Forecast Discussion
046 FXUS65 KTWC 022242 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 342 PM MST Tue Sep 2 2025 .SYNOPSIS...Scattered thunderstorms expected this afternoon mainly from Santa Cruz county through central and western Pima county. A few may develop over the White Mountains as well. Heavy rain with a threat of flash flooding will be the main hazard with any thunderstorm in Santa Cruz and Pima counties today. Additional thunderstorm chances are expected Wednesday. Then Thursday into the weekend precipitation chances will increase as tropical moisture moves into southeastern Arizona. High temperatures will be near normal through Wednesday, then will become below normal the second half of the week. && .DISCUSSION...Scattered showers and thunderstorms have formed over western and central Pima County as of this writing with additional cloud and storm development over the same areas. Training showers and thunderstorms will continue this afternoon and evening across Pima and Santa Cruz counties in an unstable atmosphere with high precipitable water (PW) content. Isolated to widely scattered instances of flash flooding are possible, and the Weather Prediction Center (WPC) has depicted a slight risk (15%) for excessive rainfall which may result in isolated to widely scattered instances of flash flooding. While the primary threat will be focused on heavy rainfall rather than wind, cannot rule out a few locally enhanced outflows (winds gusts around 35-45 mph) resulting in minor blowing dust impacts. Looking ahead to tomorrow, expect similar storm coverage with heavy rainfall being the chief concern again. However, high resolution guidance shows storms first forming a bit more south and east on higher terrain in Santa Cruz county compared to today before pushing gradually west and north. Drier air to the east should limit shower and storm formation to the east along the New Mexico border. Thursday through Saturday richer tropical moisture will move into southern Arizona thanks to Tropical Storm Lorena. The trajectory of Lorena remains rather uncertain. Regardless of the track, even a modest moisture increase could be impactful as the atmosphere will be more conducive to flash flooding. Still keeping an eye on forecast trends to narrow down potential rainfall amounts and associated impacts. && .AVIATION...Valid through 04/00Z. SCT-BKN 9k-12k feet. Scattered TSRA west of KOLS-KTUS-KAVQ through 03/04Z. SFC winds SELY at 9-14 kts becoming WLY to SWLY at KTUS and KOLS after 03/03Z. Gusts up to 40 kts possible near TSRA. Tomorrow, SFC winds SELY to SWLY at 7-12 kts. Scattered thunderstorms again after 03/18Z. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Minimum relative humidity values will be driest in the Gila River Valley this afternoon and Wednesday, then increasing above 25-35 percent the remainder of the week. Humidity will be mainly above 20-30 percent elsewhere this week, especially Thursday through Saturday as a substantial increase in moisture arrives. Southeasterly winds today strongest through the Gila and southeastern Cochise at 13 to 18 mph with gusts to 30 mph. 10-15 mph elsewhere from Tucson to Nogales west. Scattered thunderstorms will continue this afternoon from Santa Cruz through central and western Pima. A few may also develop over the White Mountains. Additional chances again on Wednesday, then increasing chances across southeastern Arizona to end the week as moisture moves in. && .TWC WATCHES/WARNINGS/ADVISORIES...None. && $$ DVS Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson
NWS TWC Office Area Forecast Discussion