Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
864 FXUS65 KTWC 221034 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 334 AM MST Tue Sep 22 2026 .SYNOPSIS... Increasing chances for showers and thunderstorms today across much of southeastern Arizona, especially near and east of Tucson and Nogales. Stronger thunderstorms today may produce heavy rain and an isolated threat of flash flooding. Chances continue over the next several days with lowering chances Friday and Saturday. && .DISCUSSION... In the mid to upper levels, a trough sits over southern California and northern Baja today, while southerly flow in the lower levels will draw moisture northward into the desert southwest. By this afternoon precipitable water values will have risen to 1.2-1.45 inches from central Pima eastward while surface dew points will be mainly in the 50s. Early morning satellite imagery shows an expansive moving into the region out of northern Sonora and Chihuahua, which may keep instability on the low end today depending on its coverage over southeastern Arizona. Rain chances of 30-70 percent are fairly widespread today from central Pima through the New Mexico border as the nearby trough will kick off showers and thunderstorms mainly this afternoon and evening. If there is a threat for heavy rainfall rates and potentially flash flooding, it will likely need to come from areas that see some sun and surface heating today to drive stronger thunderstorm chances. The 00Z HREF shows a potential for heavy rainfall rates on the western end this cirrus shield from Santa Cruz and western Cochise counties into the Tucson metro, though again this will be highly dependent on adequate insolation. Otherwise further east longer durations of moderate rainfall rates may also produce flooding concerns, but this threat will likely need multiple rounds of storms cells passing over a specific area. On the river flooding side, the Gila River will need to be monitored out of New Mexico with the heavy rainfall potential out east today. Scattered rain showers may continue through the night, especially through Cochise, Graham, and Greenlee counties, as a shortwave impulse will kick out of the parent trough late tonight through Wednesday. Shower and thunderstorm chances continue on Wednesday with the lingering upper level support, though timing is still uncertain if early morning activity lasts longer into the day additional development may be limited. Thursday comes with the same story as the main trough should begin to move through and eventually exit the area, but with uncertain instability and precipitation coverage. Chances are mainly kept to areas near the New Mexico border on Friday with the trough`s exit and Saturday has a mainly dry forecast. Low end chances return Sunday into early next week as a shortwave trough should cross to the north. Differences in timing and trough amplitude keep these chances in the 10-30 percent range each day for now. The eastern Pacific remains active this week with Polo now a hurricane off the southwest Mexico coast. Polo is forecast to remain well to the south into the weekend, with uncertainty in its path or even approach towards the southwest United States beyond that. && .AVIATION...Valid through 23/12Z. Increasing coverage of 9k-11k ceilings, mainly near and east of KTUS-KOLS today, with FEW-SCT down to 6k after 22/18Z. Isolated -SHRA/-TSRA possible this through 22/18Z then scattered SHRA/TSRA this afternoon and evening, mainly near and east/northeast of KTUS- KOLS. 30-40 kt winds possible with any thunderstorm as well as heavily reduced visibilities. Outside of thunderstorms south/southeast winds this afternoon and tonight of 7-12 kts. Scattered showers should linger through the night in areas east of KTUS. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER... Moisture will increase across much of the region this week along with chances for showers and thunderstorms. Minimum relative humidities today above 30 percent east of Sells and 15-25 percent in western Pima. Minimum relative humidity increases further on Wednesday. Scattered showers and thunderstorms today through Thursday mainly east of central Pima county with isolated chances in western Pima Wednesday night and Thursday. Greatest chances each day closer to the New Mexico border. Winds this afternoon and tonight mainly south/southeast 8-13 mph, with gusty and erratic winds possible with any thunderstorm. && .TWC WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Edwards AVIATION...Edwards FIRE WEATHER...Edwards Visit us on Facebook, X, YouTube, and at weather.gov/Tucson