August 8th: Better Chances for Thunderstorms in Tucson Today and Tomorrow

 Synopsis

Better chances for showers and thunderstorms in Tucson this afternoon and evening as well as tomorrow. Temperatures will remain below 110 degF across the lower deserts today and tomorrow due to falling mid level heights and ample amounts of low level moisture.

 Current Conditions

Radar and visible satellite imagery early this morning showed a few showers and thunderstorms over the Phoenix metro as well as isolated debris clouds across southeastern Arizona. 

Visible Imagery loop this morning courtesy of College of Dupage.

Observations at the Phoenix Sky Harbor reported a trace of precipitation with a few other gauges around the Phoenix metro reporting anywhere between a trace to a couple tenths of an inch. At this point, any rainfall is welcome in the Phoenix metro as this monsoon season has not been too kind to that area thus far.

There is still plenty of moisture this morning with SPC mesosanalysis showing precipitable water ranging from 1.1 inches in far southeastern Arizona to 1.5 inches in southwestern Arizona. 

SPC mesosanalysis of precipitable water as of 17:00Z this morning.

  

The 12z TUS sounding also displays sufficient thermodynamics with pwat at 1.51 in, a surface dew point of 62 degF, and MUCAPE of 1396 J/kg. 

12z TUS sounding courtesy of the SPC.

Regarding synoptic conditions, SPC 500mb analysis displays the mid level anticyclone centered over western Texas this morning with southwesterly to westerly winds aloft over Arizona. 

SPC 500mb analysis at 1700Z this morning.

At 300mb, there is still some speed divergence, primarily over central and Northern Arizona, which was the the primary lifting mechanism responsible for the thunderstorm activity around the Phoenix metro this morning.
 

Today's Forecast

Synoptic Conditions

Marginally favorable upper level conditions at 300mb are expected to continue throughout the day with eastern Arizona remaining in a region of speed divergence aloft which will act as some synoptic scale support today. Speed divergence increases from south to north across the eastern half of the state with east-central and northeastern Arizona in the better region of ascent compared to southeastern Arizona.

12z GFS 300mb heights and winds for 18z today.

The mid level anticyclone has weakened a bit since yesterday with 500mb heights falling to between 592 and 594 dm across Arizona. Even though the high has weakened, southeastern Arizona will be under the influence of weak anticyclonic vorticity advection which will act as an inhibiting mechanism for convection this afternoon. 

12z GFS 500mb heights and vorticity for today at 18z.

Thermodynamics

The 12z KTUS WRF-HRRR model sounding forecasts plenty of moisture and CAPE by early this afternoon when CAMs forecast convective initiation. With 1.53 in of pwat and 1922 J/kg of CAPE expected by early this afternoon, thermodynamics are most definitely sufficient enough to initiate and sustain thunderstorms in Tucson.

12z KTUS WRF-HRRR sounding for 1:00 PM MST this afternoon.

What to Expect

There is significant consensus in our WRF runs as well as the raw HRRR that convection will initiate over the Tucson mountains early this afternoon and move through the Tucson metro between 2:00 PM MST and 6:00 PM MST with the 15z WRF-HRRR being the only outlier. The 15z WRF-HRRR forecasts convection to initiate over the Santa Catalinas and Rincons early this afternoon leaving the Tucson metro dry. However, I checked the raw 15z HRRR, and it shows convection developing over the Tucson metro. Also, recent runs of the HRRR (16z and 17z) forecast convection over Tucson this afternoon. Considering this, will disregard the 15z WRF-HRRR forecast. The only mechanism that has the potential to inhibit convection  today is the anticyclonic vorticity advection at 500mb, but am thinking speed divergence at 300mb combined with decent thermodynamics will be sufficient enough for convection in the Tucson metro this afternoon. Below is the forecast evolution of storms today in the Tucson area.

12z WRF-HRRR Tucson Area station plots and simulated maximum reflectivity for today at 1:00 PM MST.

12z WRF-HRRR Tucson Area station plots and simulated maximum reflectivity for today at 2:00 PM MST.

12z WRF-HRRR Tucson Area station plots and simulated maximum reflectivity for today at 3:00 PM MST.

12z WRF-HRRR Tucson Area station plots and simulated maximum reflectivity for today at 4:00 PM MST.

12z WRF-HRRR Tucson Area station plots and simulated maximum reflectivity for today at 5:00 PM MST.

12z WRF-HRRR Tucson Area station plots and simulated maximum reflectivity for today at 6:00 PM MST.

12z WRF-HRRR Tucson Area station plots and simulated maximum reflectivity for today at 7:00 PM MST.

Convection will continue to develop east of Tucson throughout the evening as WRF-HRRR has the most widespread and intense activity over the higher terrain east of Tucson.

12z WRF-HRRR simulated maximum reflectivity for this evening at 6:30 PM MST.

As far as potential hazards today, thunderstorms have the potential to produce strong gusty winds (DCAPE around 1500 J/kg), small hail, and heavy rain. 

Temperatures today will be relatively mild with high temperatures possibly remaining under 100 degF in Tucson with locations between Phoenix and Yuma remaining between 105 degF and 108 degF.

12z WRF-HRRR 2-meter temps for today at 4:00 PM MST.

Tomorrow's Forecast

The mid level ridge is forecast to continue flattening out and become centered over southern Texas by tomorrow lowering 500mb heights to between 590 and 592 dm across Arizona. The flow is nearly the exact same with mid level winds southwesterly to westerly. 

12z GFS 500mb heights and vorticity for tomorrow at 18z.

The only significant difference in the synoptics is the speed divergence at 300mb that has been aiding convective development will not be present as the jet streak is forecast to be centered over the Southern Plains by tomorrow. 

12z GFS 300mb winds and heights for tomorrow at 18z.

Thermodynamics will be only slightly less favorable tomorrow with the 12z KTUS WRF-HRRR sounding forecasting 1.48 in of pwat and CAPE of 1159 J/kg just prior to forecast convective initiation over the Tucson Mountains. 

12z KTUS WRF-HRRR sounding for tomorrow at 1:00 PM MST.

The 12z WRF-HRRR simulated reflectivity portrays almost an identical scenario to what is forecast for today with storms developing over the Tucson mountains around 1:00 PM MST then impacting the Tucson metro between 2:00 PM MST and 6:00 PM MST. 

12z WRF-HRRR simulated maximum reflectivity for tomorrow at 1:30 PM MST.

12z WRF-HRRR simulated maximum reflectivity for tomorrow at 3:30 PM MST.

12z WRF-HRRR simulated maximum reflectivity for tomorrow at 4:30 PM MST.

12z WRF-HRRR simulated maximum reflectivity for tomorrow at 5:30 PM MST.

Also, with lowering heights and the preexisting low level moisture, temperatures will remain somewhat cooler still with Tucson remaining around 100 degF (or maybe a little less) and temps between Phoenix and Yuma forecast between 105 degF and 108 degF.

12z WRF-HRRR 2-meter temps for tomorrow at 4:00 PM MST.

In general, expect a chance for showers and thunderstorms today and tomorrow afternoon for Tucson and eastward during the afternoon and evening with temperatures much cooler compared to last week.