Very Active Period Continues

After a rainy, cool and heavily clouded weekend, the new week begins with the western US S/W at 500 mb phasing and merging with a Pacific vorticity max over southeastern Arizona during next 24-hours. So a showery day on tap. Then by Thursday another broad and diffuse S/W moves across the west coast. This feature consolidates, strengthens and moves southeastward. This S/W's vorticity max passes very close to Tucson by Thursday evening and the evolution of this feature should be watched closely - currently the NAM forecasts its main precipitation impact to be in Arizona's mountains and New Mexico.

By next weekend a much stronger wave at 500 mb comes ashore and cuts off over the Southwest (according to the GFS forecast runs from last evening - 00 UTC 22 Feb 2010).

The GFS ensemble mean and spaghetti plot for the Northern Hemisphere valid next Sunday Feb 28th at 5 am are shown above. It is quite interesting that the ensemble spread of forecasts and uncertainty is greatest over the Western US; however, all 12 members forecast precipitation over southeastern Arizona for the 12-hours ending at 156-hours. It is also interesting that the operational GFS (white contours on right panel) is an outlier relative to the other members, moving the trough/cutoff eastward faster than the other forecasts.

Regardless, more rain on track for Tucson - noticed driving around over the weekend that our winter weeds have begun a period of wild, rapid growth. The same is true for the thousands of potholes lurking out there on Tucson's streets!

Some Quick Updates

Sunday afternoon - February 21, 2010 Photo above shows a light shower on the Catalinas



Yesterday evening another band of rain showers moved into the Tucson greater metro area, adding to the midday rainfall amounts. Here at the house the final total came to 0.38". Amounts for the 24-hours ending at 7 am across eastern Pima County ranged from about 0.20" to around 0.75" with the higher amounts in the foothills below the snow level and in the Redington Pass area.


Another system is approaching from the north this afternoon. The GFS ensemble members have all been forecasting precipitation over southeast Arizona with this system since at least 96 hours ago (for the 12 hour period ending at 5 am on Tuesday morning).


Interestingly, there is yet another forecast on the weather page of the Star this morning that is out of sync with the forecast that NWS has had out (60 to 80% for tomorrow) for a number of forecast cycles. I assume that someone isn't checking either the NWS forecast nor the GFS ensembles nor..... regardless, weather followers this morning would find 50% chance of rain tomorrow in the newspaper and 80% chance in the current NWS forecast. Hopefully these problems are in the way AccuWeather does it forecasting from back in Pennsylvania!


The GFS ensemble members are predicting (almost unanimously) another precipitation event over southeast Arizona next weekend on Saturday night and Sunday (February 27 and 28). Will be interesting to watch to see if subsequent model runs remain consistent with this morning's predictions.

Fast-hitting Cold Rains

Rain event, so far, was characterized by a fast-hitting area of cold rain that swept across the Tucson area from about noon to 2:30 pm. Every ALERT gauge in the Pima County network had measurable rain last six hours, except for the high elevation stations, which had a burst of heavy snow. Thus a 100% coverage event that brought amounts of 2/10 to 5/10 of an inch - 0.24" here in the backyard. Snow level came down fairly low, so that some heavy cover is peaking out from the Catalinas at about 3500 to 4000 ft MSL. Photos above both from a bit before 1 pm show the rains and clouds obscuring the Catalinas and that it was snowing up on Kitt Peak. And the next act will be?

Clouds on the Increase

Clouds are increasing rapidly from the west and southwest ahead of the Pacific S/W. Rest of the day should be quite interesting here in Tucson area, as well as much of Arizona. Bottom image above is the nearly current visible satellite imagery showing the distinct line of cloudiness that is advancing across the state - note apparent mesoscal circulation near Blythe, CA. Top photo above shows that Kitt Peak is already in the clouds!

Beautiful Spell of Weather Ending

After a week or so of beautiful, dry sunny weather here in the Southwest, the large-scale pattern is changing and a week or more of unsettled, winter-like weather lies ahead.

There is currently a S/W or cutoff west of southern California. This feature breaks under the large, west-coast ridge at 500 mb and moves quickly eastward across the Borderlands under the larger S/W that is over Idaho this morning. The NAM forecasts widespread precipitation ahead of both S/Ws - see 48-h precipitation forecast at top that ends at 5 pm MST Sunday afternoon.

The Idaho S/W at 500 mb digs to the south-southwest behind the first wave and is moving across Arizona on Monday afternoon and night, bringing continued chances of precipitation. The second figure above is the GFS 96 hour forecast - the GFS ensemble members (from 00Z last evening) all forecast precipitation over southeastern Arizona for the 24-hours ending at 5 am next Tuesday. So, the models indicate an unsettled period with the ensembles indicating 100% POPs but light precipitation amounts over low elevations - this stormy period may continue through the coming week. So, more weather to watch.

Storm Moves East

Web Cam view from Computer Sciences yesterday afternoon shows another damp, dreary afternoon on the U of A campus. This event brought 100% coverage of precipitation over all of eastern Pima County, and the RAWS observations seem to indicate that all of southeast Arizona received measurable precipitation. Rainfall amounts at lower elevations around Tucson were mostly in the 2/10 to 5/10s of an inch range. For the first time in weeks both TUS and DMN surface observations indicated thunderstorms were occurring in the metro area - didn't hear any thunder here at house nor observe lightning. Rainfall here in backyard was 0.34". This makes the rainfall total at house for 2010 an amazing 4.37 inches. Skies at sunrise are covered by very low cloud cover and there are possibly a few sprinkles still around. The upper-low has moved off to the southeast of Arizona. The forecast models indicate a building ridge over the west at 500 mb that will persist for around a week, allowing things to dry out a bit.

Another Cutoff Digging down the Coast

The 13Z water vapor image above has a nice view of the current cutoff just west of San Francisco. This feature is heading south and will eventually move ashore in the far Southwest US near San Diego. The image also shows a very large area of subtropical moisture west of Mexico. This morning's NAM run (Tues 9 February) takes the bulk of this moisture blob across Mexico and into New Mexico and west Texas. But the model forecasts do manage to pull some of this up into southeast Arizona before the event ends. So, an interesting interplay of features to keep and eye on!

Nice Rain Event

The photo below and this one show shots of the Catalinas and of Kitt Peak early this afternoon as a widespread rain event is winding down in the Tucson area. Some convection is possible as the sun is coming out and trying to heat things up a bit, but the general area of showers and rain has moved south and east. This has been a much better event than that of last Tuesday night and Wednesday morning. Here at the house at 7 am we had gotten 0.37" of rain in the pre-dawn hours, and between then and noon we received another 0.60" of rain. Thus, at this time there has been 0.97" of rain here. At 7 am 41 of the 97 (40%) Pima County ALERT gauges had recorded measurable rainfall and then between 7 am and noon 100% of the gauges recorded rain or snow. So, a nice, widespread precipitation event. At this time the models are forecasting a somewhat similar event to occur across the Borderlands next Wednesday night and Thursday morning. So, the progression of weather systems from the Pacific into the Southwest continues, at least for a few more days, giving us a very interesting el nino winter!

Another Rotten Forecast in Sunday Star!

For the second Sunday in a row, the Arizona Daily Star weather page has given readers a really bad forecast! We have just had a very nice rain event across Tucson and all of eastern Pima County. I slogged out through moderate rain this mroning to bring in the paper and found that we had a "30% chance of isolated showers and rain today." The NWS had forecast 60% for last night and 70% for today yesterday afternoon - not perfect, but certainly much better than what the paper had. I suspect that the entire weather page and forecast is being supplied by AccuWeather (which obviously had much more important weather events to focus on yesterday!). If this assumption is correct, the big mystery is why KVOA Channel 4 wants their logo and meteorologists' smiling faces bannered alongside AccuWeather's rotten forecasts?

Event Postmortem

The latest weather event has moved eastward and turned into quite a rain-maker for the lower Mississippi Valley. See the early morning radar composite above, from the CoD weather page. I got several e-mails about the event here in southeastern Arizona, so here's a summary.


First, the NWS forecast for Tuesday night (Feb 9/10) was for 100% POPs. When I took a look at
things on Tuesday evening - around 6:30 pm - the NWS forecast looked to be right on track. The IR satellite image showed a huge area of cold cloud that seemed to be moving northward right up toward Tucson. The models were in agreement, forecasting rainfall everywhere in the southeast part of state with some nice amounts indicated by the model QPF. But the model(s) obviously didn't get the movement of the disturbance quite right and were just enough off on the eastward component to change us, locally, from a forecasted good event to an observed almost zip.


I put the radar precip up on the blog yesterday morning to illustrate what a bust the model forecasts were here, right around Tucson. So it goes! I saw some amounts off to Tucson's southeast over an inch yesterday morning - so it just illustrates how a very small model error can really impact us. The event that's just ended provides a huge contrast to the major event in late December that was forecast very consistently for days and illustrates that sometimes the nodels can lock accurately onto hemispheric forcing and be extremely reliable but at other times be fickle even at 12-hours.

As for precipitation yesterday as the system headed east - here at house we got 0.10" and about 65% of the Pima County ALERT gauges had measurable rainfall in last 24 hours. Amounts were mostly around a tenth of an inch or less, with a few spots receving about a quarter of an inch. Arivaca had 0.63", Nogales had 0.44" and Douglas had 0.61" and some RAWS data indicated over an inch amounts in the far southeast part of the state. The more significant part of the event stayed to the south and east of the Tucson Metro NWS forecast zone. And so we have to hope that the next two events coming in off the Pacific do better in getting rain on the ground.

Rain Shifts Mostly To East

The first 12-hours of the significant rain event that the models have been predicting for the Tucson area pretty much fizzled out. The morning storm totals from radar (7 am 3 Feb 2010) shown above indicate little in the way of rain accumulations except down around Sierra Visita. The most significant rains with the subtropical disturbance have stayed in Mexico and also shifted eastward into southern New Mexico and southwest Texas. Here at the house we had some sprinkles after dark last evening but only had a trace in gauge this morning. Only 14 of 97 (about 14%) Pima County ALERT gauges had measurable rain during past 24-hours and amounts were quite light, except for a couple of sites in the Catalina Mountains - Mt. Lemmon 0.39" and White Tail 0.31". This morning's NAM run forecasts some westward shift in the showers during the day today but keeps Tucson right along the northern gradient of the heavier rainfall. The morning TWC sounding indicates only a tiny sliver of mid-level CAPE, so forcing will be mostly orographic and large-scale vertical motion for any rains we do get. We'll have to watch today to see if this much-advertised, model-predicted high POP event actually brings us enough rainfall to wet down the streets.

January 2010 Comes to an End

January 31, 2010 draws to an end with a scenic sunset. Photo above taken at 5:55 pm MST, looking north at the Catalina Mountains from our backyard.

Random Weather Grumbles

Have some grumbles about weather products I've examined today.


1 - Arizona Daily Star and KVOA weather page in this morning's Sunday paper. The chance of rain is given in the paper as 0% for both Tuesday and Wednesday. Shown above is the NAM forecast of 48-hour rainfall amounts for the 48-hours ending at 5 pm Wednesday afternoon. Hmmm, somebody is not coordinated here. There is a statement on the Star weather page that: Forecasts and graphics, with the exception of KVOA[sic], provided by AccuWeather.com. I don't know what exactly that statement means. It could be that everything on the Sunday Star weather page is from AccuWeather, except for the photo of Matt Brode and the Channel 4 logo. What I do know for sure is that the forecast for rain during midweek did not suddenly pop into the NWS forecasts this morning after the newspaper had gone to press last night!


2 - From the 1:45 am Sunday morning (31 Jan 2010) Tucson NWS Forecast discussion: SOME ENERGY ROTATING AROUND THE SRN PERIPHERY OF THE MAIN LOW OFF
THE COAST OF THE PACIFIC NW WILL SWING THROUGH NRN BAJA. Hmmm, I don't know what exactly this statement means and "energy" is not defined in the NWS glossary for the general reader. The use of this kind of loose terminology in technical discussions is one of my pet peeves. Perhaps the writer was referring to some kinetic energy? But I think not - I suspect that this is jargon for - a local maxima of cyclonic vorticity at 500 mb. Or perhaps??


3 - From the 2:35 pm Sunday afternoon (31 Jan 2010) Tucson NWS Forecast discussion: SHORT WAVE RIDGING WILL BE TRANSITIONING ACROSS THE STATE IN ADVANCE OF NEXT PACIFIC STORM. Again, it's not very clear what this statement means precisely. Meteorologically, "ridging" usually means the building or strengthening of a ridge at some level in the atmosphere. Transitioning is used here, I am fairly certain, to mean - moving over or translating across the state.

Again, just a couple of my pet peeves about imprecise technical writing.

The upside is that it again appears that we'll have some weather to watch during the coming week!

Latest Storm Creates Havoc to East

The storm over Arizona has moved on eastward, encountering very cold air over southern Plains and mid-Mississippi Valley, and producing widespread ice and heavy snow. Photo above is yesterday from Amarillo, Texas, where I-40 was closed both to west and east.

Here at house another 0.13" of rain fell during the morning yesterday (Thursday the 28th), bringing the month's total to 2.96" - which is the most January rain during the 11 years I've had my rain gauge up. Previous wettest January was during 2001 when I measured 2.31".

New Snow on Kitt Peak

Webcam above shows that it was snowing on Kitt Peak at midmorning. Elevation of Kitt Peak is about 6800 ft MSL. Top photo shows a soggy U of A campus at late morning, with the Catalinas completely obscured.

Weak 500 mb Low Spinning Overhead

Weak 500 mb low is spinning almost directly overhead this morning. It has brought widespread rains overnight with amounts in southeast Arizona generally from a tenth to about an inch. The rain continues off and on this morning with additional accumulations.

GFS Spagetti Chart At 336 Hours

The GFS spagetti chart for 336 hours from the model ensemble indicating that most members continue to indictate a Pacific split in the flow with two principal storm tracks over the continent.

The two 500 mb height contours shown are 522 and 564 decameters. Comments most welcome!

More on Pacific Storm Track

Shown above is the GFS 200 mb operational forecast for 336-hours valid 00 UTC Sunday February 7, 2010. The very strong west-to-east jetstream continues across the Pacific into February according to this model's forecast. These are very interesting forecasts and we'll have to watch how they verify during the coming two weeks of predicted active weather.

Active West-To-East Pacific Storm Track Forecast to Continue

Shown above is the ECMWF four-panel forecast for 168-hours from 00 UTC Sunday January 24, 2010. It indicates a continuing, active progression of S/Ws from off the Pacific and into the continental U.S. The main change indicated by this forecast is that the storms are no longer blocked over the West and progress all the way across the country.

The Tucson NWS office has prepared a summary of weather observations from the past week and posted it on their web site - see:

http://www.wrh.noaa.gov/total_forecast/getprod.php?wfo=twc&sid=TWC&pil=PNS

The Flagstaff NWS Office has both a narrative summary of the past week's weather in northern Arizona and a listing of snow and rain totals at:

http://www.wrh.noaa.gov/total_forecast/getprod.php?wfo=fgz&sid=FGZ&pil=PNS

Big Storm(s) of January 2010 Wind Down

Photo shows more snow and even icicles at Kitt Peak this morning. Rain began after dark here at house last evening and continued past midnight. There were three distinct rain events here

and all were during the night - between sunset and sunrise except for less than a 1/10" which fell yesterday between 7 and 8 am. First event (one could call each of these separate storms embedded within the larger Pacific trough) was on Tuesday night and produced 0.54" of rain here; second events was on Thursday night with 1.18"; and third event was Friday night (last night) with 0.69" in the gauge this morning [four-day total of 2.41"]. Other parts of the state had more spectacular totals and the Salt/Verde drainages have record 5 day totals for rain/snow. Lots of snow; road closures; and wind with the first two events. Here in the southeast part of state there was little lightning and thunder during the four days - none here at house and none at the regular observing sites. This event will certainly help with water supply and dampen the terrible drought we've been experiencing. May be some convective showers today, but we're basically back to watching the evolution of features over the Pacific for the coming week.