20160723

Previous Day
Yesterday's forecast hinged on whether IPW was going to stay in the upper 20's like the WRFRR or increase into the low 30's like the WRFNAM/GFS.  It remained in the 20's thus there was very little activity around Tucson.  Two wins now for the WRFRR around the Tucson area.

Initializations
A large MCS is dissipating over northern Sonora with some clouds drifting into SW Arizona.  Other than that, it's clear across the state and same with the model initializations.  500mb map indicates a weak IT between Flagstaff and Phoenix.  The upper IT appears to be located over Sonora and is quite weak.  There are 2 500mb centers with one west of LA and the other over eastern NM.  All three of the 12Z models initialize all these features as well as initializing IPW well.

Day 1
A strong outflow surge has moved into SW Arizona, but is fairly shallow as the IPW is only 36mm at Yuma.  It has helped to increase IPW over much of the state since yesterday.  The WRFNAM looks too wet by afternoon whereas the other two models have about 5mm less IPW.

This difference in forecast IPW has a large impact on CAPE as the WRFNAM has around 1000 J/Kg this afternoon while the WRFGFS has only a few hundred.  Steering continues to be marginal with only 10-15 knots from the east/southeast.  Low level winds are about 10 knots so there is a bit of shear present.

Very little deep convection occurs during the afternoon.  The WRFNAM is the middle of the road and develops a few storms in far eastern and southeastern AZ.  Storms continue along the border into the evening.

Day 2
The forecast track for Frank has moved a bit to the west and doesn't come quite close enough to trigger a strong gulf surge or Frank may just not be strong enough.  However, moisture has increased all along the GofC and into Arizona by 12Z.

By 21Z, a weak surge is underway with a classic fanning out of the winds across southern Arizona. Low level winds were not as strong as earlier predicted, but still should be strong enough to provide low level convergence when outflows from the east move in.  IPW is more than enough in the lower deserts.

What puzzled me yesterday was the lack of low level cooling in the model runs as typically a big surge cools down the PBL over the lower deserts and frequently it is the day after the surge that is the big day.  The model forecasts now look more like I'd expect with a significant inversion on top of the cooled PBL which is going to be the big problem.  Tucson has OK winds with some shear.  500mb winds continue to be weak.  Plenty of CAPE.  Strong low level convergence is going to be required to realize deep convection.

Deep convection is slow to get started and by 5pm there are scattered storms moving westward from eastern and southeastern Arizona.  The WRFGFS has a bit more coverage.  Hopefully, storms will be strong enough to generate good outflows.

The WRFGFS does generate strong outflows that move towards both Phoenix and Tucson.

However, there are no intersecting outflows thus only scattered weak convection forms.  A MUCH different forecast than yesterday, unfortunately.  Forecast confidence is low for Day 2 so perhaps tomorrow's model runs will again be different.  As the WRFGFS below is the best case, and that the model runs have been predicting too much convection  in general, doesn't give me much hope for tomorrow.