Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
024 FXUS65 KTWC 242037 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 137 PM MST Sat Oct 24 2026 .SYNOPSIS...The combination of a nearby weather disturbance and just enough moisture remaining across the region will result in a slight chance of showers and thunderstorms across southwest Pima county and the northern Tohono O`odham Nation as well as northern Graham and Greenlee counties this afternoon and early this evening. Otherwise, dry conditions are expected areawide through Thursday. Showers are expected to return to the region Friday into next weekend. High temperatures will be below normal this weekend, warming to near to slightly above normal early to mid next week, before lowering back below normal late next week. && .DISCUSSION...The upper pattern this afternoon is defined by an upper-low centered just west of us in western Maricopa county, another upper low off the coast of British Columbia, a neutrally oriented amplified ridge of high pressure off the West Coast and a strong upper-low west of the ridge (centered around 35N/150W) in the Eastern Pacific. The latest GOES precipitable water imagery indicated a modest amount of moisture associated with the upper- low this morning across Arizona, with PWATs 0.60-0.75 inches west of Tucson, and drier air to the east (PWATs between 0.30-0.50 inches). Although the moisture is limited, there should be just enough instability under the upper-low to result in a slight chance of showers, possibly with a thunderstorm across north central Pima and southwest Pinal county this afternoon. In fact, as of 1 PM MST...there are a few weak showers that have developed in extreme southern Maricopa county. Satellite imagery early this afternoon indicated a band of low to mid-level cloud cover that extends from central Pinal county south into the Tohono O`odham Nation along the SW periphery of the upper low. It is possible that this band will result in a slight chance of a weak shower later this afternoon as the upper low drifts east across the Tucson Metro Area, but should really struggle in the drier airmass to produce measurable rainfall. Otherwise, the upper-low to our west eventually ejects northeast Sunday as the upper-low to our NW moves south along the Pacific Northwest coast. The movement of the upper low will be stunted by the upper ridge to it south. The ridge will flatten as this happens, creating a zonal westerly flow across the Eastern Pacific early this week. This is important, because it will allow a deep plume of subtropical moisture to move east under the strong upper low during the upcoming work week. Models still have some uncertainty on the exact strength, timing and track of the upper-low as it shears out into the zonal flow and tracks east into the Desert Southwest, but the general consensus is for showers and thunderstorms to impact Southeast Arizona Friday and Saturday with a stronger trough passage Sunday. The 24/19Z 24-hr pcpn percentiles (25th/50th/75th) for for KTUS are: Percentile of 24-hr PCPN (inches) Day25th 50th75th Friday 0.12in 0.37in 0.56in Saturday 0.07in 0.36in 0.53in Sunday 0.16in 0.63in 1.21in Monday 0.00in 0.37in 0.50in In any event, it looks like a ramp up in activity the end of the upcoming week into next weekend with heavy rainfall possible Sunday. && .AVIATION... Valid through 26/00Z. SCT-BKN clouds at 6k-9k ft AGL thru 25/03Z with a slight chance of weak -SHRA/-TSRA...then clearing overnight. SFC wind SW 12-16 kts with gusts to 25 kts east and southeast of Tucson in the vicinity of KALK and KDUG through 25/03Z, then SFC wind less than 12 kts and terrain driven other times. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...The combination of a nearby weather disturbance and just enough moisture remaining across the region will result in a slight chance of showers and thunderstorms across southwest Pima county and the northern Tohono O`odham Nation as well as northern Graham and Greenlee counties this afternoon and early this evening. Otherwise, dry conditions are expected areawide through Thursday. Showers are expected to return to the region Friday into next weekend. High temperatures will be below normal this weekend, warming to near to slightly above normal early to mid next week, before lowering back below normal late next week. 20-foot winds will generally be 15 mph of less through at least the middle of next week. Minimum RH values will be in the 25-40 percent range in the valleys through Sunday (higher in the mountains), in the 18-30 percent range Monday and lowering into the 15-25 percent range Tuesday and Wednesday. && .TWC WATCHES/WARNINGS/ADVISORIES...None. && $$ Visit us on Facebook, X, YouTube, and at weather.gov/Tucson