Sunday, February 28, 2010
Nice visible satellite image of the clouds over southeastern Arizona this morning.
Yesterday morning Chuck Doswell commented:
Yes, the models have made quite a bit of progress from the days of the barotropic model. We're both old to recall those days! I suspect we can reasonably expect continued model forecast improvements, including predictions of uncertainty, although the limits to useful predictability may never move much beyond where they now are. The limits imposed by nonlinearity are pretty solid.
Saturday, February 27, 2010
Friday, February 26, 2010
The much advertised precipitation event for this weekend has been pushed back in time a bit by this morning's NAM forecast run. The very complex and persistent 500 mb cutoff in the east (see top graphic) has several vorticity maxima rotating around its western and southern peripheries. These are holding the system in place longer and preventing the rapid movement eastward of the strong S/W and cutoff forecast to be over the Southwest Saturday night and Sunday morning. The NAM is now forecasting a more substantial precipitation event for southern Arizona - see bottom graphic with 24-hour forecasted precipitation for period ending at 5 pm Sunday afternoon - with the bulk of the predicted precipitation occurring during the day Sunday.
Tuesday, February 23, 2010
Monday, February 22, 2010
Sunday, February 21, 2010
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.
Saturday, February 20, 2010
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 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!
Friday, February 19, 2010
Thursday, February 11, 2010
Tuesday, February 09, 2010
Sunday, February 07, 2010
Thursday, February 04, 2010
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.
Wednesday, February 03, 2010
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.