June 28th, 2024: Slight Increase in Storm Coverage In SE AZ Today

 Synopsis

The mid level subtropical high will remain centered near the AZ/MX border today with weak westerly flow over AZ. Still plenty of moisture and instability in place to produce scattered showers and thunderstorms mainly in SE AZ this afternoon and evening. A slightly better chance for a few cells in Tucson this afternoon due to a combination of high DCAPE (better outflow boundary potential) and weak upper level divergence. Main impacts from storms will be lightning, gusty winds, blowing dust, and brief heavy rainfall.

Current Conditions

The mid level anticyclone remains anchored near the AZ/MX border this morning with weak westerly winds aloft over AZ.

SPC 500mb analysis as of 16z this morning.

The only change to the synoptics today is a weak, subtle region of upper level divergence indicated by SPC 300mb analysis this morning.

SPC 300mb analysis as of 16z this morning.

This region of divergence is associated with the right entrance region of a 300mb speed max over the Four Corners. 

The 12z TUS sounding this morning indicating a relatively poor thermodynamic profile with around 500 J/kg of CAPE, around -200 J/kg of CIN, and a more pronounced subsidence inversion just above 500mb.

12z TUS Sounding courtesy of the SPC.

Still have plenty of moisture though with pwats hanging around 1.50 inches. 

Today's Forecast

 

Synoptics

The synoptics are a bit ambiguous today with the close proximity of the 500mb high promoting subsidence (descent) and a region of divergence at 300mb promoting ascent. The 500mb high will remain anchored near the AZ/MX border through this evening, but the region of upper level divergence over Central AZ will move east into SE AZ this afternoon. 

12z GFS 300mb winds valid this afternoon at 2PM MST courtesy of Pivotal Weather.

This is a very subtle region of upper level divergence, but it could aid in allowing more updrafts to breach the region of subsidence in the mid levels.

Thermodynamics

Mostly clear skies this morning across the state, so shouldn't have any issues with surface heating. In fact, SPC mesoanalysis of CAPE and CIN as of 10:00AM MST showing CAPE between 1000 and 2500 J/kg (increasing southeastward) and rapidly decreasing CIN across SE AZ. 

SPC mesoanalysis of CAPE and CIN as of 10:00AM MST this morning.

Sufficient insolation should allow low and mid level lapse rates to steepen throughout the morning and into the afternoon which should help marginally erode the subsidence inversion at 500mb. The 12z KTUS WRF-HRRR sounding forecasting around 1000 J/kg of CAPE and around 1500 J/kg of DCAPE by this afternoon which is nearly identical to conditions yesterday.

12z KTUS WRF-HRRR sounding for this afternoon at 2:00PM MST.

What to Expect/Impacts

Thermodynamics are nearly identical today compared to yesterday, but the synoptics have changed in which mid level subsidence is a bit stronger, and there is a weak region of upper level divergence. Ingredients favoring storms to reach Tucson today is sufficient buoyancy, weak upper level divergence, and DCAPE over 1500 J/kg to produce outflow boundaries. However, if subsidence remains too strong and/or anvil cloud cover develops CIN this afternoon, then convection could be suppressed in lower elevations of SE AZ. CAM solutions are more bullish with coverage of storms today compared to yesterday with both the 12z and 15z WRF-HRRR solutions forecasting storms to make it into Tucson late this afternoon and early evening. 

12z (left) and 15z (right) WRF-HRRR simulated reflectivity for 5:30PM MST this evening.

My forecast probabilities would be 40% to 60% chance of storms in Cochise and Santa Cruz Counties (highest probs over higher terrain), and between 20% and 40% in Eastern Pima County (including Tucson) this afternoon and evening. CAMs have also hinted at the potential for a few isolated, short-lived showers/storms in Pinal and Maricopa County (including the Phoenix vicinity) this afternoon/evening, but I would place probabilities below 20% in those areas. 

Main impacts from storms will be lightning, brief heavy rainfall, and locally gusty winds and blowing dust. 12z HREF has between 50% and 70% probabilities of 4-hour max wind speeds in excess of 30 knots in Cochise and Eastern Pima Counties with greater than 70% chance near the International Border.

12z HREF probability of 4-hour max wind speed greater than 30 knots for 5:00PM MST this evening courtesy of SPC.

WPC has SE AZ in marginal risk for excessive rainfall, but considering a drier boundary layer and mainly short-lived updrafts excessive rainfall is unlikely. However, isolated flash flooding is always a possibility.

Expect hazardous traveling conditions this afternoon and evening especially along I10 between Tucson and the AZ/NM Border as well as along I19 with the main threat being reduced visibility from blowing dust. If convection occurs in Tucson, the evening commute will be impacted with main impacts being reduced visibility and slick roadways.

Temperatures will be similar today compared to yesterday with high temps near 100 degF in SE AZ and between 105 and 110 degF in the lower deserts between Phoenix and Yuma.

12z WRF-HRRR 2-meter temps for this afternoon at 3:30PM MST.

This Weekend

The synoptic upper air pattern will change significantly this weekend as the subtropical high rebuilds into New Mexico with southeasterly flow aloft developing over AZ. In addition, a weak wave will move northwest in AZ tomorrow (likely an MCV associated with overnight activity in Sonora) transporting additional moisture into the region with pwats increasing to between 1.50 and 1.75 inches across the Southern half of the state.

12z GFS 500mb absolute vorticity for tomorrow at 5:00AM MST courtesy of Tropical Tidbits.

12z WRF-HRRR total precipitable water for tomorrow at 11:00AM MST.

Tomorrow looks to be a tricky forecast as the aforementioned wave coming up from Sonora looks to bring in some mid level debris clouds which CAMs have been hinting at.

12z WRF-HRRR simulated cloud top temperature for tomorrow at 11:00AM MST.

Will need to keep an eye on this to see if it verifies as a lot can change over the next 24 hours. Currently, it looks like significant activity isn't likely until Sunday and early next week. Stay tuned!