Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
858 FXUS65 KTWC 292157 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 257 PM MST Tue Sep 29 2026 .SYNOPSIS... Bands of stronger showers and thunderstorms will continue across far eastern Arizona early this evening, ahead of a strong upper level disturbance moving in from southeast California, This will bring some additional bands of lighter rain showers to southern Arizona overnight and Wednesday morning, before drier air overtakes the state in the afternoon. Highs Wednesday will end up 10 to 15 degrees below normal, warming to near normal with light breezes late in the work week. && .DISCUSSION... The upper pattern this afternoon is characterized by a strong upper-low centered across southeast California and Hurricane Polo (a category 2 hurricane with maximum sustained winds of 75 mph near 28.0N/110.6W or over east-central Sonora Mexico, tracking NE at 15 kts). Polo remains forecast to rapidly weaken as it continues to weaken and accelerate toward the NE tonight, becoming a tropical storm over far west-cenral Chihuahua by 5 pm today. As of this writing, a band of training moderate to strong rain bands and embedded thunderstorms extends from Nogales, north-northeast to western Greenlee county, with area rivers/washes at Minor or Moderate flood stages, including the Gila, Brawley, Aravaipa Canyon and other locations including Sabino Creek and a low water crossing between mile marker 374 and 375 along highway 70 west of Duncan. The band results from a merger between that from the upper low cold frontal band and convective bands associated with the tropical storm moving into Chihuahua, Mexico. This will slowly translate east-northeastward across Cochise county, with several CAM`s continuing to depict at least two additional rounds of shower activity overnight which are focused into bands. The first should rotate through near midnight, while the second moves through through during the pre-dawn hours. CA upper low center continues to exhibit a southerly component to its track, allowing core convection to bring the additional rounds of showers overnight for us. Flow aloft will turn from northwest later tomorrow, allowing drier air advection into the region and a rebound in high temperatures to near normal under sunny to mostly sunny skies through at least weeks end. NBM medium and extended range forecasts hint at back door cold frontal development to our east concurrent with redevelopment or weak upper low over southeast NM. Low development would reinforce the gradient driven southeast winds along the Gila river and adjacent valleys, along with subtle moisture advection and afternoon convection. && .AVIATION /00Z WEDNESDAY THROUGH 00Z THURSDAY/... Valid through 01/00Z. Broad band of -SHRA/TSRA extends from OLS NNE over southern Greenlee county. SCT- BKN 010-015k ft AGL with BKN- OVC 030-06k ft AGL this this afternoon, with gradually decreasing cloud cover and storms this evening and overnight. Another round of light-moderate showers will move through around midnight, with a round of light showers expected during the pre-dawn hours. Generally VFR with brief MVFR possible under heavier showers/storms. MVFR CIGs possible early this evening with VIS down to 3-5 miles along with a slight chance of periods IFR for KOLS and KSAD. Gusty winds to 15 kts may some showers. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER... A strong upper-level weather disturbance in southeast California move into western Arizona early this evening. Additional rounds of lighter showers are a good possibility overnight given proximity of core convection to southern Arizona, before disturbance begins to moves east of the area Wednesday. Thereafter, dry conditions are forecast for the second half of next week. High temperatures will be 10 to 15 degrees below today and Wednesday, then warm back up to near normal late this week. Minimum RH values 35-55 percent in valley locations and 50-75 percent in the mountains today through Wednesday, generally lowering to 15-25 percent the second half of the week as drier air moves into the region. 20-foot winds will be less than 15 mph into mid-week, then gusty east to southeast winds possible the second half of the week. Breezy southwest to west winds will be possible along the surface front as it moves across the area today. && .TWC WATCHES/WARNINGS/ADVISORIES... Flood Watch until 11 PM MST this evening for AZZ501>515. && $$ SYNOPSIS...Tripoli DISCUSSION...Tripoli AVIATION...Tripoli FIRE WEATHER...Tripoli Visit us on Facebook, X, YouTube, and at weather.gov/Tucson