20220709

 Discussion

The 500mb anticyclone is centered over Colorado, resulting in favorable southeasterly mid-level flow over the state.  In addition, temperatures have decreased and are a favorable -7 to -9C.  At 300mb, a broad trough was seen over northern Sonora, resulting in some divergence over southern Arizona.  Satellite imagery shows the center to be over Baja California Sur.  There is an MCV or inverted trough over the northern Gulf of California, moving NW, so no factor for Arizona.

Moisture has increased over southeastern Arizona to around 30-32mm.  The Tucson sounding still doesn't have any CAPE, so additional moisture will be needed for activity there.  The lower troposphere is very dry.  The vertical wind profile looks good with strong ESE steering flow.  Upper troposphere winds are also mainly easterly but weak, so anvil shading shouldn't be much of a problem.  By the way, this is my definition of the monsoon start: when 300mb and above winds become easterly. 

Initializations

I wanted to mention my delight with the Mexican upper-air data being available just about every day this season.  As long-time readers may remember, Mexico had a lot of trouble with its upper-air stations for years.  Lack of personnel, no helium, running out of money, no sondes.  Worse, the vital station of Empalme (near Guaymas) was almost always missing.  Chihuahua City also fixed its problem with the heights.  They were consistently 20-30m too low last year.  It's mostly clear over the state this morning, and the initializations were the same, except for the 12Z RR. It had too many clouds over SW Arizona, which ultimately won't be a factor as they are moving away.  Not much CAPE is present over Arizona, NM, or Sonora.  Hmmm.

Day 1

The big question is, where will the moisture and instability come from today?  WRF develops an area of low-level moisture convergence between the drier easterly flow in NM and the weak westerly flow over SW Arizona.  

850mb dew-points are high enough, around 10C, to support storms, but not much precipitation is expected.  However, strong winds are a threat due to the drier air in the mixed layer.

All the runs have this moisture convergence, which increases CAPE over southeastern Arizona by mid-afternoon to around 500-1000 J/kg.  

CAPE is sufficient for some storms in the Tucson area later this afternoon.  The mixed layer is deeply mixed, and winds are favorable, with some low-level shear and good SE mid-level steering.  Based on the forecast Skew-T, it looks like storms in and around Tucson later this afternoon.

Strong to isolated severe storms develop over the higher terrain of much of eastern Arizona by mid-afternoon.

With the favorable ESE steering flow, storms move off the high terrain.  All runs have activity in the Tucson area by late afternoon and are remarkably consistent.

Outflow boundaries move WNW into eastern Maricopa and Pinal Counties during the early evening.  However, CAPE is nonexistent in Phoenix, so storms are unlikely to develop and move through.

Precipitation amounts are generally light, with amounts less than 1".  Note that all 4 of the most recent runs have some activity in Tucson.

Day 2

Moisture doesn't increase much for the lower elevations, but the higher terrain has sufficient moisture for storms.

CAPE continues to be marginal for lower elevations but sufficient for deep convection for the higher terrain of much of eastern Arizona.

Maybe a weak storm in and around Tucson?