August 22nd, 2024: Clouds Won't Be A Problem Today!

 Synopsis

Mid level flow is gradually turning southwesterly today as a mid latitude trough deepens along the West Coast. A subtle, embedded shortwave is forecast to lift northward across the Eastern half of Arizona this afternoon/evening and combined with sufficient thermodynamics will support a chance for showers and thunderstorms across the region (including Tucson and potentially Phoenix). Main impacts from storms today is strong wind gusts, blowing dust, and heavy rainfall which could lead to localized flooding.

Current Conditions

Mid level water vapor imagery this morning showed a high amplitude ridge over the Great Plains, a plume of moisture across the Eastern half of Arizona, and drier air beginning to move in from the southwest.

Mid level water vapor imagery as of 9:45AM MST courtesy of College of Dupage.

Arizona remains in between two large synoptic scale features which are a deepening trough off the West Coast and a subtropical ridge over the Great Plains.

12z GFS 500mb analysis this morning courtesy of Tropical Tidbits.

In addition, the cyclonic vorticity associated with the inverted trough which has influenced our weather the past couple days is lifting northward and becoming embedded within the broad mid latitude trough pattern. 

Moisture is relatively more evenly distributed across the state as indicated by current SPC mesoanalysis.

SPC mesoanalysis of precipitable water valid for 10AM MST this morning.

Today's Forecast

Synoptics/Dynamics

Mid level flow will remain southerly/southwesterly across the region today as Arizona will remain in between a deepening trough to the west and a high amplitude ridge to the east.

12z GFS 500mb cyclonic vorticity valid for 11AM MST today courtesy of Tropical Tidbits.

Also, an embedded shortwave will lift northward across southeast Arizona this afternoon providing some marginal dynamic forcing in the form of differential cyclonic vorticity advection (CVA). 

The best synoptic scale dynamics will remain in Northern Arizona due to upper level divergence within the right entrance region of a jet streak over the Intermountain West.

 

12z GFS 250mb winds valid for 11AM MST courtesy of Tropical Tidbits.

Thermodynamics/Wind Shear

We don't have any issues with widespread cloud cover today, so the surface should have no problem heating and consequently steepening low and mid level lapse rates by this afternoon. KTUS model soundings forecast between 750 and 1000 J/kg of Mixed-layer CAPE, minimal CIN, and near 1500 J/kg of DCAPE during the early to mid afternoon hours.

12z KTUS WRF-HRRR sounding valid for 2PM MST this afternoon.

Relatively unidirectional wind shear is forecast with only around 10 to 15 knots of speed shear. So not great but not terrible. 

Thermos are expected to be similar in Phoenix with model soundings forecasting just under 1000 J/kg of MLCAPE, minimal CIN, and near 1500 J/kg of DCAPE as shown below.

12z KPHX WRF-HRRR sounding valid for 3:30PM MST this afternoon.

The forecast vertical wind profile is marginally better in Phoenix though with a bit of veering in the lower half of the troposphere and slightly stronger speed shear. 

What to Expect/Impacts

With relatively favorable synoptic scale dynamics, modest wind shear, and sufficient thermodynamics, I'm expecting quite an active day across mainly the eastern half of the state which includes both Tucson and potentially Phoenix. Yesterday, morning CAM solutions didn't pick up on morning storm activity and persistent cloud cover which lead to a poor forecast and a model "bust" for at least Tucson. Today, I don't see any reason to not believe the morning CAM solutions as everything looks to be on track. 

Both the 12z and 15z WRF-HRRR forecast convection to impact the Tucson vicinity during the mid to late afternoon hours as shown below.

12z (left) and 15z (right) WRF-HRRR simulated reflectivity valid for 5PM MST this afternoon.

As the embedded shortwave moves northward this evening, could see some isolated/scattered storm activity in the Phoenix vicinity.

12z (left) and 15z (right) WRF-HRRR simulated reflectivity valid for 7:30PM MST this evening.

CAMs seem to keep the majority of activity mainly to the east of the PHX metro, but a few cells are possible especially if outflow boundaries can move through the area.

Extreme northern Arizona should be quite active (especially from Flagstaff northward) with SPC having a marginal risk for severe grade wind gusts and hail this afternoon. Also, due to better dynamics up there, excessive rainfall is possible and the WPC has that region in a slight risk today.

There aren't any SPC risks for Southeastern Arizona today, but strong winds, blowing dust, and isolated instances of hail are possible with any thunderstorm. The 12z HREF has 50% to 70% probabilities of 4-hour max wind speeds in excess of 30 knots (where dbz>20) across most of Eastern Arizona (including Tucson and Phoenix) this afternoon and evening.

12z HREF 4-hour max wind speeds and probabilities of winds in excess of 30 knots where dbz>20 valid for 5PM MST this afternoon courtesy of the SPC.

There is a chance of heavy rainfall which could lead to localized flooding in the Tucson vicinity today with the 12z HREF showing 30% probabilities of 3-hour precipitation in excess of one inch this afternoon and evening.

12z HREF 3-hour mean QPF and probabilities of 3-hour precipitation in excess of one inch valid for 5PM MST this afternoon courtesy of the SPC.

I would anticipate hazardous traveling conditions especially along the I10 corridor between the AZ/NM Border and Phoenix, the I19 corridor between Tucson and Nogales, and the I8 corridor between Casa Grande and Gila Bend. The evening commutes in the Tucson and Phoenix metros could also be impacted with main risks being reduced visibility and localized flooded roadways.

In general, expect an active day across much of Eastern Arizona with decent probabilities of storms in Tucson, and more isolated chances in Phoenix.