Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
387 FXUS65 KTWC 192113 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 213 PM MST Tue Aug 19 2025 .SYNOPSIS...Isolated to scattered thunderstorms this week across Southeast Arizona, with day to day variability in intensity and chances. The big story for Southeast Arizona will be the extreme heat returning the second half of the week. An Extreme Heat Warning is in effect Wednesday morning through Friday evening. && .KEY MESSAGES... - Main story will be the increase in temperatures through the week and into the weekend, especially the abnormally warm low temperatures, resulting in areas of Major HeatRisk. - Extreme Heat Warning in effect 10 AM Wednesday to 8 PM Friday for much of the lower desert areas in southeast AZ, including Pinal and Pima counties, the Upper Gila River Valley and the Upper San Pedro River Vally. - Daily thunderstorm chances through the upcoming week, mainly bringing Minor Risk of strong, gusty winds and localized flash flooding with any strong thunderstorms. && .DISCUSSION... The 4 corners high is here (finally) and looks to stick around for a bit bringing daily chances for showers and thunderstorms across Southeastern Arizona. Afternoon thunderstorms have begun to tower and form, mainly in the higher terrain of the Sky Islands east of Tucson. This will be the norm as storms will struggle a tad to come off the mountains this afternoon and evening. The 18Z sounding this afternoon shows the main threat is flash flooding with the relatively slower storm motion at 5 to 10 kts and the PW coming in at 1.54 inches approaching the 90th percentile of PW when compered to climatology. Compared to this time yesterday, today`s 18Z sounding shows less dry air above the 500 mb pressure line, allowing for the potential for taller storms to form compared to days past but still lacks in instability and CAPE. Strong outflow winds of 30-40 mph are still possible with any storm. The best chances for thunderstorm activity remain east of Tucson this afternoon and evening. Tucson is on the outer fringes of the best chances, with the most likely scenarios for storms in the metro would be from storms coming off the higher terrain in the Catalinas and Rincons or getting some thunderstorms moving from the Vail and Corona de Tucson areas to the NE. Outside of today, daily showers and thunderstorm chances continue with greater coverage of PoPs tomorrow expanding westward giving slight chances into Western Pima County and Tohono Nation Wednesday onward. The temperatures continue to rise 4 to 6 degrees above normal with warmer overnight lows bringing Major HeatRisk into the area Wednesday through Friday, thus the Extreme Heat Warning remains in place. As previous discussions mentioned, the high pressure begins to drift southward early to mid next week, allowing for the potential for more moisture to be shunted into the area, however this all depends on how fast the ridge can break down and the low pressure over the Pacific will influence the ridge. && .AVIATION...Valid through 21/00Z. SCT-BKN clouds AOA 10-15K with isolated -SHRA/-TSRA from KTUS eastward now thru 20/06Z and again aft 20/19Z thru the end of the period. Light and terrain driven winds through the forecast period with gusts up to 40 kts possible with any thunderstorm today. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Expect daily chances for thunderstorms and wetting rain showers into next week. Min RHs will generally be 15-20 percent in the lower elevations and 20-30 in the mountains. Winds will generally be less than 15 mph with typical afternoon gusts up to 20 mph into next week. Temperatures will be above normal this week, with an Extreme Heat Warning in the lower elevations of Southeast Arizona Wednesday through Friday. && .TWC WATCHES/WARNINGS/ADVISORIES... Extreme Heat Warning from 10 AM Wednesday to 8 PM MST Friday for AZZ501>507-509. && $$ Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson