Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
519 FXUS65 KTWC 111018 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 318 AM MST Tue Nov 11 2025 .SYNOPSIS... High temperatures remain several degrees above average through Thursday. A low pressure system is then expected to cross the region Friday through the weekend, bringing chances for rain and high elevation mountain snow, cooler temperatures, and windy conditions. && .DISCUSSION... After a chilly morning in the eastern valleys, temperatures bounce back up today to above normal as an upper level ridge drifts over the region. Over the coming several days an upper trough currently over the Gulf of Alaska is expected to dig south, likely crossing the west coast and reaching the desert southwest Friday to Saturday. Global model ensemble members are showing increasing consistency in handling the evolution of the upper trough, with most closing off the base of the trough as it begins to cross the upper Baja. A cutoff low often presents challenges in forecasting timing or precipitation totals, and in this case there should remain a medium sized grain of salt in what to expect Friday through the weekend. Looking at what the 00Z deterministic suite is showing synoptically, an upstream jet ejects a speed max through the base of the low as it approaches. In that outcome it`s reasonable to see how that jet streak associated with the crossing low brings strong ascent to produce notable precipitation chances and potentially periods of moderate rates. However there remains the potential for the low to delay its arrival or arrive weaker than many ensemble members are showing, which is reasonable as well given the likelihood that it closes off. The ensemble spread in QPF at any one location remains fairly high given these uncertainties, ranging from just very light amounts to over an inch (with an even greater values at elevation). The high end of the probabilistic envelope has increased in recent model runs as more ensembles are latching onto the solution that features a stronger low, which does introduce the possibility for minor flooding impacts. Short- term rainfall rates aren`t likely to cause notable flooding concerns on their own, but areas under the exit region of the upper jet may see a prolonged period of moderate precipitation that could cause street ponding and running water through washes. Currently the favored track is tending to bring heaviest rainfall totals north of Tucson, closer to Phoenix and north...but periods of moderate precipitation can`t be ruled out for any location of southeastern Arizona. Accumulating snow atop mountains should also arrive with this low, mainly above 7500 feet. If sufficient moisture wrap- around occurs as the low crosses late Saturday, snow levels may drop a bit lower. Current forecast totals remain below advisory criteria but 6 inch accumulations or more can`t be ruled out in the White Mountains. Temperatures will significantly drop with this system and southwest winds will increase Friday into the weekend. Highs Saturday will likely fall 10-15 degrees below normal and potentially even lower in areas that see prolonged precipitation. Temperatures remain below normal Sunday into early next week with just a modest rebound as the low exits. A risk of sub- freezing morning lows Sunday through Tuesday will return for valleys east of Tucson. && .AVIATION...Valid through 12/12Z. Mainly SKC with a few high level cirrus streaming through the area. Winds light, terrain driven, and under 10 kts through the forecast period. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER... Light terrain driven winds mainly under 12 mph through Wednesday with minimum relative humidities of 12 to 22 percent. A low pressure system will likely cross the region Friday through the weekend. Winds will begin to increase ahead of this system Thursday and especially Friday. Widespread rain and high elevation mountain snow chances overspread the region Friday and Saturday. Temperatures are expected to become well below normal over the weekend. && .TWC WATCHES/WARNINGS/ADVISORIES... Freeze Warning until 9 AM MST this morning for AZZ507>509. && $$ Public...Edwards Aviation...Edwards Fire Weather....Edwards Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson