Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
921 FXUS65 KTWC 131745 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 1045 AM MST Tue Aug 13 2024 .SYNOPSIS... Isolated to scattered thunderstorms are expected this afternoon and evening with the potential for heavy rain and strong wind gusts. Chances for thunderstorms decrease Wednesday and Thursday. High temperatures will rise a few degrees above normal through the second half of the week. .UPDATE... Clearer skies across the majority of southeast Arizona this morning compared to the last few mornings will give way to strong daytime heating. Dew points were in the upper 50s to low 60s in the past hour with a drying trend out east as we warm. No deviations from the short term forecast are anticipated this morning with the latest 13/12Z HREF model and TWC sounding. 1.6 inches of precipitable water was observed in the morning sounding which is right at the 75th percentile. DCAPE was right around 1100 J/kg which is up compared to yesterday, although shear is a bit more modest leading to an environment favoring pulse thunderstorms. HREF is highlighting areas generally east and south of Tucson this afternoon with isolated to scattered thunderstorms, but not sending any strong signals for severe wind or flash flooding concerns. Storms will tend to initiate over the higher terrain around 11 AM to 1 PM before becoming primarily outflow driven and moving into the valleys thereafter. Overall, looking like an average Monsoon day focused over areas generally south and east of Tucson with isolated to scattered pulse thunderstorms this afternoon. A couple storms may produce strong gusty winds and heavy rainfall, especially with any cell mergers. Refer to the previous discussion below for long term forecast details. && .PREV DISCUSSION... /issued 230 AM MST Tue Aug 13 2024/ .DISCUSSION... As a weak mid-level shortwave sits over southern Arizona, thunderstorms are again expected this afternoon and evening across southeastern portions of the state. As the shortwave should nudge east through the day, so will the moisture axis and expected coverage. Though isolated thunderstorms will still be possible in central to western Pima and Pinal counties, chances should be lower than Monday. Otherwise, scattered thunderstorms will provide chances for typical monsoon hazards of heavy rain and strong winds. Neither hazard has a notable signal however from high-res guidance. Isolated flash flooding threats may arrive with thunderstorm collisions, with individual cells likely moving quick enough to keep heavy rainfall durations low on their own. A chance of strong to severe wind gusts will accompany any thunderstorm as well given the mid-level dry air on forecast soundings and the 00Z RAOB, though weaker shear and modest DCAPE is likely contributing to the lack of greater wind gust probabilities from the high resolution model ensemble. Following today, a mid to upper level high pressure circulation will move west to east over southern Arizona through Friday. This will initially act to suppress convection chances as moisture is pushed south and mid-level temperatures warm. A few thunderstorms will be possible Wednesday along southern areas of Santa Cruz and Cochise Counties, while Thursday`s forecast is virtually dry with the high pressure center directly overhead. This pattern shift will also bring high temperatures up a few degrees above normal from Wednesday into the weekend. Precipitation chances begin to increase Friday as moisture returns with the upper high shifting east and mean flow turning east to southeasterly. There remains uncertainty in how quick this moisture returns Friday, with ensembles showing better precipitable water probabilities over the weekend. At this time just 15 to 30 percent precipitation chances are in the forecast Friday afternoon and evening and mainly south of Tucson to Willcox, as well as slight chances on mountain ranges. Greater coverage arrives on Saturday. && .AVIATION...Valid through 14/12Z. Scattered to broken ceilings at 7k to 10k with isolated to scattered TSRA from 13/19Z to 14/03Z. Visibility restrictions, gusts to 45 kts, heavy rain, and mountain obscurations likely with any thunderstorm. Wind outside of thunderstorms will be less than 12 kts and favor a west to southwesterly direction. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER... Isolated to scattered thunderstorms expected again this afternoon and evening. A downturn in thunderstorm chances is likely Wednesday and Thursday, with moisture and thunderstorms returning by the weekend. Temperatures warm a few degrees above normal the second half of the week. This trend brings minimum relative humidities down to around 15 to 25 percent in the valleys. Outside of thunderstorm outflow winds, 20-foot winds will generally be 15 mph or less, with afternoon/early evening gusts to 20-25 mph and light winds overnight. && .TWC WATCHES/WARNINGS/ADVISORIES...None. && $$ Update...DVS Prev Discussion...Edwards Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson