20220630

Previous Forecast

All good things must come to an end.  WRF had been doing well this monsoon season until yesterday as the forecast didn't go as planned for the Tucson or Phoenix area.  It went off the rails early as widespread strong storms developed to the west of Tucson by early afternoon, resulting in a cooling outflow and anvils overspreading the valley.  As the forecast for Phoenix was contingent on big storms moving from Tucson up I-10, that didn't work out there either.  Besides those two areas, WRF did a reasonable job, except for precipitation amounts.

Discussion

The monster CONUS anticyclone continues and is centered over Kansas.  A weak trough is present over the SW US, resulting in weak southwesterly winds over the northern 1/2 of the state.  500mb temperatures are still quite cool, around -7C.

The morning soundings indicate only a limited amount of CAPE.  Phoenix exhibits a "green onion" profile indicating a worked-over atmosphere, despite storms mostly staying out of the metro.  Tucson isn't worked over, but MLCAPE is essentially zero, despite a nearly saturated "heavy rain" profile above 700mb.  PW is relatively high at Tucson, with a peak of 41mm around 12Z.  The Phoenix wind profile is mainly unidirectional from the SW.  Tucson is a better, with southwesterlies above 500mb and southeasterly 10-15 knot steering flow.

Initializations

A weak MCV was noted near Flagstaff, moving northeast.  WRF, to its credit, did spin up a similar feature yesterday.  There is a much larger MCV over central Sonora as there was a large MCS yesterday and last night.  Widespread clouds are associated with both features.  All initialized the Arizona MCV OK.  Only the RR did a fair job with the Sonoran MCV.  The 6Z GFS initialized clouds well.  The HRRR didn't have enough, especially in Mexico, and some RR initializations had too much.  The GFS and 15Z RR appear to be the better initializations.

Day 1

An outflow-induced Gulf Surge appears to be underway as Yuma has 15 knot SE winds and a dewpoint of 70F.  It looks quite shallow, as PW has increased only slightly.  Moisture continues to advect into Arizona during the day, keeping PW in the mid-30 mm range.

850mb dewpoints are also relatively high, at around 10 to 12C.

Lastly, CAPE is moderate, mainly over southeastern Arizona, so that looks like the favored area today.

Deep convection develops during the afternoon, mainly over the higher terrain from Flagstaff eastward and over the higher terrain of SE Arizona.

Tucson has just enough CAPE to support some deep convection, but there are issues.  The first is that the wind profile becomes mainly southwesterly, with minimal steering flow.  The second is a bit of an inversion on top of the mixed layer.  Also, note the double structure of the mixed layer, with a wetter layer (due to the surge) below 850mb.  This could also impede mixing to the LFC.

Most morning runs develop strong to isolated severe storms over far southern Arizona by early evening, but most stay out of the Tucson valley.  Still, with a strong enough outflow, there is enough CAPE to support a few storms.

Phoenix has just enough CAPE to also support a few storms.  Like Tucson, the vertical wind profile is poor, and the PBL needs to mix quite a bit higher for storms, so a strong OFB will be required for widespread deep convection.

Some activity to the north of Phoenix this evening, resulting in some outflow boundaries moving into the valley.  Some runs develop a few storms, similar to last night.  The best is the 15Z RR which has a few strong storms in Phoenix later this evening.  Hope for the best!

Day 2

As very dry air moves into western Arizona, a distinct drying trend begins for the state.  Dry air is also developing over southern NM.  Elsewhere, moisture continues to advect into the state due to an ongoing Gulf Surge, perhaps driven by another MCS in Sonora.

CAPE is forecast to be higher from southern Arizona to the Grand Canyon, so expect considerable more activity in these areas.

Maybe Tucson gets their first big storm event? 

Some runs move activity north along I-10 and into Phoenix during the early evening hours.  We've heard this story before, and it was an unhappy ending last time.