Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
393 FXUS65 KTWC 011547 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 847 AM MST Mon Sep 1 2025 .SYNOPSIS...Isolated thunderstorms possible today with any thunderstorm potentially producing gusty winds and briefly heavy rain. Daily chances for thunderstorms continue this week with day to day variability. High temperatures will be near normal through mid- week, then become below normal the second half of the week. && .UPDATE...Mid-level clouds cover most of southeast Arizona and will stick around through the morning. Today looks to be a low grade monsoon day with hi-res guidance showing isolated convection in the White Mountains, along the international border, and part of western Pima County. Best chances will be in the White Mountains. Mid-level flow will be out of the east today bringing slightly dryer air into areas east of Tucson and beginning to moisten up areas west of Tucson. These easterly winds will push any storms that form over the White Mountains and Rim into Gila and Pinal Counties rather Graham and Cochise Counties like yesterday. A weak vort max will be moving through northern Sonora and could provide extra support for storms along the international border and western Pima County. Storms will be capable of strong gusty winds and brief heavy rainfall. For longer term details see the previous discussion. && .PREV DISCUSSION... /issued 331 AM MST Mon Sep 1 2025/ Moisture has moved through Pinal and western Pima early this morning with surface dew points 5-10 degrees higher than they were 24 hours ago at this time. Easterly flow will keep the richer moisture field west of Tucson today, with some drying occurring eastward through the New Mexico border. With the moisture and instability field to the west, overall thunderstorm development may struggle today. This afternoon should see some thunderstorms develop over the White Mountains, then push west to southwest. With steering winds taking a more easterly than southeasterly component, these thunderstorms will be more favored to move towards Pinal and Gila counties rather than southwest towards Tucson. Additional thunderstorms developing over mountainous areas of southeastern Tucson can`t be ruled out, however the aforementioned dry air nudging in from the east will limit this activity. An easterly impulse will continue to drift to the west over northern Sonora, providing potentially additional lift for thunderstorms over Santa Cruz through western Pima county. Whether or not this wave is far enough north to bring chances into far southern Arizona is uncertain however, and lingering cloud cover from overnight convection may limit initiation this afternoon- evening anyway. Forecast chances generally in the 15-30 percent range, with greater chances this afternoon in the White Mountains. With drier air moving in, forecast instability parameters are a bit weaker than Sunday, with less of a signal for strong winds. If outflows for thunderstorms off the White Mountains can become organized there may be an opportunity for wind gusts through northern Graham and Pinal counties. A similar moisture layout remains Tuesday and Wednesday, with subsequent thunderstorm chances mainly focused on Santa Cruz and central to western Pima (as well as the Whites). Thursday into the weekend sees increasing thunderstorm chances with continuing potential for tropical moisture to make its way into southeastern Arizona. Model to model and run to run consistency in the east- west track of a possible tropical system (forecast for formation from the NHC at 80% in the coming week) remains very low, but will be worth watching for a heavy rain threat. && .AVIATION...Valid through 02/12Z. Isolated showers and thunderstorms this afternoon and evening, with greater coverage more likely south and west of KOLS. Surface winds today become southeasterly and 10-15 kts with gusts to 25 knots. Aviation discussion not updated for TAF Amendments. && .FIRE WEATHER... Minimum relative humidity values generally above 20-30 percent across southeastern Arizona through the week. Near normal temperatures through mid-week, then lower than normal the second half of the week. Winds today out of the east to southeast at 12 to 17 mph with gusts of 20 to 30 mph, especially in areas open to easterly flow such as the Gila River Valley. Southeasterly winds continue Tuesday then become lighter mid-week. Isolated thunderstorms today, with greater chances over the White Mountains and in far southern locations including Santa Cruz through western Pima counties. Daily chances continue this week with day to day variability. && .TWC WATCHES/WARNINGS/ADVISORIES... None. && $$ Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson