20220803

 Previous Forecast

Despite over 2000 J/kg of CAPE at Tucson at 0Z, no activity occurred up to 12Z.  During the day, storms stayed mainly over the higher terrain.  Later, a large MCS developed in northern Sonora, and some weak storms managed to form along its northern periphery.  While the MCS was predicted, the morning activity was not.  After I saw the 0Z sounding, I thought it might support morning elevated activity.

Storms started popping later in the afternoon here in Paradise, and this rotating tilted updraft appeared before me!  I had the sense to start taking a time-lapse posted on Twitter.

Discussion

The morning weather is dominated by residual elevated morning storms moving across Tucson and approaching Phoenix.  The 12Z sounding from Tucson shows part of the reason why and that is the Max Unstable level of 721mb.  The MUCAPE is 1470 J/kg, so no wonder activity is so robust.  This throws a giant spanner into the WRF forecasts from yesterday and perhaps today's runs as well.  Steering flow continues to be good at 20 to 25 knots, but anvil-level winds are still parallel to the steering flow. 

It is a similar story for Phoenix with a fair amount of elevated CAPE.  Perhaps there is enough to keep the approaching storms going later this morning.

For whatever reason, all of Mexico is missing, and only Tucson was plotted for Arizona on the SPC 500mb map, so I grabbed this one from PSU.  A broad ridge dominates the southern CONUS, with the center located somewhere around the Four Corners.  It's still warm, with temperatures around -4 to -6C.  The MCS is not resolved in the upper-air data and a broad but weak IT over central Mexico.

At 300mb and seen in the GOES WV imagery, an upper-level IT is located just south of the Big Bend and appears partially responsible for the giant MCS and maybe the ongoing Arizona activity.  A streamline analysis indicates difluence/divergence for much of southern Arizona.

GPSPWV and surface observations indicate an outflow surge is underway.  PW has increased in the Phoenix area to around 43mm, while Puerto Penasco is up to 48mm.  SE Arizona is also very moist, with PW in the 40-45mm range.

Initializations

Considering the complexity, most initializations are accurate except for the 6Z HRRR.  All the others had some amount of morning showers/storms/clouds.  The 12Z RR seems to have too extensive clouds, but the 6Z GFS, 9Z RR, and 12Z HRRR look good.  They all have the MCS circulation initialized fairly well too.  However, there appears to be a small MCV around the Tucson area, which is responsible for all the morning activity, and this minor feature is not well initialized.  As it is a complex situation, I decided to peek at the PW initialization, and it's remarkably good, especially the 12Z HRRR.  This situation would have resulted in significant PW initialization errors a few years back.  Not anymore, as NCEP PW assimilation and initialization have really advanced.

Day 1

The Surge is forecast to become quite deep, with the classic clockwise spiral over the southern 1/2 of the state.  Dewpoint temperatures are in the sweet spot of around 12C.  Higher and storms fire off too early and result in a lot of debris clouds. 

While 850 looks pretty good, the CAPE forecast for Tucson and Phoenix does not, which isn't surprising due to the ongoing activity there.  The 12Z WRFRR is the most pessimistic and only has decent CAPE over far southeastern Arizona.

Not surprisingly, both the WRFHRRR and RR have minimal activity this afternoon.

The late afternoon Tucson Skew-T forecast tells the story of why, which is a cap on top of the moderately mixed layer.  There is good low-level shear and moderate steering flow, but the upper winds are still quite strong and parallel to the steering.  The good part is that CAPE is high, which will probably result in another situation of elevated nocturnal storms.  

The situation in Phoenix is a bit worse as there is a strong subsidence inversion in the mid-levels.

At 250mb, the weak IT moves WNW slowly, with a weak jet streak over northern Sonora and Chihuahua and into southern Arizona, resulting in a bit of influence and divergence over the south of 1/2 of the state.

By this evening, storms finally get going over southeastern Arizona.  Some are likely to be severe, with severe winds due to wet microbursts.

CAPE manages to increase over the lower deserts later in the evening, so storms for both Tucson and Phoenix are possible.  I'm not sure about this forecast as Tucson and Phoenix still have considerable showers and storms at 17Z.  The model forecasts had wound down the activity and had cleared by this time.  Tucson is getting close to clearing out, though, so who knows?

By later in the evening, large areas of strong to severe storms are over southeastern Arizona and trying to move into Tucson.  Some model forecasts spin up an MCS, increasing the likelihood of storms in the lower elevations.  The WRFHRRR brings storms close to Tucson, but they weaken as they move in.

The 12Z WRFRR (and earlier runs) bring storms into Tucson.  As the model runs cleared out too early, this may be too aggressive.  Hopefully, the 15Z runs initialize well and help nail down what happens tonight.

All runs have some activity in or near Phoenix during the early morning hours.  The intensity varies from showers and weak storms to strong storms.  

Day 2

Despite all the activity, the forecast calls for moderate to high CAPE for much of the state.  I'm not so sure about that.

If there is this much CAPE, it will be challenging to get storms to go in the lower deserts due to the strong cap on top of the mixed layer.

Another negative is the IT lifts out, resulting in confluence/convergence over southern Arizona.  Plus, the old rule of after a big event, the following day is a down day.