Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
676 FXUS65 KTWC 212036 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 136 PM MST Mon Sep 21 2026 .SYNOPSIS... A modest increase in moisture will bring partly cloudy skies with a slight chance of a shower this afternoon and early this evening. Moisture will continue to increase after today bringing daily chances for showers and thunderstorms through much of the week. && .DISCUSSION... An upper low over central-southern California will continue to bring southwesterly flow across the region. Tucson`s PWATs are currently 0.89 inches from GOES and moisture content will increase through the rest of the day. Majority of the moisture will be in the form of cloud but there are slight chances for shower and thunderstorms from Tucson and east. The upper level low over central-southern California will continue to bring moisture for the next 3 days. The bulk of the moisture will be sitting to our east and Tucson will be on the outer edge of above normal moisture. There will be daily chances for rain showers and thunderstorms through Thursday. Latest CAM guidance has showers starting late tonight and increasing coverage by tomorrow afternoon. There are 10% from Sells to 50% by the New Mexico state line for a quarter of inch of rain in a 6 hour period. Chances for half inch are 10-40% in a 6 hour period will be along the state line. Rain and thunderstorm chances will continue through Thursday. By Friday, upper level moisture will decrease and as result, lower chances for rain showers and thunderstorms. Daily chances will return by Sunday, but there are still disagreement on how the ensembles try to resolve the influence of Tropical Storm Polo. For now, rain and thunderstorm chances will be 25-30% for the start of the new week. && .AVIATION...valid through 23/00Z. SCT-BKN high clouds at 20-25K ft AGL through the forecast period. SCT-BKN 8k-11k ft ceilings developing through the rest of the afternoon and into tomorrow. A 10-15 percent chance of a -SHRA/-TSRA this afternoon from KTUS and east. Chances increase through the night for SHRA through the night followed by -TSRA chances by tomorrow mid-morning to early afternoon. Surface winds will be less than 12 kts through the forecast period. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER... Minimum relative humidity 20-30 percent in the lower elevations and 30-40 percent in the mountains today, increasing further for the remainder of the week especially across Graham, Greenlee, and Cochise counties. Chances for showers and thunderstorms will also arrive daily Tuesday onwards with this moisture increase. Gusty and erratic winds will accompany any thunderstorms. && .TWC WATCHES/WARNINGS/ADVISORIES... None. && $$ Visit us on Facebook, X, YouTube, and at weather.gov/Tucson