Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
172 FXUS65 KTWC 041614 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 914 AM MST Fri Sep 4 2026 .SYNOPSIS... Expect scattered thunderstorms each afternoon and evening through the weekend as tropical moisture moves in. The main threat will be heavy rainfall leading to areas of flash flooding. High temperature will will fluctuate between normal and a few degrees below normal. && .UPDATE...Clear skies this morning west of Tucson with generally partly cloudy skies east of Tucson. Plenty of lower level moisture out there with surface dewpoints in the 60s for all valley locations and PWATs ranging from 1.1 inches out west to around 1.5 inches near the NM border. The drier air aloft will preclude convection over the western deserts today, but enough moisture and instability for scattered showers and thunderstorms mainly from the Tucson area eastward. In fact, we`re starting to see some cumulus build-ups on the latest visible satellite imagery with storms getting an earlier start today. 12Z HREF/REFS focusing a bit more on western Graham/western Cochise Counties for a bit more clustering/coverage. With that said, given lack of good forcing aloft for storms, they will mostly be dependent on surface heating. Main concern is that storms will be efficient rain producers with the stronger storms dropping over 1 inch per hour resulting in isolated flash flooding potential. No flood watch headlines planned today given the thinking that flash flooding threat stays more on the isolated side. Otherwise, gusty winds of 30 to 40 mph possible with the stronger storms. See previous discussion below for additional information. && .DISCUSSION... Currently there is lingering clouds with a few showers along the AZ/NM border and south of the international border, with some of the stronger storms having a lightning strike or two. The latest CAMs have little to isolated activity the rest of tonight. Looking into today, the moisture is still in place with a west to east gradient of PWs of 1.0 to 1.7 inches with the highest values Tucson eastward. The upper level pattern has a low pressure system to the NW and Hurricane Marie to the SW of the area and high pressure to the west keeps the South to Southwest flow aloft. This is area is the CAMs are highlighting for activity this afternoon and evening. This lines up with the Slight Risk of flash flooding focusing in on areas east of Tucson. Similar to yesterday, storms will be efficient rainers with accumulations of isolated 1 to 2 inches of rainfall possible with any storm that could lead to flash flooding. Areas that had rainfall today will see quicker responses in creeks, rivers, and washes, especially in Graham, Greenlee, and Cochise counties. As the low pressure system moves to cut off from the main flow and Hurricane Marie moves west, moisture continues to move in, with the bulk of the moisture to the north of the area, however expecting similar PWs similar in current values continue into early next week. This keeps broad slight chances (30-50%) for areas south and east of Tucson. Temperatures will be hovering near normal to slightly below normal through the forecast period. && .AVIATION...Valid through 05/12Z. SCT-BKN clouds 7-12k ft AGL through much of the forecast period, mainly KTUS eastward. Scattered TSRA/SHRA this afternoon and lasting through the overnight period. Although the overnight TSRA/SHRA activity will be more isolated. Near any thunderstorm will have strong gusty winds, heavy rainfall, and brief lowering of ceilings. Outside of thunderstorm winds, winds will be south to southwesterly 5-10 kts from 04/15z thru 05/06z and west to northwesterly aft 05/18z. Light and terrain driven at other times. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER... Expect daily scattered thunderstorms each afternoon and evening today into early next week. There will be some variation in coverage day to day, but expect the bulk of the activity from central Pima County eastward. Heavy rainfall leading to flash flooding will be the main threat. Temperatures will be around normal to a few degrees below normal into early next week. Minimum relative humidity values mainly 20 to 45 percent in the valleys and 30 to 60 percent in the mountains over the next week. Winds will generally remain less than 15 mph and terrain driven through the week. && .TWC WATCHES/WARNINGS/ADVISORIES... None. && $$ Visit us on Facebook, X, YouTube, and at weather.gov/Tucson