Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
733 FXUS65 KTWC 172021 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 121 PM MST Sun Aug 17 2025 .SYNOPSIS....Isolated to scattered thunderstorms today across Southeast Arizona. The main impact with storms in these areas will be the potential for brief, locally heavy rainfall. Otherwise, daily isolated to scattered showers and thunderstorms will persist early in the work week with day to day variability in intensity and chances. Extreme heat will return for the second half of the work with an Extreme Heat Watch issued for Wednesday morning through Friday evening. && .DISCUSSION...A field of cumulus clouds are forming with some towering. Isolated to scattered showers and thunderstorms have started developing focused in Santa Cruz county that will expand into south- central Pima county (southern Tohono O`odham Nation) in the next several hours. Satellite derived PWATs show 1.2 to 1.5 inches and the 18Z KTUS sounding observed 1.46 inches. With substantial moisture still in place the main concern with storms and showers today is brief, locally heavy rainfall. 12Z HREF shows a 30-50% chance for 3 hr QPF greater than 1 inch in Santa Cruz and south- central Pima counties (southern Tohono O`odham Nation) with a 10% chance of greater than 3 inches in Santa Cruz county. High temperatures will be a few degrees warmer than yesterday with Minor to locally Moderate HeatRisk. The high pressure now located over central Texas is still on track to move west by the middle to end of this week. As the high pressure moves to the Four Corners region, there still remains a daily chance for isolated to scattered showers and thunderstorms. Once the high sets up in the Four Corners region by Tuesday, it will intensify increasing temperatures and decreasing moisture here in Arizona. Because of this, an Extreme Heat Watch has been issued for lower elevations in Pima, Pinal, Santa Cruz, Graham and Greenlee counties for Wednesday morning (August 20) until Friday evening (August 22). High temperatures will range from 105 to 110 across much of Pima and southeastern Pinal counties leading to widespread Major HeatRisk with localized Extreme HeatRisk. In other areas of southeastern Arizona, high temperatures will range from 100 to 105 degrees leading to widespread Major HeatRisk. Major HeatRisk is when heat will affect anyone without cooling or hydration and will affect health systems and industries. Additionally, Extreme HeatRisk is rare and long-duration extreme heat with no overnight relief. Once the high pressure begins to weaken and broaden by this coming weekend, temperatures will cool and moisture will return to the area by early next week. More certainty to come as we progress into the work week. && .AVIATION...Valid through 19/00Z. FEW to BKN clouds from KAVQ southward AOA 10k to 13k ft AGL. Clouds will continue to develop becoming more widespread across the area into the early evening hours. Isolated to scattered storms and showers have been developing near KALK and KFHU and will begin developing closer to KOLS aft 17/20Z. Storms and showers will continue until 18/05Z. Expect brief, locally heavy rainfall with these storms and showers. SFC winds will be from the north- northwest at 5 to 10 kts becoming light and variable overnight. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Expect daily chances for thunderstorms and wetting rain showers into early next week. There is a potential for heavy rainfall this afternoon across Santa Cruz and south central Pima county. Min RHs will generally be around 25 to 30 percent in the lower elevations and 45+ percent in the mountains today, generally lowering to 15-20 percent in the lower elevations and 20-30 in the mountains by the middle of next week. Winds will generally be less than 15 mph with typical afternoon gusts up to 20 mph into next week. Temperatures will be around normal through this weekend, trending above normal the second half of next week. && && .TWC WATCHES/WARNINGS/ADVISORIES... Extreme Heat Watch from Wednesday morning through Friday evening for AZZ501>507-509. && $$ Malarkey Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson