20190725

Previous Forecast
The 15Z WRFRR and 12Z WRFGFS were quite good as they forecast the activity in NW Arizona and in Pima County quite well.   The only issue was the model runs had the storms a bit later in the evening whereas a severe thunderstorm hit Marana around 6pm.  This was the view from mid-town around that time.  No action in Tucson but we did have a magnificent sunset.

Initializations
NAM data from NCEP was corrupted, so no WRFNAM today.  The state is mostly clear, and satellite imagery didn't reveal anything interesting.   The 500mb chart looks about the same as it has the past few days with the anticyclone centered near the Four Corners.

IPW initialization is excellent and today is one of the more accurate initializations so far this season, mainly because it's so simple!

Day 1
Yesterday's runs indicated that today would have limited activity, but looking at the 12Z Tucson sounding, there may be a bit more than was expected.   It's very moist in the lower troposphere as the surface Td is 64F and PW is around 38mm.  This results in a mixed layer CAPE of almost 1400 J/kg.  Steering winds are quite weak but maybe enough to nudge some storms into the lower deserts.  Even Phoenix has around 700 J/kg of MLCAPE.

A surge is underway this morning and is forecast to continue today keeping PW high over much of the state.  The drier easterlies in NM have weakened, and the surge is pushing moisture eastward.

CAPE is high to very high over parts of southeastern and southcentral Arizona.  With plenty of heating, it will be an active day over the higher terrain.  What about lower elevations?

Later in the afternoon, Tucson is forecast to have over 1000 J/kg of CAPE and a PW of 39mm.  Unfortunately, observed PW has dropped to 35mm at Tucson and 34mm at Amado.  We'll have to wait and see if this is a temporary dip or if the drying trend continues.  If it continues, it's likely that the runs will be too active.  Mid-level winds pick up speed and become more favorable for steering storms into the lower elevations.

All runs are nearly identical as they develop scattered storms over the high terrain of much of eastern Arizona by early afternoon and generally move to the west.  A few of these storms move close or into the Tucson area.  This is likely to be too much if the PW continues to drop.

Activity moves into central Pima County and into Mexico by late afternoon.  I'm confused why the WRF runs don't have more activity considering CAPE is so high.  Maybe it's that warm layer around 6-500mb capping deep convection?

500mb temperatures are high at around -5 to -3.   It seems there is always something that screws up a good looking situation.

Day 2
The surge continues and even moves into SW NM.

CAPE is again forecast to be high over much of eastern Arizona with some areas approaching 2000 J/kg.

Hot air continues in the mid-levels over SE Arizona, but there is slight cooling over SW NM.

Like I said earlier, it's always something.  The Tucson forecast Skew-T has good CAPE, shear, and steering, but a shallow mixed layer with inversions at the top of the lowest mixed layer and at 500mb.

With better moisture and lower mid-level temperatures, SW NM is very active with some strong storms.  Scattered deep convection is also over the Rim and White Mountains.

A few strong storms move into far SE Arizona during the early evening.

A big wind event for the Lordsburg Playa looks likely.