20200701

Discussion

Moisture is increasing over the southern 1/2 of the state due to a weakening tropical system located to the southwest of the southern tip of Baja.

This isn't a traditional monsoon pattern as south-westerlies dominate over the southwestern CONUS.  The semi-permanent trough continues over the NW CONUS, keeping the monsoon ridge to our east, over southern Texas.  We're just lucky that this early season tropical system moved far enough north resulting in the advection of wet air into Arizona.

Day 2

Moisture advection continues overnight and by tomorrow morning, PW is quite high over much of southern Arizona.  There is a lot of wet air to our south as Suominet PW sites in Sonora have reported over 40mm this afternoon.  

In spite of the high PW, CAPE isn't very impressive with only around 500-1000 J/Kg over far southern Arizona.  The model runs have been waffling back and forth with regards to the CAPE forecast.  Previous runs before 12Z were quite low thus it's possible that CAPE could end up being less.  

A weak trough is present over southern Arizona tomorrow, which results in weak southeasterly mid-level flow thus winds are not unfavorable for steering storms off of the higher terrain towards lower elevations of far southern Arizona.  

The Tucson Skew-T forecast indicates 3 to 500 J/kg of CAPE which should be sufficient to support a few storms in the Tucson area.  The mixed layer is quite deep by early to mid afternoon, and near the LFC so storms should start forming over the higher terrain around that time.  As the sub cloud mixed layer is quite deep, strong winds are possible with a few storms.

The various 12Z runs more or less have the same idea of developing scattered storms over southern Arizona tomorrow afternoon.  Timing and location are quite variable, however.  The WRFRR moves an area of storms into the Tucson during the late afternoon.  

The main threat will be strong winds as a few areas may see gusts above 50 knots.  As PW is pretty high, a few storms may produce some heavy rain too.

A few storms may move into Pinal County during the evening.

Below is a 4-panel plot of the most recent runs showing that there could be > ,5" of rain in some places.  Hopefully over the Bighorn Fire!