with just over 50 mm of IPW. Although there is abundant CAPE, the winds aloft are light and variable through most of the troposphere. Thus, the situation is much like yesterday when there were many storms which remained mostly over higher elevations. The large subtropical anticyclone at 500 mb has three distinct sub-centers. The main one is over Arkansas with weaker centers in the west over southeastern Arizona and southwestern Wyoming (see Fig. 2).
The most interesting aspects of this morning's charts and the model forecasts relate to what will occur on Wednesday through Friday. There is a strong upper-tropospheric shear zone at 200 mb from somewhere near the southern end of the Gulf of California that extends east-northeast through the Mexican data void, and then across southeast Texas and southern Arkansas. The NAM initializes this feature a bit to the north and weaker than it appears to be. The NAM forecasts the west end of this feature to become a distinct upper-cyclone that moves westward across northern Mexico on Wednesday and Thursday. As this occurs, the 500 mb steering flow becomes east-northeast. The flow at 200 mb becomes more diffluent, initially from the east-northeast on Wednesday and then from the southeast on Thursday. Thus, a more favorable shear profile returns for propagating and organized storms.
Figure 1 Figure 2 Figure 3
It then appears that the remnants of TS/Hurricane Dolly (see Fig. 3) will affect southern Arizona on Friday and perhaps Saturday. Currently, the models and NHC forecast Dolly to follow a track similar to that of Claudette during the period July 8-17th in 2003. All-in-all it should be an interesting weather week.
Monday, July 07, 2008
Yesterday was the day with the most widespread rains. A large are of heavy cloud at sunrise acted to suppress local storm development. But shortly after dark outflow winds converged over Tucson, helped by two weak short waves - one from the southeast and one from the northwest - triggering a large MCS. Every one of the Flood Districts 91 gauges reported measurable rainfall except for three - which I suspect may be out of order. Largest accumulation was 2.60 at White Tail on the Catalinas. Here at the house we had 0.60".
Today the two middle-level waves continue to interact and the atmosphere is very wet with high IPW amounts. The widespread rains will mean a shallow boundary layer later today that will need strong outflows into lower elevations if storms are to develop away from the mountains. The longer range forecasts continue with very wet forecasts out past 7 days as both depression Five-E and an upper cyclone over eastern Mexico move slowly this way and continue the flow of subtropical moisture into the Southwest US.
Some summaries for the past seven days:
Douglas Tstms on the 1st, 3rd, 5th, and 6th total rainfall 0.17"
Art Douglas reports storms and rain at Ash Canyon (just south of Sierra Vista)
on the 2nd through the 5th (and probably yesterday also) with rainfall of 1.00"
Nogales: Tstms every day with total rainfall 1.31"
Tucson (TUS) Tstms on 1st, 3rd, 4th, 5th, and 6th total rainfall 0.45"
Here at house Tstms on 1st, 3rd, 4th, 5th, and 6th total rainfall 1.39"
Phoenix (PHX) Tstms on the 3rd and 4th total rainfall only a Trace
Note that Phoenix has had high temps of over 105F every day of this period and that 3 days were over 110F. While temps were over 100F in the afternoons the dewpoints were often in the middle 50s to low 60s. Thus, the heat stress and misery gradient between Tucson and Phoenix this last week has been very strong, probably maximizing between Picacho Peak and Casa Grande.
Saturday, July 05, 2008
Obviously, it's not very technical, but here is my attempt at a definition.
Subjective - if it is spitting rain, you can almost run between the drops.
More quantitative - if you observe spitting rain falling onto a porous surface, such as concrete or flagstone, you'll note the following. The drop splats and wet spots remain separate from one another while it is spitting rain. If the surface becomes completely wetted, then light rain, or heavier, has begun.
So that's it - not copyrighted; feel free to use.
Watch a video (Madweather's first attempt at doing this!)
A strong cluster of storms near Green Valley produced a deep outflow that was visible on the KEMX base scans. It passed TUS at 6:46 pm when winds shifted to the south with gusts to 38 mph. Thunderstorms were developing along this outflow as it moved north across the city. We had thunder and light to moderate rain here at house from about 7:00 to 7:40 pm with total rainfall of 0.35". The lightning was quite spectacular with CG bolts jumping out to the north of the cells through clear sky. Quite a dangerous situation.
Significant moisture remains in place but winds aloft over southeastern Arizona are becoming nearly light and variable in the NAM forecasts through midnight. My guess is that this afternoon's well-mixed, in moisture, boundary layer will have theta w of about 24C - a very favorable value for moderate CAPE and heavy storms. But the situation will probably be like yesterday and the air mass over the deserts will require a good kick from outflows from storms at higher elevations. Timing will depend on heating and how quickly storms develop over higher elevations. Also appears as if the northwestern half of state will have an active day.
Friday, July 04, 2008
Yesterday was a very active day with most reporting stations in southeast and south central reporting thunderstorms and wind gusts of 30 mph or greater. Douglas reported a gust to 75 mph, and others of note were: 53 at Mt. Hopkins RAWS, 45 at Scottsdale airport, and 44 at TUS. The Pima Flood Control District monitors rainfall at 91 sites in eastern Pima County and 56 of these sites reported measurable rain for the 24 hours ending at 6 am this morning. Notable amounts: 4.61" at Manning Camp in the Rincons (this is from a RAWS site and may be suspect) and 1.77" at Oracle Ranger Station. The most rain reported in the main part of the City was 0.47" at Pantano and Houghton. Of the 18 City gauges only 6 reported measurable rain, showing that the higher elevations did much better. Here at the house we had lots of lightning and thunder, several outflows and a couple of brief spits of rain, amounting to a trace. But the cool outflows and strong smell of rain made for a great evening.
This morning the moisture contents over southern Arizona have continued to increase. The TWC sounding is very moist and indicates the most CAPE present for the season so far. The IPW products and surface observations show that the surge of GoC moisture which began midday on Wednesday has pushed north almost to Las Vegas. IPW at Tucson is 38 mm this morning and Phoenix has 41 mm.
Winds in the upper and lower troposphere are light and variable, but steering level winds from 400 to 600 mb are from the east-northeast at 15 to 30 kts. There are no synoptic features of note today, except for the moderate wind flow around the midlevel anticyclone and perhaps a bit of midlevel cool advection. Expect that it will be another active day across much of southern Arizona. With higher moisture and lower cloud bases, the threat of heavy rain is greater today and the possibility of severe downbursts remains significant. The increased CAPE will allow better propagation of mountain storms into the deserts during the afternoon and evening.
So, another active day likely with lightning fireworks for the Fourth.
Thursday, July 03, 2008
Low-level moisture has continued to push into the lower elevations of all of southern Arizona during the night. Moisture increases and southeasterly winds are most spectacular over the lower Colorado River basin as per Yuma surface observations, the KYUX Doppler velocities (See Figure 1 and Figure 2) and the GOES IPW (Figure 3). Winds at 1500 UTC this morning are gusting 20 to 30 kts at Yuma and the dewpoint has risen into the lower 70s. The VAD shown in Figure 2 indicates that the surge of GoC air may bextend up to 4,000 ft AGL.
The Tucson 1200 UTC sounding this morning shows a slight increase of low-level moisture and is a bit dry relative to GPS IPW. There is a very deep residual boundary layer from yesterday and some CAPE indicated over low elevations, with CAPE over the higher mountains likely to be quite substantial. This afternoon's CAPE at lower elevations will be determined by how the low level moisture is advected by low-level winds, any further increase in moisture, and also by any warming that might occur between 500 and 400 mb - so estimating desert CAPE is toughest aspect of this afternoon's forecast.
Steering winds are likely to be northeast to east at 20 to 25 kts around 0000 UTC, while upper-level winds will blow the anvils off to the southeast - an excellent shear configuration for severe thunderstorms in southeastern Arizona. With diurnal afternoon low-level winds from the west-northwest, the shear profile below 500 mb will be supportive of strong, mesoscale outflows.
The threat for severe macroburst winds today is high, and depending on how the CAPE evolves there may also be some heavy rains in lower elevations and possibly hail. Hail is quite likely in higher elevations.
All-in-all looks like a good setup for a significant thunderstorm day here in southeast Arizona and also in much of the Southwest. As is often the case here in southeast Arizona, the outlook for tomorrow will be strongly impacted by how convection evolves late today and tonight - the NAM indicates even more activity tomorrow but this could be impacted by strong outflows later today and tonight. An interesting 4th regardless.
Sunday, June 29, 2008
For the past week or so there have been daily thunderstorms over southeast, and sometimes central, Arizona. Moisture values and CAPE have generally remained marginal with IPW values of around 25 mm. Thursday afternoon (the 26th) IPW increased briefly above 30 mm and there was ample CAPE over lower elevations of southeast Arizona for severe storms and heavy rains to occur in the Tucson metro area. The street flooding here on the north side of town was quite impressive, even though at the house there was only 0.33" of rainfall. Temperatures in middle levels have remained quite cool through this period, with temps at 500 mb of -8 to -10 C, and thus there has been CAPE around even though moisture values were low.
On Thursday the high, subtropical values of IPW (>37.5 mm) had inched northward toward the end of the GoC and the borderlands. This morning the subtropical moisture has retreated southward and covers only about the southern third of the GoC.
This morning the Tucson sounding indicates that there will probably be CAPE present this afternoon at lower elevations in southeastern AZ. If we end up with 4 g/kg in the well-mixed boundary layer (BL) there will be slight CAPE, but it looks like the value could be 5 g/kg or even greater. Steering-level winds are easterly at about 20kt. There is a weak upper-level SW over New Mexico and the NAM forecasts part of this feature to move southwestward and interact with the northern end of a quite pronounced tropical wave. So the potential for storms appears enhanced today, especially given that 500 mb temperatures remain in the -8 to -10 C range across all of the southwest. There is also pronounced westward advection of higher moisture values across southern New Mexico. By afternoon there should be substantial moisture convergence over southeastern Arizona as the afternoon diurnal northwesterly winds butt into the easterly flow from New Mexico. Thus, there appears to be high potential for a significant storm day over southeastern AZ today, with severe macrobursts likely - given the high cloud bases and very hot subcloud BL.
In the longer term it finally appears that a wave of significance will move across the lower GoC. The models indicate substantial cool advection at 700 mb with the tropical wave that is now over Mexico and indicate significant storm activity likely in Sinaloa and southern Sonora - perhaps even moving out over the GoC. It would be nice to have some sounding observations over Mexico to help one evaluate the model forecasts, but all of northern Mexico has been without upper-air data for almost a month now. The evolution and movement of the wave, as predicted by the models, as well as the cool advection and rainfall would trigger a low-level surge of high moisture values into southern Arizona sometime between early morning on Tuesday and mid-day on Wednesday.
All in all, it looks like a number of very interesting days are on tap for us here in southeastern Arizona.
Monday, June 23, 2008
The FSL time series comparison of GPS IPW versus TWC IPW since the 19th of June indicates that 5 soundings were apparently too dry, while one sounding (1200 UTC 19 June) was very wet relative to GPS IPW. See Figure 1. Careful monitoring of the remotely sensed IPW continues to be the best way to make an initial assessment of how accurate a given TWC sounding might be.
The 00Z sounding last evening (see Figure 2) indicated a deep, well-mixed boundary layer extending up to 500 mb; however, the moisture structure was quite questionable, with very dry conditions off the surface and no recovery to a well-mixed value. This led to the "dry" sounding wrt IPW.
The 12Z sounding this morning (see Figure 3) indicates a very deep residual boundary layer, but the moisture structure is extremely erratic. The IPW values correspond well. Given the unrealistic physical nature of the Td data, I suspect that the agreement of the two IPW values is essentially a coincidence this morning. If the afternoon BL mixes toward 5 g/kg, then there is a small amount of CAPE present; however, if it mixes toward 4 g/kg then there is no CAPE present. Given the erratic Td data trace it is very hard to make a subjective forecast of the late afternoon sounding.
This was probably the first significant event, for southeast Arizona, of the 2008 summer thunderstorm season. Widespread convection occurred over parts of southeast Arizona and particularly over southwest New Mexico and northern Mexico. See Figure 1.
High cloud bases and a very hot boundary layer led to an organized, mesoscale outflow that affected much of southeastern Arizona. Passage here in Tucson occurred about 4:30 pm local time. The outflow was well-depicted as a fine line on the KEMX reflectivity display see Figure 2.
Note that Douglas, Arizona, reported a severe convective gust of 51 kt at 3:32 pm local time after the haboob had moved passed. This severe storm event did not make it into SPC's list of wind events for the 21st.
We were returning to Tucson from Chicago and landed about 10:00 pm local time. The approach was very bumpy and winds were still gusty from the east to southeast. The air was heavily laden with dust, giving the 3/4 moon a very strange and dirty yellow-brown appearance.
Thursday, June 12, 2008
Appears that there may be high-based, dry lightning storms over the mountains of far southeast AZ this weekend. Definitely not good, given the extreme dry conditions of last two and a half months. Only 0.09" of rain here at house since March 17th!
In the longer term, the GFS ensemble members keep a strong, middle-level anticyclone north Mexico/southern Plains, and then tend to shift it northward during last 10 days of month. Throw a tropical disturbance into this pattern and who knows what we might see down here.
I'm off to Wisconsin where it will be green and wet and probably muddy.
Friday, June 06, 2008
0000 UTC soundings with superadiabatic layers aloft apparently due to wetbulbing:
UIL SLE BOI OTX FWD OAX SHV MSP TLH BMX APX MFL
ABR has an extreme super layer aloft but it is not due to wetbulbing. LBF flight missing.
12000 UTC soundings with superadiabatic layers aloft apparently due to wetbulbing:
UIL SLE ILX OTX DVN SGF
OUN sounding appears very strange for unknown reasons.
Friday, May 23, 2008
Overview of suspect data for 0000 UTC 23 May 2008:
Superadiabatic layer(s) aloft:
LBF UNR SLE TWC FWD LIX TLH LCH MFL BUF
Additionally - the LBF flight was incomplete; the MHX flight was missing all winds except that at the surface; the LIX flight also exhibited a warm spike and extremely noisey data; the JAN flight was terminated.
Overview of suspect data for 1200 UTC 23 May 2008:
Superadiabatic layer(s) aloft:
LBF UNR TWC FWD OUN TLH MHX DVN BMX BNA APX RNK
Additionally - the UNR and MFL flights exhibited extreme noise in the RH data and the bizarre TLH flight was terminated.
Thursday, May 22, 2008
Visually obvious problems appear in the sounding data as per:
Warm spikes at GGW RIW
Superadiabatic layers aloft at GJT GGW(3) SHV TOP OMA AMA JAN TLH MFL(2)
Suspect layer (Opposite of wet bulb superadiabatic) at UIL SLE MFR APX
Some of these are quite amazing. The sounding data can be easily viewed at Univ. of WY's upper air page:
Note that two of the suspect soundings are from non RRS stations - TOP which flew into an MCS and MFR which showed a weak Op-Super layer from its VIZ instrument.
I call the strange layers "Op-Super" that occur when sonde exits cloud into drier and warmer air and T increases rapidly but RH stays at 100% for a while. This likely indicates a hygrister problem vs wet bulbing under same conditions which indicates a wetted thermister.
Friday, May 16, 2008
I have had time to take a quick pass through the morning soundings.
Soundings having a super-adiabatic layer aloft include:
MAF BRO LIX TLH MHX GYX
Soundings having a warm spike aloft between 0 and -10C include:
GJT LIX IAD
Too busy today to take a careful look at any of these.
Thursday, May 15, 2008
AMA FWD BNA LBF LZK JAN LCH
The problem at LBF was due to an intense warm spike.
The too cool layers in several of these soundings cause computed CAPE to be inaccurate.
I cross-checked the NCAR RAP plots with those at Wyoming this morning, and all the above
problem soundings were similar at each web page.
LCH is the most bizarre sounding of the bunch. The instrument apparently was launched into
a thunderstorm or deep convection.
Data were missing for for a short period.
Operator interpolated data for the missing period.
A saturated point was interpolated with T/Td spread shown as //
The NCAR Rap sounding decoder did not interpret the // correctly,
producing the very strange sounding on their web page.
The decoders at Wyoming and SPC plotted the data correctly.
Wednesday, May 14, 2008
Figure 1 - KFGZ
This sounding indicates a very dry layer of almost 100 mb vertical extent just above 700 mb. It had been raining for several hours and at the time of release Flagstaff was reporting moderate to heavy snowfall. The snow continued for several hours after sounding time. The dry layer certainly does not seem physically realistic, given the steady precipitation event that was underway.
Figure 2 - KFWD
This morning's sounding at FWD indicates a strongly super-adiabatic lapse at about 710 mb. This excursion causes a layer that appears to be several degrees too cool from about 710 to 550 mb. The net result is that sounding analysis software routines would produce CAPE values that were likely too great. Since the sonde did not, apparently, rise into a very dry layer, the reason for the super-adiabatic layer aloft is not clear.
Both of these soundings may illustrate random instabilities within these two RSS sonde's internal electronics, but this is just a guess on my part.
Thursday, May 08, 2008
My quick look at the soundings last evening identified two RSS flights that exhibited strongly super-adiabatic lapse rates in shallow layers aloft. These soundings were taken at Birmingham, AL, and Sterling, VA.
Note that the RRS operational procedures indicate that layers such as these should be removed via manual editing by the operator, and provide instructions for how this should be done.
Figure 1 (00Z BMX)
The layer of interest here extends from about 630 mb to 610 mb. The sonde apparently had moisture on the thermistor, and perhaps on the hygristor. When the instrument exited a deep, cloudy layer it encountered very dry air aloft and evaporative cooling of the sensors probably produced the super-adiabatic layer.Figure 2 (00Z IAD)
The layer of interest here is only about 10 mb deep and is located near 740 mb. The reason for this super-adiabatic layer is not obvious, since the entir atmosphere appears to be quite moist. The sounding apparently did not exit cloud into a very dry layer above. It is possible that the instrument was in a saturated updraft and exited the updraft suddenly. It is also possible that the hygristor did not respond adequately to a layer that was considerably drier than the data indicate.
During the next few months I'll be paying particular interest in identifying soundings in which bad data have complicated the diagnosis of CAPE or potentially caused forecasting difficulties.
If readers note soundings that seem to be candidates, as per above, for closer examination, please feel free to alert me to them. Thanks, Bob email@example.com
Wednesday, May 07, 2008
Today's winning example of a strange sounding is that taken at Ft. Worth TX at 1200 UTC.
Monday, March 17, 2008
The system produced more precipitation than I was expecting, given the very low precipitable water values. Here at the house, I measured 0.29" through 7 am this morning and light showers remain in the area. Low this morning was 33F.
Precipitation yesterday was from convective showers in the cold, unstable air. I did not hear any thunder here at the house. During midafternoon northern and western parts of the Tucson metro area had heavy showers of graupel (AKA snow pellets) and the ground was covered in some spots.
Perhaps some more of this today, before the system moves on east. It's hard to know how unstable it is this morning, since the somewhat critical Tucson upper-air sounding was missing both last evening and again this morning.
The NWS forecast this morning (see below) mentions the possibility of showers, thunder, and sleet. While showers accompanied by graupel may occur, the liklihood of sleet is extremely small, today or with any winter weather event in the Tucson metro area, since sleet results when raindrops fall through a layer of subfreezing air at or very near the surface. Definitions of graupel and sleet are also below.
Today: A chance of rain showers possibly mixed with sleet, mainly after 11am. Some thunder is also possible. Partly sunny, with a high near 53. South southeast wind 9 to 14 mph becoming west northwest. Chance of precipitation is 30%. Little or no snow accumulation expected.
From the Glossary of Meteorology:
snow pellets (Also called soft hail, graupel, tapioca snow.) Precipitation consisting of white, opaque, approximately round (sometimes conical) ice particles having a snowlike structure, and about 2-5 mm in diameter. Snow pellets are crisp and easily crushed, differing in this respect from snow grains. They rebound when they fall on a hard surface and often break up. In most cases, snow pellets fall in shower form...
sleet or grains of ice, generally transparent, globular, solid grains of ice that have formed from the freezing of raindrops or the refreezing of largely melted snowflakes when falling through a below-freezing layer of air near the earth's surface....
Wednesday, March 12, 2008
The ECMWF and the GFS ensemble members are all pretty much in agreement now, indicating a strong wave digging down the west coast, with the eventual cutoff affecting us from about 96 to 144 hours - from 00 UTC model runs last evening.
There are about 5 waves strung out across the northern Pacific and it's not clear which one kicks up the ridge into AK, forcing the wave down the coast. Obviously all the models have keyed on one of these to be the agent of change.
The models appear to predict about a quarter to half an inch of precip at lower elevations by late Monday afternoon. Uncertainties this far out - how long will the wave affect SE AZ - some model runs keep it more isolated from the main flow to the north; how much moisture will the system pickup (the ECMWF hints at better moisture flowing northward toward the end of the event, while - surprise - the GFS members stay drier). Only 10 of 12 GFS ensemble members predict measurable rainfall at lower elevations in SE AZ during the event.
Current fcst POPs for both TUS metro and also top of Catalinas max out at 30% for Sunday night. PHX has issued a hazardous weather outlook for this event already (see the nice early am FD from PHX). Will be interesting to watch how this event evolves.
Different topic - My total precip for Dec/Jan/Feb here at house was 5.84 inches -not bad for a la nina winter! Actually not bad for any of past ten winters - beaten only (I think) by the 97-98 el nino winter.
Thursday, January 31, 2008
There was measurable rainfall on only 4 days but the total, mostly from the storms of the 7th and of the 27th/28th, was 1.00 inch. The storm late in the month produced much flooding and runoff after very heavy rains at higher elevations. The Rillito wash is still running today.
After a very cold December (our gas bill for heating in December was the highest ever during our ten years in the house), January was also fairly cold. There were 18 mornings with low temperatures of 32F or colder. Half of these days had lows of 27F or colder.
The coldest mornings occurred on the 18th - 20th with readings of 20F, 20F, and 21F. This morning, the 31st, was also cold with a low of 22F. There was a period of 14 consecutive days from the 10th through the 23rd with lows of 32F or colder.
So, probably another big gas bill.
Appears that February will also start out unsettled with perhaps more rain during this strange la nina winter.
Tuesday, January 22, 2008
This morning's NAM indicates a precip period Wednesday night through Friday morning. Interestingly, the operational GFS (from 00Z last evening) shows little at Tucson during this period. The GFS tends to keep the subtropical moisture to the south as the first middle level low swings around and minors out, while the second system digs in. The role, if any, of the system out around 140W and 30N is not clear in the model forecasts.
The GFS and the ECMWF (both from 00Z last evening) indicate that the second wave will pull the subtropical moisture much further north and provide the most significant event out toward the weekend. The precip forecast of these long range models is fairly different. The GFS indicates the main precip near Tucson to occur Saturday night and to amount to around a quarter to half an inch. Whereas, the ECMWF indicates that the main precip event would also be Saturday night, but rainfall amounts near Tucson of a half to a bit more than an inch are predicted by this model.
So, the summary is that there may be two distinct precip events over southeastern Arizona with the weekend event likely being the more significant one. Will be interesting to watch how this very complex situation actually evolves. Regardless we're definitely having a more interesting la nina winter than one might have expected!