20190807

Previous Forecast
It was a dull day, with most areas suppressed.  Some activity developed in southern Arizona, but the big storms were just south of the border in Sonora. 

The lightning data corresponds quite well to the MRMS satellite(IR?) derived precipitation estimates.

 The WRFGFS was the worst while the rest were quite good, at least in Arizona.

The WRFNAM and WRFGFS missed most of the Sonoran deep convection which can result in inaccurate day 2 forecasts for Arizona.  The WRFRR forecasts were a bit better with the 15Z being reasonably accurate.

Initializations
In spite of all the activity in Sonora, I couldn't find a remnant MCV.  In fact, all the debris clouds have cleared quickly, and it's mainly clear at 16Z over Arizona.  The 500mb plot indicates that the ridge axis stretches from Washington down to west Texas with a deep trough along the coast.  This results in mainly southwesterly winds over Arizona which is a negative, but at least there is somewhat cooler air in the vicinity: -9C at San Diego and -7C at Empalme.

The only real feature of note is the departing trough over northeastern Arizona which was initialized well.  Clouds were initialized well, and all the model runs burned them off during the morning hours.  Both the 12 and 15Z RR had minimal PW errors while the GFS and NAM had moderate to large errors in Arizona and Sonora.  Again, the WRFRR is the favored run and should perform well assuming it's over its recent problem of not enough deep convection. 

Day 1
The Tucson 12Z sounding indicates that MLCAPE is considerable at around 1300 J/kg and the airmass is very moist with a PW of 43mm.  Also, the residual boundary layer is well mixed to 500mb with only minimal lower cooling.  Just based on this, it looks like there is the potential for a big day.  The negatives are light and variable winds below 500mb and strong upper winds which will again strongly shear anvil tops off.

500mb temperature forecasts for eastern Arizona continue to have unfavorable warm air at around -5C.  Western Arizona is a bit better with -7C so some storms may develop out that way today. I just looked at the radar after I wrote the previous sentence and there is already activity not far from Yuma.  The 14Z sounding from Yuma indicated 800 J/kg MLCAPE and surface-based of 1200.  That is quite a closed low west of San Diego.  Maybe it will eventually eject over far western Arizona?

After thinking it was going to be a fairly active day, I am confronted with this:

There is almost no activity forecast by the 12Z runs for the southern 1/2 of the state today, which is a big surprise.    My only explanation is dry air advection from the southwest around 700mb and entrainment into the top of the CBL is responsible.

Afternoon CAPE is more than sufficient to support storms.  Is this another case where the WRF configuration fails to sufficiently predict a situation like this?

The 15Z WRFRR is now available, and it tells the same story as the previous runs; little or no deep convection this afternoon.

Look at Phoenix this afternoon, 1600 to over 2000 J/kg of CAPE!  My only guess is that there is subsidence due to the departing trough plus dry air entrainment at the top of the CBL which results in limited activity.  There are good reasons for the lack of activity, but I'm still concerned WRF may be underpredicting storms.

The WRFRR develops some strong storms over far southeastern Arizona this evening.

The WRFGFS and WRFNAM develop very strong storms over western Arizona this evening.  I question why the WRFRR does not as the situation looks favorable.

Day 2
It continues to be quite moist over much of the state.  Hopefully, storms will be more plentiful.

CAPE is more than enough.

Southwesterly flow dominates the state, and some slightly cooler air moves into western Arizona.  Eastern stays very warm at around -6 to -5C which will again be unfavorable for deep convection.

I'm afraid it's more of the same with dry air entrainment at the top of the convective boundary layer.

Here's the bad news.  Only scattered storms over the higher terrain.