20190721

Initialization
The discussion today is mainly for tomorrow plus I got a very late start, so I'm not going to say much about the initializations. A quick look indicates that they all look quite good as the situation is straightforward.

Day 1
Moisture has returned to much of southern Arizona due to a gulf surge as PW has increased into the 35 to nearly 40mm.  This surge event has been forecast by the models for the past few days.   The surge continues into this evening while another area of moisture is moving west from NM and the combination will play an important role in our weather tomorrow.

It is already quite active in far south-central Arizona which was well forecast by both the morning runs and from yesterday.   Generally, all the model run continue this activity into the early evening hours with little or no activity for the lower elevations.

Day 2
Finally, it looks like the first big day, especially for the Tucson area.  The surge weakens somewhat, but PW continues to be fairly high from the 35 to nearly 45mm over the lower deserts.  Of great interest is the low level, and for once, moist easterly flow.  This sets up a low-level convergence zone over southeastern Arizona.

850mb Td plot has a similar convergence zone.  850mb Td is also favorable, above 10C.

Mid-level winds were light and variable today, but by tomorrow,  10-20 easterly flow is over southern Arizona, favorable for storm propagation

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Another positive is there is some upper support as at  250mb, there is an area of difluence with weak divergence present.

CAPE looks excellent as many areas are 1000 to above 2000 J/kg. 

All runs develop storms over eastern and southeastern Arizona during the afternoon hours. 

The forecast Skew-T plot for Tucson is impressive and a classic looking profile for an active thunderstorm outbreak.  CAPE is around 1500 to maybe over 2000 J/kg,  the PBL is mixed deeply and an excellent wind profile with low-level shear, good mid-level flow.  There is a slight inversion at the top of the PBL, but with good outflow and some low-level convergence, this shouldn't be a problem.  Textbook!

The details are a bit different, but all the runs move big storms into the lower elevations of Pinal and Pima Counties during the late afternoon or early evening.   Some storms will have very strong to isolated severe winds. 

Phoenix is not looking good as the PBL isn't mixed deeply and is going to need more than just a linear outflow to provide enough lift for deep convection.

Storms generally die out as they move into Pinal county, while central Pima continues.  The 15Z WRFRR does eject a very strong outflow boundary into the Phoenix valley and even this isn't enough to trigger much activity beyond lots of blowing dust.  All the other runs have weaker winds.

Maybe because of the favorable upper support, showers and a few storms continue late into the night.