July 25th, 2024: Rinse and Repeat Today

Synopsis

 The 500mb anticyclone will remain anchored over the Lower Colorado River Valley with northeasterly/northerly flow aloft over Arizona today. Moisture is primarily dependent on the Gulf of California, but should remain sufficient for showers and storms across mainly the eastern half of the state this afternoon and evening. Near identical pattern today as compared to yesterday, so strong with even a few severe thunderstorms are possible in Phoenix and Tucson again with main threat being severe grade wind gusts. 




Yesterday's Cliff Notes


A few storms fired up in Phoenix last night producing quite the bolt show across the metro. The storms were relatively short-lived, but had some attitude as SPC Storm Reports had a few areas around the metro with damage to trees, buildings, and solar panels. Rain amounts were highly variable with Sky Harbor reporting a trace and highest values over 0.50 inch where thunderstorm microbursts occurred. Was keeping an eye on a couple outflow boundaries diving down from the northeast and northwest into the Phoenix metro, but those did not initiate the storms by themselves. Those outflow boundaries collided with an outflow boundary moving in from the southwest from a strong storm cluster in eastern Pinal County. Definitely the most active evening in Phoenix this season thus far.


In Tucson, cells initiated to the north and west of the city throughout the afternoon with only one rogue storm moved through the metro in the middle of the afternoon. Other than that, it was disappointing in Tucson with minimal storm coverage and precipitation amounts.



Current Conditions


The synoptic pattern is nearly unchanged today with the 500mb anticyclone centered over the Lower Colorado River Valley and northerly/northeasterly flow aloft over Arizona.


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


The cutoff low off the coast of CA and the trough in the Pacific Northwest will influence the synoptic pattern tomorrow into the weekend.


Moisture has increased especially in southeast Arizona as indicated by the 12z TUS sounding which shows 1.51 inches of precipitable water compared to the 1.21 inches from 12z yesterday.


12z TUS sounding courtesy of the SPC.

The thermodynamics look much better today compared to yesterday with deeper low level moisture, a weaker mid level subsidence inversion, and increased buoyancy. 




Today's Forecast


Synoptics


As mentioned above, almost a rinse and repeat synoptic pattern with the 500mb anticyclone anchored over the Lower Colorado River Valley. The only difference today is mid level northerly/northeasterly flow will be a bit weaker. Other than that, the lack of any synoptic scale forcing mechanism (i.e. shortwave trough) means storms will once again be thermodynamically driven and dependent on outflow boundary trajectories and efficiency.



Thermodynamics


Plenty of moisture to work with today as CAMs forecast between 1.25 and 1.75 inches of precipitable water and 2-meter dew points in the 50s to low 60s (moisture increasing from east to west) throughout the day today.


12z WRF-HRRR precipitable water valid for 5:00PM MST this afternoon.




12z WRF-HRRR 2-meter dew points valid for 5:00PM MST this afternoon.

Model soundings for Tucson and Phoenix forecasting sufficient buoyancy this afternoon and early evening with between 500 and 1000 J/kg of Mixed Layer CAPE as sufficient surface heating will allow low to mid level lapse rates to steepen throughout the day.


12z KTUS WRF-HRRR sounding valid for 5:00PM MST this afternoon.



12z KPHX WRF-HRRR sounding valid for 5:00PM MST this afternoon.


Expecting higher values of CAPE in Phoenix again this afternoon and evening due to higher surface temps and low level moisture. DCAPE forecast to once again be around 1500 J/kg highlighting the threat for strong to severe wind gusts. The vertical wind profile is a bit more favorable in SE AZ today (as shown in the KTUS sounding above), so that could favor better organization of storm clusters coming off the higher terrain. 

Other than that, thermodynamics are very similar to yesterday.



What to Expect/Impacts


Overall, expecting a similar outcome today as synoptic and thermodynamic conditions are near identical compared to yesterday. CAMs are in good agreement storms will initiate over the Mogollon Rim and White Mountains early this afternoon.


12z WRF-HRRR simulated reflectivity for this afternoon at 2:00PM MST.


Outflow boundaries are forecast to move southward/southwestward into the lower deserts throughout the late afternoon and early evening time frame.


12z WRF-HRRR simulated reflectivity for this afternoon at 5:00PM MST.


12z WRF-HRRR simulated reflectivity for this evening at 7:00PM MST.


12z WRF-HRRR simulated reflectivity for this evening at 9:00PM MST.


There are some differences among CAM solutions regarding the timing and coverage of storms in the lower deserts which is to be expected. Thermodynamics will be sufficient, but storm development will be primarily dependent on outflow boundary trajectories and efficiency to induce ascent. 


SPC has Southern Arizona (including Tucson and Phoenix) in a marginal risk of severe storms with the primary threat being severe grade wind gusts (5%). The 12z HREF highlights this potential which shows a 70% probability of 4-hour max wind speeds in excess of 30 knots (were dbz > 20) in Southern and South-Central AZ this evening.


12z HREF 4-hour max wind speeds and probability of wind speeds in excess of 30 knots where dbz > 20 valid for 7:00PM MST this evening courtesy of SPC.


Some locations could see wind gusts in excess of 60 mph. With that being considered, traveling conditions will be extremely hazardous this evening along the I10 corridor between Tucson and Phoenix as well as along the I8 corridor between Casa Grande and Gila Bend. Could even see some strong wind gusts into Yuma County as well. Main hazard is blowing dust causing reduced visibility.


Excessive rainfall is unlikely, but isolated flash flooding is possible especially within or near microbursts.



Tomorrow's Forecast


The aforementioned closed low off the CA coast will become embedded in the westerlies and move into Northern California tomorrow. This will cause the 500mb ridge to flatten and displace the mid level anticyclone farther south into Mexico.


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


Mid level flow becomes quite messy across AZ, but still somewhat northerly/northeasterly.


CAMs forecast a bit of drying tomorrow, but sufficient moisture remains in place with pwats forecast to be between 1.25 and 1.50 inches tomorrow afternoon.


12z WRF-HRRR total precipitable water for tomorrow afternoon at 5:00PM MST.


Instability tomorrow could be impacted by this evening's convection, so will hold off on providing additional details. In general, expect another active day tomorrow with storm coverage and intensity dependent on low level moisture and if the atmosphere is overworked from today's activity. 






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