Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
838 FXUS65 KTWC 201038 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 338 AM MST Sun Sep 20 2026 .SYNOPSIS... A modest increase in moisture today will bring some afternoon clouds and a very slight chance of a shower. Moisture will further increase this coming week bringing chances for showers and thunderstorms. && .DISCUSSION... The upper levels this morning features mostly westerly flow over southeastern Arizona, while a Pacific low approaches the California coast. Ahead of this low, low amplitude ridging will move over southeastern Arizona today, with a modest increase in precipitable water from the south. This shortwave ridging will suppress overall precipitation chances today, but an isolated shower/thunderstorm can`t be ruled out with the moisture increase. While the initial Pacific low will cross central Canada into the Intermountain West Monday and Tuesday, broad troughing will linger centered over southern California and northern Baja. Upstream of this troughing, moisture will surge northward, especially over New Mexico into eastern Arizona. Daily shower and thunderstorm chances increase to the 30-50 percent range from Tuesday through much of the week across Graham, Greenlee, and Cochise counties with 10-30 percent chances into Pinal, Santa Cruz, and eastern Pima counties. By Friday and this weekend, guidance weakens the influence of the upper level trough and precipitation chances come down a bit. Chances don`t completely fall off however with the potential for some tropical influence from the south. There is plenty of uncertainty in this scenario at this moment and the potential for tropical development off the western Mexico coast will need to be monitored. && .AVIATION...Valid through 21/12Z. Mainly SKC through 20/18Z, then FEW-SCT clouds 8k-11k feet with a 5-15% chance for -SHRA through 21/02Z. Surface winds light and under 12 kts through the forecast period. Surface wind direction west to northwest in the afternoon, otherwise terrain driven. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER... A modest increase in moisture today will bring minimum relative humidity values up to 20-30 percent in the lower elevations and above 30 percent in the mountains. An isolated shower can`t be ruled out this afternoon with the potential for a gusty downburst wind. Moisture values will increase 10-20+ percent, especially in Graham, Greenlee, and Cochise counties, from Tuesday through the end of the week. Chances for showers and thunderstorms will also arrive daily 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