Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
598 FXUS65 KTWC 221621 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 921 AM MST Wed Jul 22 2026 .SYNOPSIS... Expect a downturn in thunderstorm activity across Southeast Arizona today with widely scattered showers and thunderstorms mainly east of Tucson today. Although we will maintain a low-grade thunderstorm pattern the next few days, we will also see afternoon high temperatures rapidly increase late this week into this weekend. The upper pattern eventually moves into a more favorable location for an increased potential for strong and organized thunderstorms Saturday and Sunday. && .UPDATE... Forecast is on track for a downward trend in thunderstorm activity this afternoon and evening. Lingering moisture will allow for thunderstorms and cloud build-ups in the mountains thanks to orographic lift, but will struggle to maintain structure and/or come off the terrain into the valleys. Best chances for storm development is in the White Mountains at 30-60% chance then the rest of the Sky Islands at 30-50% chance. With these storms, there can be locally heavy rainfall and gusty outflows. && .PREV DISCUSSION... The theme of today`s forecast is best summed up by the Greek philosopher Heraclitus who was attributed as saying, "nothing endures but change." I think this fits because we will see several changes over the next several days across Southeast Arizona. First, we are finally shifting away from the wet period we have been in the past several days where widespread showers and thunderstorms produced significant rainfall to the east and south of Tucson. Expect a significant downturn in thunderstorm activity today as we are finally in the subsident wake of the upper disturbance which is currently observed on GOES water vapor imagery moving north through NE Arizona. In addition, the GOES precipitable water imagery indicated a drier airmass (between 1.10 and 1.25 inches of PWAT) in central Chihuahua Mexico that will move NNW into the eastern portions of the CWA both today and tomorrow...eroding the deep moisture that has been in place. The 22/00Z CAMs are all over the place with both the timing and track of an MCV that is seen over extreme NW Chihuahua early this morning. My hunch tells me we will see this feature hover along the AZ/NM border as it moves north through the mid-morning morning hours and this too will result in a subsident wake as well. What does this all mean, I would expect a low-grade Monsoon day with widely scattered showers and thunderstorms east of Tucson working off of the residual moisture. The big change with the forecast will occur the next few days as the strong upper-high center over Oklahoma moves WSW into SRN New Mexico by 24/00Z Thursday afternoon then into ERN Arizona by 25/00Z Friday afternoon. We will see afternoon temperatures jump rapidly from a few degrees below normal today to 6-10 degrees above normal both Friday and Saturday. The 22/00Z NBM temperatures for the Tucson International Airport (KTUS) seem a little too low with the MaxT of 106 degrees. The NBM probability of 110+ degrees for KTUS is currently at 2-5% for both Friday and Saturday. This contrasts with the deterministic 22/00Z GFS and ECMWF 850-700mb thicknesses that both suggest a thickness between 1700-1710 m which translates via regression equation to to a MaxT of 110-114. Even the old-school MEX MOS guidance even has 111/112 FRI/SAT. I do think that given the saturated soil moisture across Southeast Arizona right now, that we can shave off a few degrees from this...but it may still be hot enough to elevate the HeatRisk across Southeast Arizona. Given the uncertainty at this time, I will punt the decision on any extreme heat products to the dayshift. Otherwise, the heat is not the only change. The upper-high moves into a more favorable location near the Four Corners Saturday then NW Arizona Sunday. This opens our neck of the woods up to a rim-shot pattern. The combination of strong surface heating, drier air aloft and modest mid-level flow will increase the potential for stronger, more organized clustering of showers and thunderstorms next weekend...especially Saturday. With the change, the Monsoon rolls-on. && .AVIATION... Valid through 23/18Z. SCT-BKN 12-15k ft AGL through 22/20Z this afternoon, then SCT- BKN 6-8k ft AGL and BKN 12-14k ft AGL with widely scattered -SHRA/-TSRA generally to the east of KTUS. VFR, with the exception of brief MVFR due to stronger showers and thunderstorms...especially near KDUG. Surface winds generally less than 12 kts, except for around storms where VRB gusts to 35 kts will be possible. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER... Expect a downturn in thunderstorm activity across Southeast Arizona today with widely scattered showers and thunderstorms mainly east of Tucson today. Although we will maintain a low-grade thunderstorm pattern the next few days, we will also see afternoon high temperatures rapidly increase late this week into this weekend. The upper pattern eventually moves into a more favorable location for an increased potential for strong and organized thunderstorms Saturday and Sunday. Min RHs 25-30% in the lower desert locations and above 40% in the mountains today. By Thursday into the weekend, RHs could dip into the 17-22% range for the lower deserts west of Tucson and the upper Gila River Valley as temperatures warm to above average. Winds this week will remain mainly light and under 15 mph, though strong and erratic winds will be possible with any thunderstorm. && .TWC WATCHES/WARNINGS/ADVISORIES... None. && $$ Update...JT Visit us on Facebook, X, YouTube, and at weather.gov/Tucson