Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
193 FXUS65 KTWC 182150 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 250 PM MST Fri Jul 18 2025 .SYNOPSIS...Low-grade monsoon pattern through the weekend with high temperatures around normal. && .KEY MESSAGES... -Scattered showers and storms this afternoon and evening mainly south and east of Tucson with the main hazard being heavy rainfall. -Chances (30-50%) for scattered showers and thunderstorms continue into the overnight hours mainly east of Tucson. -A gradual warming and drying trend is expected by the latter half of next week. Increasing temperatures and decreasing chances for precipitation will lead to widespread Moderate HeatRisk and below normal precipitation. && .DISCUSSION...Latest GOES-19 satellite imagery showed scattered cumulus development over southeast Arizona. A few showers and storms have been trying to pop up over the higher terrain areas from orographic convergence, but struggling to stay organized. This could partially be attributed to a layer of warm air aloft (per the 18/18Z KTWC sounding) choking off updrafts. The 18/18Z sounding from KTWC also came back with around 1.2 inches of precipitable water (drier than anticipated) but there is still better moisture residing and moving into Cochise County according to GOES-19 precipitable water trends over the last few hours. There was also drier air aloft on the sounding with mid-level relative humidity around 40 percent. Latest RAP and other short term guidance shows increasing midlevel relative humidity to around 70 percent this afternoon along the Arizona and New Mexico border. Over the next few hours, midlevel positive vorticity advection in conjunction with upper level diffluence and a relative weakness in the midlevel will begin to interact with the low to midlevel moisture resulting in better dynamic forcing for scattered showers and storms. The strongest dynamic forcing will gradually shift north into Graham and Greenlee counties around 03Z (8 pm) which could help initiate additional convection and sustain some storms into the evening to the east of Tucson overnight. Any stronger storms from this activity could result in heavy rain and isolated instances of Flash Flooding. From Tucson west, latest guidance does not support the confidence or coverage for showers and thunderstorms, so nudged the probability or precipitation down from NBM guidance where appropriate. Over the weekend, southerly flow continues with the upper low moving into southern California and the high pressure centered over the southeast coast. This will be conducive to additional low to mid grade Monsoonal thunderstorm activity (mainly east of Tucson) with daily chances for isolated to scattered afternoon thunderstorms. There will be continued potential for heavy rain which could result in localized instances of flash flooding, and perhaps gusty outflow winds in the strongest storms. Heading into next week, low grade Monsoon days continue. However, we will see a gradual drying trend as ensembles are starting to show moisture get shunted gradually eastward. Afternoon shower and thunderstorm potential will mostly be dependent on recycled moisture from thunderstorm outflows from the previous day. Latest guidance from the Climate Prediction Center depicts above normal temperatures and below normal precipitation for southeast Arizona in the 6 to 10 and 8 to 14 day outlooks. Temperatures will be on the increase with highs starting to rise to a few degrees above normal areawide by the beginning of next week. By midweek, we see high pressure rebuilding into the Desert Southwest resulting in widespread moderate HeatRisk and notably lower chances for storms. && .AVIATION...Valid through 20/00Z. FEW-SCT cloud bases at 8k-11k feet with isolated to scattered showers and thunderstorms mainly east and south of KTUS through this evening. Gusty and erratic winds up to 40 kts with any storm. Otherwise surface winds mainly under 12 kts. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...High temperatures near normal for much of the next 7 days. Low grade monsoon pattern for much of the next 7 days with day-to-day variability in thunderstorm coverage. Afternoon winds will remain westerly from 10-15 mph, with occasional gusts at or above 25 mph. Afternoon RH values in the low lying areas will be 20- 30% through Friday decreasing to 17-25% over the weekend. In the higher terrain, RH will be around 30 to 50%. && .TWC WATCHES/WARNINGS/ADVISORIES...None. && $$ Public...DVS Aviation...Edwards Fire Weather...DVS Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson