Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
573 FXUS65 KTWC 211037 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 337 AM MST Mon Sep 21 2026 .SYNOPSIS... A modest increase in moisture will bring partly cloudy skies with a slight chance of a weak shower this afternoon and early this evening. Moisture will continue to increase after today bringing daily chances for showers and thunderstorms through much of the week. && .DISCUSSION... Today, an upper low will move into central-southern California while a downstream shortwave ridge exits southeastern Arizona to give way to southwesterly flow. Satellite derived moisture values aren`t terribly impressive this morning with precipitable water at 0.8-1 inches, however with the trough nearby a slight chance of a shower or thunderstorm is in the forecast this afternoon mainly east of central Pinal/Pima through the New Mexico border. Moisture is expected to advect north out of Mexico tonight as low-mid level flow turns southerly, which will keep a slight chance of a shower in the forecast through the night. Tuesday through Thursday will see upper level troughing persist over southern California and northern Baja, while a southerly stream of moisture continues, mainly focused over New Mexico with central Pima on the western periphery. Precipitable water should increase to 1-1.25 inches in this area and combined with persistent upper level support, shower/thunderstorm chances will increase to 30-60 percent in eastern areas of the state.. Precipitation chances lower a bit Friday into the weekend as the upper level wave finally exits the region. Confidence in any one forecast solution in this period going forward deteriorates as ensemble models disagree on the flow pattern as well as the potential influence of Tropical Storm Polo currently off the southwestern Mexico coast. At this moment the forecast favors just low end rain chances through early next week with most ensemble members keeping tropical activity away from the region through mid-week next week. && .AVIATION...Valid through 22/12Z. Mainly SKC through the morning. SCT-BKN 8k-11k ft ceilings after 21/18Z with 10-20 percent chance of a -SHRA/-TSRA. Slight chance of -SHRA through the night but with lower confidence. Surface wind west/southwest 6-11 kts this afternoon and early evening, otherwise light and terrain driven. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER... Minimum relative humidity 20-30 percent in the lower elevations and 30-40 percent in the mountains today, increasing further for the remainder of the week especially across Graham, Greenlee, and Cochise counties. Chances for showers and thunderstorms will also arrive daily Tuesday onwards with this moisture increase. Gusty and erratic winds will accompany any thunderstorms. && .TWC WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Edwards AVIATION...Edwards FIRE WEATHER...Edwards Visit us on Facebook, X, YouTube, and at weather.gov/Tucson