20210716

 Previous Forecast

Heavy precipitation fell yesterday morning west of Tucson, which resulted in a cool and stable air mass for the rest of the day with little or no activity.  Scattered heavy rain fell over southeastern Arizona, and storms moved off of the high terrain towards Phoenix, with one or two making it into the valley.  I'm a little surprised that activity wasn't more widespread for Phoenix as the 0Z sounding indicated 1400 J/kg of MLCAPE and a PW of 2.02".

It was a mixed bag regarding WRF accuracy, which was expected due to the complex nature of the initializations.  The WRFGFS (6 and 12Z)  did move storms into the Phoenix area, but elsewhere, it had too much activity as it could not initialize the southern Arizona activity.  

Discussion

Once again, showers and a few thunderstorms have developed over parts of southern Arizona.  This is due to an inverted trough over far SW NM and a very moist and unstable air mass over southern Arizona.  The Tucson 12Z sounding had almost 2K of MLCAPE and 1.93" PW!  No model run was able to predict this amount of CAPE, and I'm shocked that there aren't more storms about.

Art Douglas sent me the SMN/Conagua precipitation map for the first 1/2 of July, and much of Mexico is also having a good Monsoon.

Much of NW Mexico is average or above average.

Initializations

Widespread clouds and embedded storms are present over much of south-central and southeastern Arizona.  GOES PW indicates 40mm or higher over much of southwestern Arizona and more than 25mm all the way up to Vegas and into NM.  PW is also high along the Mogollon Rim.

The 6Z WRFNAM was no good as it initialized strong storms over much of southeastern Arizona and continued them into the morning hours.  While it had the right idea, it was too far east and too strong.  The 6Z WRFGFS isn't too bad as it has clouds and a few showers in the correct location, but not enough activity.  The 9Z WRFRR looks pretty good as it has clouds and showers/storms mostly in the correct location.   The 12Z RR initialized too widespread showers and storms, and the 12Z NAM had too few.  The various RR initializations also have the IT too far to the north in NM.   There are no good initializations, but the least bad appears to be the 9Z RR.  Confidence, at least for southern Arizona, is low.

Day 1

Moisture continues to steam into the state as the never-ending Gulf Surge continues.  PW has been near or setting all-time records for the date for the last week.  Today, the old record was 1.74".

CAPE is limited for areas that had morning clouds and precipitation.  

Thick clouds remain over much of far southern Arizona into the early afternoon, keeping heating to a minimum.  It looks like the areas of interest are north of Phoenix and maybe, if clouds clear out, far southeastern Arizona.  

Later in the afternoon, strong storms are widespread around the Flagstaff area and in eastern Arizona.  

Steering flow continues to be favorable for moving storms into the lower elevations.  Phoenix has only a moderate amount of CAPE, at best, so as the storms move into the valley, they weaken.  Still, they could produce very heavy rain.

The only run that seems to have a handle on what is going on is the 6z WRFRR.  It again predicts heavy rain for areas around Flagstaff and along the Rim into the White Mountains.

Day 2

Will there again be morning storms around southern Arizona?  Perhaps, as some model runs have ~500 J/kg of CAPE plus the influence of the westward-moving IT.

Forecast confidence will be low again due to the complexity and uncertainty of the previous 24 hours.  PW may decrease a little over eastern Arizona, but it continues to be at record highs over central and western Arizona.

The CAPE forecasts are all over the place, with some runs with almost none and some with a fair amount over southern Arizona.  I have no idea what it's going to look like tomorrow.

The IT opens up and is located somewhere over far NW Sonora, resulting in mainly southeasterly steering flow.

There might be some activity in southeastern Arizona later tomorrow afternoon or evening.  Confidence is low!