20220714

 Previous Forecast

The higher elevations of south-central Arizona had quite a bit of precipitation, and these storms eventually moved and/or generated OFBs that moved into the southern Phoenix area.  Some parts of Tucson got a bit of rain.  Another large MCS impacted Sonora during the evening hours.  EMX could see the storms, and the tops were >70k feet at one point.  The outer domain of many of the runs was able to forecast the MCS.

Some runs, like the 12Z GFS, did forecast activity in the Phoenix area, and many were able to forecast the northern extent of the Sonoran MCS.

Discussion

The 500mb anticyclone remains in the Four Corners region, providing good easterly to southeasterly steering flow.  Temperatures have increased a degree or two and range from -5 to -6C and are becoming less favorable for deep convection as the anticyclone slowly strengthens.

No interesting features at either 500 or 300mb.  However, a jet streak is moving down the back side of the east coast trough, which may break under the ridge and set up some nice upper-level divergence over Sonora and southern Arizona in a few days.

PW is mostly the same for most locations.  It has increased over far southeastern Arizona and the Phoenix area.  An outflow surge is underway at Yuma, but it looks quite shallow.   Phoenix has around 40mm of PW and about 300 J/kg of MLCAPE, which is better than zero CAPE.  The wind profile is not as good as it's generally southeasterly throughout the troposphere.  Perhaps the low-level winds will become westerly later due to the surge.

Tucson looks about the same-limited CAPE and mainly easterly flow.  Without more CAPE, significant deep convection is unlikely, again!

Initializations

Scattered to broken debris, clouds are over much of Arizona.  It appears there is a weak MCV to the southeast of Puerto Penasco and maybe another over far west-central Arizona.  Cloud initialization was good by the HRRR and GFS.  The RR has been struggling lately, and the 9 and 12Z are especially bad today as they have widespread clouds and precipitation. The initializations were mostly missing the probable MCVs, but that's OK as they are far enough west to not be a factor.

Day 1

The weak outflow surge continues into the afternoon, increasing PW mainly for southwestern Arizona.

850mb dewpoints are pretty good for western and central Arizona, around 10-14C.  Some dry air advection continues over eastern Arizona.  I'm afraid to say that this is starting to look like the 2020 season when subsidence and dry air advection from NM dominated.

CAPE continues to be marginal for much of the state, except for southwestern Arizona.  Again, storms will struggle when moving into the lower elevations.

Deep convection initiates over the typical high elevations of the state by mid-afternoon, except for far SE Arizona.  Storms develop over the higher terrain of eastern Pima County, and most of the model runs move them into the Tucson area by later in the afternoon.

The Tucson forecast Skew-T looks pretty good, for once, as CAPE is around 700J/kg.  Low-level NW flow even kicks in to provide additional moisture and shear.  Upper tropospheric winds are light and variable, so anvils shouldn't move out ahead of storms much, especially considering steering flow is quite strong at around 20 knots.

Phoenix looks favorable for storms as well.  Most model runs have CAPE around 1000 J/kg by late afternoon and a surge signal present: low-level southwesterly winds and increased dewpoints.  The PBL isn't mixed very deeply, but OFB collisions should provide enough lift to trigger deep convection.

There is a remarkable consistency between the runs as they all move the eastern Pima County storms down I-10 towards Phoenix.  All but the 12Z WRFHRRR moved these storms into the Phoenix area this evening.

Day 2

Subsidence and dry air advection dominate eastern Arizona, while moisture generally decreases over western Arizona as the surge weakens.  Very 2020 looking :(

CAPE is sufficient for most locations, excluding SE Arizona, for storms.

Most activity is restricted to the higher elevations.  Strong to Severe storms form over central Pima County due to the high CAPE located there.  

Phoenix manages to hold on to decent CAPE, and the wind profile looks favorable, so it's not out of the question that storms could develop.  Most runs don't do this, though, due to a lack of OFBs and the old rule of the next day after an active day is down.