20160801

Previous Day
I initially though the 12Z model runs were going to do fairly well, but by 17Z it became clear that they were going off the rails.  The models heated up southern Arizona too much and this resulted in widespread strong storms over southern Pima and Santa Cruz which then moved slowly northward into Pinal county by early evening and then ejecting outflows into Phoenix which intersected with strong outflows from the north and triggering additional deep convection.  None of this happened.  Phoenix is always tough as everything has to go right elsewhere for and active night to occur.   I initially thought that Tucson was unlikely to see much activity as the airmass was cooled too much and there wasn't enough heating.  That was also wrong as there was just enough heating to mix to near the LFC (0Z sounding) then the MCS from Cochise county moved in with strong outflow and set off widespread storms.  The 15Z WRFRRx did have the situation correct around Phoenix as storms remained just to the north and west but missed the MCS over SE Arizona.  The WRFNAM had the Cochise county MCS, but didn't move it into eastern Pima.

15Z WRFRRx

Initializations
It's going to be a tough day forecasting as the situation is complex with the IT located  over western Pima county.  All 12Z initializations are correct.  Widespread clouds and some showers and thunderstorms are ongoing over much of southern Arizona.  The clouds are breaking up in some areas, while other areas are seeing thick clouds continuing.  As expected, the model runs are struggling with the WRFRR being least bad.  The other two have it almost clear by 17Z!

All three have initialized IPW well.  That isn't going to make up for the major cloud and heating errors as at last look, Tucson was running 5-8F cooler than the model runs.  Combine this with the issue with clouds, model confidence is low.  They should work better in central and northern Arizona where errors are smaller.

Day 1
IPW is about as high as it gets here as Tucson has 45mm and Phoenix has 50mm.  Afternoon values don't change much and the surge has weakened.   850mb Td continue to run very high with 14-15C.  Again, another possible 'too wet to rain' situation. 

500mb temperatures have warmed over the past day and are now around -6C.  The IT is mainly stationary over western Pima county with southerly or SE flow.  Not the best, but it could be worse.

CAPE has decreased as mid level temperatures have increased.  Moderate to high CAPE is forecast mainly in far SE Arizona.  Showers and some weak storms are ongoing in that area.

There is just way too much heating in the model runs, especially the WRFGFS. 

WRFGFS

I'm going with the 12Z WRFRR and the 15Z WRFRRx, which is just started running as of this writing.  Scattered activity over the Rim and White Mountains this afternoon with isolated storms over SE Arizona, mainly where the sun can break through.

15Z WRFRRx

Very wet at Phoenix this evening with 50mm of IPW.  However, warming aloft and cooling at the surface result in minimal CAPE and a somewhat shallow mixed layer.  Steering winds are quite favorable and this is the wildcard as storms may be able to move into at least the far east part of the valley at some point during the evening. 

That's not forecast by any of the morning runs except for the WRFGFS which has been notoriously overactive.  A few storms may slip off the high terrain over western Arizona down into La Paz county later this evening. Some of the model runs are showing some early morning activity around Maricopa and Pinal counties.  Certainly, with such a wet atmosphere, around 600 CAPE present, and the mid-level low lurking, deep convection could develop.

Day 2
Again, in this environment, Day 2 forecasts are not worth much. 

The mod level trough continues to wander about over SW Arizona into far NW Sonora.  Steering flow is mainly weak and from the east and temperatures are around -6C.

 Very wet air remains over the state.  Again, widespread clouds are likely with such wet air and it may again be 'too wet to rain' for the Tucson and Phoenix areas.