Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
412 FXUS65 KTWC 182216 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 316 PM MST Tue Nov 18 2025 .SYNOPSIS... A low pressure system will cross the region over the next several days and bring cooler temperatures, chances for precipitation including snowfall above 7000 feet, and breezy conditions. Showers will be isolated to scattered through Wednesday morning, then becoming more widespread late Wednesday afternoon through early Thursday morning. Temperatures will become well below normal by Thursday with the first widespread freeze expected Friday morning, mainly in valleys to the south and east of Tucson. && .DISCUSSION... A pair of upper level lows will likely impact the region over the coming week, the first currently sitting over the southern California coast. This initial low places central to northern Arizona in an anomalously unstable and sheared environment this afternoon, leading to an active weather day in the Phoenix metro. Through the next 24 hours, mid-level height falls will overspread southeastern Arizona while a plume of subtropical moisture orients itself over the area. Shower chances should gradually increase tonight as this process occurs, but the strongest chances will arrive Wednesday afternoon and persist through early Thursday as the upper trough crosses the region. Rain will likely be convective in nature for much of this event which will lead to some hit or miss scenarios in regard to precipitation totals, but overall the forecast spread remains in the 0.33-0.67 inch range across lower elevation locations and 0.67-1.25 inches in the Sky Islands and White Mountains. Snow levels will likely fall late Wednesday and early Thursday with accumulating snow of 2-5 inches above 7500 feet in the Sky Islands near and north of Tucson with 4-7 inches possible atop Mt Graham and the White Mountains. Isolated rain totals exceeding one inch can`t be ruled out, especially where pockets of thunderstorms develop. One threat that also can`t be ruled out is the potential for stronger thunderstorms, which will be heavily dependent on how much instability forms Wednesday. With ample shear provided by the potent trough aloft, low-topped thunderstorms may provide a small hail threat given adequate daytime heating. The upper trough should kick out fairly quickly on Thursday with moisture exiting the region late in the day. Light showers may linger through the afternoon but the bulk of the precipitation should be done by the morning. Cold and dry air will push in and produce quite the chilly morning Friday. The first widespread freeze potential of the season should arrive Friday morning across valleys south and east of Tucson. This will be especially true across the Sulphur Springs Valley where a hard freeze is looking increasingly likely. The one caveat will be how well does moisture exit those valleys, but if trends continue a freeze headline will be needed. The aforementioned second low should drop in through the west coast towards northern Baja by Saturday. This will keep unseasonably cold temperatures in place through early next week along with bringing chances for rain and high elevation mountain snow Saturday and Sunday. && .AVIATION...Valid through 20/00Z. Increasing ceilings at 4k-7k feet tonight with isolated to scattered showers across much of southeastern Arizona. Can`t rule out isolated near MVFR ceilings especially south at KOLS-KDUG. Surface winds diminish this evening, then increase out of the south Wednesday after 19/15Z. Winds of 14-18 kts at KOLS-KDUG and 8-14 kts at KTUS up through KSAD. Showers to become more widespread with lowering ceilings likely Wednesday afternoon through early Thursday. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER... A storm system will begin to impact Southeast Arizona this afternoon/evening across central and western Pima county, then the rest of Southeast Arizona Wednesday into Thursday. This system will bring numerous showers with a slight chance of thunderstorms, snowfall to the mountains above 7000 feet, well below normal temperatures and breezy south to southwest winds. Isolated to scattered rain showers will likely become widespread from late Wednesday afternoon through early Thursday morning. Minimum RH values will be well above critical levels over the next week, with values generally 35-45 percent in the valleys and 65-75+ percent in the mountains. && .TWC WATCHES/WARNINGS/ADVISORIES... None. && $$ Public...Edwards Aviation...Edwards Fire Weather....Edwards Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson