20220726

 Previous Forecast

It was another busy day for much of the state.  The main characteristic of the activity was, not unsurprisingly, heavy rain.  Areas west of Phoenix, NW Arizona, and north of the White Mountains were especially active.

WRF forecasts struggled in this hard-to-forecast regime.  The WRFGFS did the best as it did have some idea about the Phoenix late-night activity, but it was on the wrong side of the city.  

Discussion

I counted 3 MCVs/ITs near or in the state this morning.  One near Vegas, another in far NE Arizona, and another over the Phoenix area.  The Phoenix circulation has remained mostly stationary for the past 24 hours as the synoptic-scale circulation at mid-levels is so weak.  The CONUS synoptic pattern remains the same, with an amplified ridge in the west and a broad trough over much of the northcentral and northeastern CONUS.

The upper-level IT has stalled out over the Big Bend region and continues to put Arizona under weak divergence/difluence, which continues to be generally favorable for supporting storms.

PW continues to be extremely high around Phoenix and southwestern Arizona, around 50-54mm.  SE Arizona is also high with 40-45mm.  The Tucson sounding continues to be nearly saturated, and there is a bit more MLCAPE than in previous days.  The wind profile is bad as most of the troposphere is light and variable. Thus storms aren't going to move off of high terrain much.

The Phoenix sounding had some problems above 500mb, but enough is there to say it looks worked over with the "green onion" profile.  CAPE is relatively low, but as we've seen, with the MCV hanging around and this amount of moisture, low topped storms can go just about any time.

Initializations

There are issues with the WRFRR crashing, so the 9 and 12Z ran short.  Most initializations did a reasonable job with the complex situation.  The exception was the 12Z RR, as clouds were too thick and covered too much of central Arizona.   It also initialized a big severe storm near Phonenix, so it's a good thing it crashed.  There is also a large MCV in Sonora, which was not well initialized by any.

Day 1

The 850mb cyclonic circulation off of BCS is still there but is starting to move towards the west.  Drier 850m air begins to advect into southwestern Arizona by the afternoon.  Elsewhere, it remains very moist.

CAPE is generally low but with some areas of moderate to high values.  It's not realistic to say if these are accurate, as there are so many clouds around that most GOES CAPE is missing.

Storms get off to an early start and are over the higher terrain of southeastern Arizona and the Flagstaff area by noon.  

It looks like a few storms manage to develop in the Tucson area by mid-afternoon.

It does look favorable for Tucson as CAPE is good, at 1000 J/kg, and there is no evident cap or inversion.  A nearby outflow boundary will probably be enough to set off a storm or two, and with 43mm of PW and storms not moving much due to a lack of steering, precipitation amounts will be high.

All the WRFRR runs are missing, so only the WRFGFS and HRRR are plotted.  They generally keep most of the heavy rain over the higher terrain surrounding the city.  Typical.

Most storms end by early evening, but Phoenix might see a few pop up, much like last night.  A few runs also have some early morning activity for areas near Phoenix.  

The potential is certainly there with CAPE above 1000 J/kg.  Heavy rain and flash flooding are likely as PW is 50mm!

Day 2

Again, it's a very challenging forecast environment, so it wouldn't be prudent to say much beyond plenty of moisture remains over the state.

CAPE is forecast to be moderate to high over much of southeastern Arizona and up towards the Rim and the White Mountains.

48-hour accumulated precipitation is expected to be very heavy for some locations, as high as 3-5". NW Arizona is also at increased risk for heavy rainfall.