July 4th, 2024: Hot and Dry Fourth of July

 Synopsis

A high amplitude mid level ridge over the West Coast of CONUS will provide dry and stable northeasterly flow aloft over AZ today through the weekend. This pattern is expected to suppress convection throughout most of AZ with only a few isolated showers/storms possible near the International Border in extreme SE AZ. With a dry and stable atmosphere, high temperatures in the lower deserts are expected to reach excessive heat criteria today and especially tomorrow.


Current Conditions

12z GFS 500mb analysis this morning displays a 594 dm anticyclone centered off the coast of Northern California and dry northerly/northeasterly flow over AZ.


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


This hostile synoptic pattern is evident in the 12z TUS and PHX soundings this morning showing a strong subsidence inversion around 500mb.


12z TUS sounding this morning courtesy of SPC.


12z PHX sounding this morning courtesy of SPC.


Even with hostile mid and upper levels, there is quite a bit of moisture near the surface with dew points in the low to mid 60s across the lower deserts this morning.


Surface observations as of 10:00AM MST courtesy of the NWS.


This low level moisture is from a Gulf of CA surge last night induced by a decaying MCS in Sonora. 



Fourth of July Forecast


The mid level anticyclone will remain centered off the coast of Northern California today with dry northeasterly flow aloft over AZ. Throughout the day, precipitable water values will plummet across the state with CAMs showing pwats dropping to an inch or less by late this afternoon.


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


Rapid drying and subsidence (indicated by the 12z WRF-HRRR KTUS sounding) will eliminate any chances for storms across much of the state.


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


Can't rule out a couple isolated cells near the International Border in Cochise County due to just enough moisture and instability expected to remain in that area throughout the afternoon.


Otherwise, expect a sunny and hot Fourth of July across AZ with high temps between 100 and 105 degF in the lower deserts of SE AZ (including Tucson) and between 110 and 115 degF in the lower deserts between Phoenix and Yuma.


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


CAMs forecast another Gulf Surge overnight tonight with 2-meter dew points forecast to increase into the upper 50s to mid 60s in the lower deserts.


12z WRF-HRRR 2-meter dew points for tomorrow morning at 2:00AM MST.


This seems likely as CAMs are forecasting another active evening in Sonora tonight. With dew points expected to increase tonight, this will make it difficult for temps to cool likely keeping temps in the mid to upper 80s overnight.



Tomorrow


The mid level anticyclone is forecast to reach peak amplitude tomorrow afternoon and become centered near the California/Oregon Border. 


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


Arizona will remain under a dry northeasterly flow aloft with precipitable water expected to remain below an inch.


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


High temperatures are expected to be extremely hot tomorrow with temps between 105 and 110 degF in the lower deserts of SE AZ  (including Tucson) and between 110 degF and 115 degF in the lower deserts between Phoenix and Yuma.

12z WRF-HRRR 2-meter temps for tomorrow at 3:00PM MST.

Some isolated areas in Maricopa and Yuma County could see temps reach 117 or 118 late tomorrow afternoon. 


Regarding any storm chances, both the 12z and 15z WRF-HRRR are forecasting a few elevated showers and thunderstorms across extreme SE AZ tomorrow afternoon. 


12z (left) and 15z (right) WRF-HRRR simulated reflectivity for tomorrow afternoon at 4:00PM MST.




The 12z KTUS WRF-HRRR sounding forecasting an inverted-V sounding with near dry adiabatic lapse rates from the surface to 500mb, a shallow layer of CAPE in the mid levels, and surface temps reaching the convective temperature tomorrow afternoon.


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



Even with a tad bit of CAPE, a moisture starved atmosphere and a strong subsidence inversion above 500mb would make it very difficult for any storm to develop. Will need to monitor this afternoon and tomorrow morning CAM runs to see if this scenario is consistently being forecast. Otherwise, expect a very hot and dry day tomorrow.





 





 


 

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