Forecast Discussion
620 FXUS65 KTWC 230954 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 254 AM MST Tue Sep 23 2025 .SYNOPSIS...Above normal moisture across the region will result in isolated to scattered rain showers and thunderstorms today and less so tomorrow. A weather system will bring stronger storms starting Thursday with impacts gusty winds and risks for flash flooding. && .KEY MESSAGES... Today and tomorrow: Isolated thunderstorms and rain showers for areas south and southeast of Tucson. Less chances and coverage on Wednesday. Temperatures will be running 3-6 degrees above seasonal normal. Thursday-Weekend: A weather system will bring stronger thunderstorms and high chances for wetting rain showers. - Increasing risk for flash flooding starting Thursday for areas east of Tucson, and expanding westward by Friday, and lasting into weekend. - Expect strong gusty and erratic winds from thunderstorms. && .DISCUSSION...Water vapor imagery has a low pressure center located west of the San Diego with a minor ridge over Southeast separating another low pressure center in Colorado. The minor ridge will keep Southeast Arizona`s temperatures elevated by 3-6 degrees today and through at least Thursday. The upper level dynamics are not conducive for thunderstorm organization today, but we do have above normal moisture sitting right on top of us. We will have to rely on the classic heating to any storm or shower development. The favorite areas will be in Santa Cruz and Cochise Counties and along the International Border. Tomorrow, there will less chances and the mountains will be on the receiving end of the rain showers. The big weather story will be hinging on our main player, the San Diego low pressure center. This system will start to move inland to continue bringing above normal monsoon moisture and also tapping into some upper level dry air. This points to a good signal for thunderstorms so far. The real star of the show will be the diffluence field that will be over Southeast Arizona starting on Thursday. Diffluence aloft will bring two main impacts for the region. 1. This environment will support strong to severe thunderstorms, leading to gusty erratic winds and hail. EFI shows 88% confidence for CAPE and shear values above climate norms. CAPE values will generally be 1,000-1,600 J/kg with shear at least 15 kts and possibly up to 25 kts on Thursday and Friday. Plus, medium range convective forecasts guidance has 15-30% signal for strong storms. Active day indeed. 2. We will be sitting at 120-150% above normal precipitable water by the end of the week. Ensemble cluster analysis highlights Friday as one of the wettest days of the week with rainfall amounts at least 0.25" for widespread to areas getting up to an inch for a single day. The south-southwest flow will enhance more rainfall amounts closer to an inch on the mountains and windward facing sides. Therefore, there will be increasing risk for flash flooding starting Thursday for Cochise, Graham, and Greenlee Counties. The risk spreads westward into Pima, Santa Cruz, and Pinal Counties on Friday and possibly lasting into Saturday and Sunday. Ensemble models show the weather system lingering around this weekend, leading to more chances for rainfall and thunderstorms. Flash flooding risk will be still elevated, depending on how the weather system exits. More will tell in the coming days, but for now, expect a very active weather pattern Thursday through the weekend. Be storm ready! On other news, temperature will be down to slightly to near normal by the weekend. && .AVIATION...Valid through 24/12Z. SKC this morning then becoming FEW-SCT 8-12k ft AGL by 23/18Z. Isolated TSRA/SHRA after 23/19Z through 24/02Z, mainly south and southeast of KTUS. Gusty and erratic winds to around 35 kts will accompany thunderstorms. Outside of thunderstorms, SFC winds will light and variable in the morning and again in the overnight hours. This afternoon, northwest winds less than 12 kts. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Above normal monsoonal moisture will linger today and tomorrow, providing isolated thunderstorms and rain showers south and east of Tucson. Min relative humidities will be bottoming out at 20-30 percent today through Thursday. By Thursday, a weather system will bring higher chances for wetting rain showers and stronger thunderstorms through the start of the weekend. Outside of thunderstorm winds, general winds will be less than 15 mph with the occasional gust up to 20 mph today and tomorrow. The Gila Valley will have southeasterly breezes in the early Thursday morning. Expect southerly to southwesterly breezes late Thursday through Friday due to the incoming weather system. Daytime temperatures will be running 3-6 degrees above normal through at least Thursday and dropping to near normal by the weekend. && .TWC WATCHES/WARNINGS/ADVISORIES... None. && $$ Strongman Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson
NWS TWC Office Area Forecast Discussion