Forecast Discussion
155 FXUS65 KTWC 191930 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 1230 PM MST Sat Sep 19 2026 .SYNOPSIS...Plenty of sunshine across Southeast Arizona this afternoon with clear skies overnight. A weak disturbance in the lower-to-middle levels of the atmosphere will result in partly cloudy skies Sunday afternoon with even a slight chance for a weak shower. Breezy winds may accompany these light showers. Deeper moisture is then expected to spread back across portions of Southeast Arizona next week for a chance of showers and thunderstorms. High temperatures will be near to slightly above normal into the middle of next week. && .DISCUSSION...The upper pattern today is defined a trough of low pressure across the Intermountain West with a low centered over southern Idaho, a second trough west of this feature aligned along 135W and a strong ridge of high pressure over the SERN U.S. with a high center over east Texas. In the lower-to-middle levels of the atmosphere (850 to 700mb), there is an amplified trough of low pressure over the northern Baja Mexico. The latest GOES precipitable water imagery indicated dry PWATs between 0.50 and 0.65 inches across the majority of Southeast Arizona, with higher values between 0.65 and 0.90 inches NE of Tucson in Graham/Greenlee counties. There is a thin plume of deeper moisture (PWATs 0.80 to 1.00 inches) observed out ahead of the 850-700mb trough axis extending from the Baja Spur into the northern Gulf of California. As we move into Sunday, the Intermountain West trough tracks east into the Northern Plains, bowling over and suppressing the upper ridge across the SERN states. The trough behind it digs southeast, with a low-center finding its way west of San Francisco by 21/00Z Sunday afternoon. This position will force that lower-to-mid level feature over the NRN Baja to eject across SW Arizona tomorrow. Given the weak moisture plume out ahead of it, we may have enough lower-level moisture convergence to support a weak shower to develop across our neck of the woods. I wouldn`t expect anything strong given the shortwave ridging occuring in the middle to upper levels, but since the sub-cloud layer is dry, we may see some gusty/breezy winds to 35 mph accompany the light shower downdrafts. Both of the upper troughs continue to track east, establishing themselves over the Great Lakes and central California by 22/00Z Monday afternoon. Amplified shortwave ridging in between these two features will support the subtropical ridge to build back into the SERN states the first half of next week. The resulting southerly flow across Sonora/Chihuahua MX will draw moisture northward again. Although the bulk of the moisture will advect into New Mexico, we will see a general deepening of moisture across eastern portions of Southeast Arizona, mainly east of Tucson. At this time, the best deformation between the upper trough to our west and the subtropical ridge to our east will set-up across New Mexico. This is supported by the WPC Excessive Rainfall Outlook (ERO) in the slight category across New Mexico (at least 15% risk rainfall will exceed flash flood guidance) both Tuesday and Wednesday. In Southeast Arizona, we should have enough lift/moisture across the eastern half of our CWA to support scattered showers and thunderstorms. Otherwise, it is still possible that we will see some tropical influence the second half of next week into next weekend especially given the strong ridging to our east. However, plenty of uncertainty still on the timing and track of southerly systems and the overall extent of deeper moisture. We will continue the chance of showers and thunderstorms with at least the presence of recycled moisture to aid thunderstorm development. && .AVIATION...Valid thru 21/00Z. SKC conditions from KTUS west today through midday Sunday, then SCT-BKN 8-11k ft AGL with a 5-15% chance for -SHRA. East of KTUS, FEW-SCT clouds at 8k-11k ft AGL this afternoon/evening and again Sunday afternoon. SFC wind less than 12 kts thru the forecast period. Winds favoring a SWLY/WLY direction during the afternoon/early evening hours both today and Sunday...variable in direction at other times. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Dry with plenty of sunshine across Southeast Arizona this afternoon with clear skies overnight. A weak disturbance in the lower-to-middle levels of the atmosphere will imports some moisture into the area resulting partly cloudy skies Sunday afternoon with even a slight chance for a weak shower. Breezy winds may accompany these light showers. Deeper moisture is then expected to spread back across portions of Southeast Arizona next week for a chance of showers and thunderstorms...especially Tuesday through the end of the week. High temperatures will be near to slightly above normal into the middle of next week. Min RH values will be in the 13-20 percent range west of Tucson through the weekend and 20-27 percent in valley locations east of Tucson (25- 40 percent in the mountains). RH values then increase 10-20+ percent east of Tucson next week as deeper moisture moves back into the area. 20-foot winds will be less than 15 mph into at least the middle of next week. Gusty and erratic winds will accompany any thunderstorms. && .TWC WATCHES/WARNINGS/ADVISORIES...None. && $$ Visit us on Facebook, X, YouTube, and at weather.gov/Tucson
NWS TWC Office Area Forecast Discussion