20220809

Previous Forecast

It was a quiet day and early evening for the lower elevations, but that changed after sunset when storms developed over Cochise County and moved into the Tucson area.  As expected, most activity stayed over the higher terrain, but parts of Tucson nearest the Catalinas got over an inch.  Storms moved their way to Phoenix but died out as they moved in.  A few places on the east side got a lot of rain.

The forecasts were pretty good around the Tucson area but didn't have enough activity move up into Phoenix. 

A forecasting tool that is never mentioned by other forecasters is the GPSIPW data.  If WV increases, moisture convergence/advection is underway, and precipitation is likely.  WV goes down, dry advection, dry air entrainment, etc..., probably nothing.  Last night's plots were a great example.

Discussion

The upper-air pattern remains about the same. There is an MCV just west of Phoenix, which can also be seen on the 500mb map.

The 300mb map has been more interesting due to all the ITs passing through.  Weak divergence/difluence is again present for much of Sonora and southern Arizona.   A large IT is located south of Brownsville and is partially responsible for the large MCS continuing over the far southern Gulf of California.

The MCS is of great interest as these typically trigger a Gulf Surge as a meso high sets up due to all the rain-cooled air.  With the heat low at the top of the Gulf, a pressure gradient sets up, and winds blow up into Arizona.  The question mark indicates a possible weak IT.  Not much was seen on the maps, but WV imagery shows some rotation.

The soundings are worked over in both Tucson and Phoenix.  Mid-level steering is not very good at Tucson, probably due to the influence of the MCV.  As it moves away, winds should turn back to easterly.  The profiles look similar to yesterday, with no MLCAPE, but like yesterday, with some heating, the atmosphere can recover, and evening storms are again possible.

Another informal tool I like to use for determining where storms will go is the previous day's lighting plot.  Locations that had a lot of lightning also had a lot of rain.  This cools down the ground, and much of the next day's heating goes into evaporating water (latent heat) rather than heating and destabilizing the atmosphere(sensible heat). Those areas in far NE Pima, SW Graham, should have less activity if this works out.  Alternatively, the rest of Pima and Santa Cruz should be active.

Initializations

I've seen more difficult initial conditions.  Showers and clouds are decreasing, except for the MCV near Phoenix.  It's mainly clear elsewhere.   The 6Z HRRR wasn't too bad but didn't have enough clouds, but it did have the MCV.  The 6Z GFS was poor as it missed the MCV and didn't have enough clouds.  9Z RR and the 12Z initializations were good.  The RR kept convection going around the MCV a bit too long.

Day 1

A weak Surge gets underway this afternoon, but we already have more than enough moisture.  It also continues to be moist in the SE flow out of NM.

It's the same story at 850mb.  Note the dry area near Phoenix associated with the remnant MCV.

From the CAPE forecast, the active areas will be SW NM and over to western Pima County.  Another active area is northwestern Arizona, assuming it can clear up and recover from all the morning activity.

Most runs agree on developing strong storms over Santa Cruz and southern Pima this afternoon.  Some runs have strong/severe storms in NW Arizona (HRRR) while others (RR) don't, as it didn't clear up enough.

Despite being worked over, Tucson manages to fully recover. By afternoon, 900-1100 J/kg of CAPE is present, along with a favorable wind profile, except for the anvil level as winds are 20 knots from the east, so anvil shading could be a problem.  However, with storms developing to the south first, no problem!  Tucson is mixed relatively deeply, and only a weak cap is present.

There is a bit of upper support as well.  Weak divergence/difluence is over much of Sonora and southern and central Arizona.

All runs have some deep convection in the Tucson area by late afternoon.

Wet microbursts will likely create a few areas of severe winds in Tucson this afternoon.

Flash Flooding in Pima and Santa Cruz Counties is a risk, especially for the Catalinas, if it rains again.  2" last night.

During the evening, storm activity moves to the WNW and approaches Phoenix.  

It's not looking good for Phoenix.  CAPE is marginal at 700 J/kg, and there is a cap present.

Phoenix was 0 for 4 for the last four WRF runs.  The best they could do was a weak storm or two and some rain.  It looks like another casino flooder for Vegas.

Supercells in eastern WA/OR today!

Day 2

Well, so much for a surge beginning as winds are mainly light and variable tomorrow.  Plenty of moisture remains, though.

CAPE generally increases, so there should be more activity, especially for SE and SC Arizona.

The 250mb pattern is hugely amplified with a west coast trough forcing the anticyclone center far to the north, over WY!  Of great interest to Arizona, an IT is moving through, providing good upper-level support for storms.

More storms for Tucson and maybe even Phoenix.

Supercells look likely for NV and ID tomorrow.