August 4th: Hot and Dry through Sunday, Slight Uptick in Moisture Possible Early Next Week

 Synopsis

The mid level anticyclone will remain centered between southwestern New Mexico and southeastern Arizona today through this weekend leading to hot and abnormally dry conditions for this time of year. Daytime temperatures are likely to reach excessive heat criteria (temps >= 110 degF) across the lower deserts Friday through Sunday. Models are hinting at an increase in moisture sometime early next week which could possibly lead to slightly cooler temps and an uptick in convection. 


Current Conditions

SPC 500mb analysis this morning displays the mid level ridge centered over Southwest New Mexico at 594 dm. 


SPC 500mb analysis at 17:00Z this morning.

Over the past few days our atmosphere has dried out significantly with pwats plummeting from 1.25 in yesterday at 12Z down to 0.79 in this morning as shown in the 12Z TUS sounding from this morning below.


12Z TUS Sounding courtesy of the SPC.

For perspective on how dry it is, 0.79 in of precipitable water in Tucson is down to the 10th percentile based on sounding climatology for this time of year. 


TUS sounding climatology for total precipitable water courtesy of SPC.



Today through Sunday

A shortwave trough moving through Northern California this weekend will prevent the ridge from building northward and remain centered near southwestern New Mexico and southeastern Arizona. The ridge is expected to strengthen through the weekend with 500mb heights increasing to 598 dm over southern Arizona by Sunday leading to hot, dry conditions across our region through at least Monday. 

12Z GFS 500mb heights and vorticity for tomorrow at 12Z.

12Z GFS 500mb heights and vorticity for Sunday at 18Z.


Considering the very dry and stable air mass overhead today through the weekend, convection will remain suppressed with only a few shallow cumulus developing over the highest mountain peaks. The main focus will be excessive heat with high temperatures reaching over 110 degF across the lower deserts starting today and most likely persisting into early next week. 

12Z WRF-HRRR 2-meter temps for today at 5:00 PM MST.


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


12Z WRF-HRRR 2-meter temps for Sunday at 4:00 PM MST.


Next Week

Over the past 24 hours the GFS and ECMWF as well as their ensemble members are in better agreement with regards to the positioning of the mid level ridge early next week. Models forecast the ridge to weaken slightly becoming centered farther south and east near the International Border in far western Texas by Tuesday. 

12Z GFS 500mb heights and vorticity for Tuesday at 18Z.


This pattern could open the door for some moisture to be advected from the south as well as lower daytime temperatures by a couple degrees. At the same time, a tropical cyclone is likely to develop in the Eastern Pacific a few hundred miles off the coast of west-central Mexico over this weekend. The National Hurricane Center has a 80% chance of development over the next 2 days.

National Hurricane Center Two-Day Tropical Outlook.

Models forecast this tropical cyclone to move west-northwest over the next few days and pass by the tip of the Baja Peninsula on Tuesday. Models also are hinting at the potential for this feature to induce a significant Gulf of California moisture surge which could significantly increase precipitable water and possibly thunderstorm activity across southern Arizona. Will need to monitor this closely over the next couple of days as slight variations in the positioning of the 500 mb ridge and the track of this developing tropical cyclone could significantly impact the amount of moisture transported into our region. 


For now, expect an increase in moisture, slightly cooler temperatures, and the potential for an uptick in thunderstorm activity across our region early next week. Stay tuned! 


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