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Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
691 FXUS65 KTWC 151617 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 917 AM MST Thu Aug 15 2024 .SYNOPSIS...Generally dry and hot today with a slight chance of a shower or thunderstorm along the International Border and in the mountains of southeastern Arizona. Thunderstorm chances then return areawide Friday and continue through at least early next week. High temperatures will be above normal into next week. && .UPDATE...The 15/12z 500 mb upper air plot showed sub-tropical ridge over the southern tier of states with one upper high centered over SW AZ and a second one central Texas. Dry N-NE flow over the area with precipitable water value (PW) of 1.21" on the 12z Tucson sounding which is down about 0.25" from Wednesday morning. Overall across SE AZ, PW values ranged from 0.90" near AZ/NM border to 1.25" west of Tucson. Surface dewpoints ranged from the mid 50s to the mid 60s at 9 am while satellite imagery showed a clear sky. For today, any storm activity this afternoon/early evening will be near the mountains along the Intl border. Highs today will run up to 5 degrees above normal. See previous discussion below for further details on scattered storms returning to the area tomorrow into the weekend. && .PREV DISCUSSION... /issued 243 AM MST Thu Aug 15 2024/ Upper level objective analysis depicts a high pressure center from southern California through southern Arizona. This center will be ushered east over the coming 36 hours as a Pacific Northwest trough deepens and nudges the ridge axis into New Mexico. Today, high temperatures are expected to be 3 to 6 degrees above average for this time of year thanks to the warming ridge pattern aloft and clearer skies. Shallow instability will allow for some afternoon cloud build ups with potentially an isolated thunderstorm over the southern mountains, but otherwise a stout mid- level cap keeps the forecast mostly dry. Friday the ridge centers over New Mexico, cooling temperatures in the mid levels a few degrees and returning moisture with southeasterly flow. Both will contribute in bringing thunderstorm chances back to southern Arizona, though areas in Pinal, Graham, and Greenlee counties (outside of the White Mountains) may struggle to see much with the upper high still in the vicinity. Friday may be worth watching for a potential severe wind gust day, depending on details with the pattern transition. Dry mid-levels would allow for evaporative cooling enhancements of downbursts and the forecast presence of 20 knot winds at 500mb may aid in producing longer lived thunderstorm cells. The lingering presence of the mid-level cap from the nearby ridge will impact thunderstorm coverage and potentially intensity, so there remains some uncertainty in the severe hazard ceiling. Through the weekend the upper high remains generally in place to the east, keeping southeastern Arizona under favorable southeasterly flow for moisture transport and thunderstorm impacts. Though there is some wobbling in amplitude and location, ensemble solutions generally keep this pattern going through next week. This produces daily chances for thunderstorms with likely day to day variance in coverage with the shifting of the upper level high. && .AVIATION...Scattered clouds at 7k to 10k feet AGL from 15/18Z to 16/03Z, especially across KOLS- KDUG terminals. Slight chance of -SHRA or -TSRA across the south during this period as well. Clearing skies after 16/03Z. Erratic wind to 40 kts with -TSRA. Otherwise wind 12 kts or less favoring west to northwest direction during the day, then light and variable late.Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...A slight chance of a thunderstorm in the mountains mainly south and southeast of Tucson today, with dry conditions expected elsewhere. Moisture then returns Friday into next week, with a daily chance of showers and thunderstorms across much of southeastern Arizona. High temperatures will be 3 to 6 degrees above normal through at least early next week. Min RH values will be in the 20-30 percent range in most valleys locations (lowering to near 15 percent in eastern Cochise and the upper Gila River valley) through early next week. Outside of any 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. && $$ Public...Public Forecaster Aviation...Aviation Forecaster Fire Weather....Fire Weather Forecaster Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson