Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
978 FXUS65 KTWC 091024 CCA AFDTWC Area Forecast Discussion...CORRECTED National Weather Service Tucson AZ 324 AM MST Tue Jul 9 2024 .SYNOPSIS... Excessive heat continues across southeastern Arizona with high temperatures expected to approach record levels today through potentially Thursday. Moisture will gradually return over the next several days, ushering in chances for thunderstorms beginning this afternoon. && .DISCUSSION... During the overnight hours, an increase in lower level moisture through Graham, Greenlee, and Cochise counties was evident in a rapid rise in observed surface dew points as well as modeled by RAP guidance`s rise in mean mixing ratio through 100mb (depicted on SPC`s mesoanalysis page). This rise in low level moisture, heavily contributed by thunderstorm outflows from New Mexico, will lead to more favorable instability for thunderstorm activity this afternoon and evening. The instability gradient should fall off towards the Tucson area, therefore better chances for convection today lie east of Tucson (though an isolated cell in the Tucson area can`t be ruled out). Under strong surface heating and a very well mixed boundary layer, isolated strong outflow winds will be possible with any thunderstorm today. Speaking of surface heating, excessive heat is expected to continue across much of southeastern Arizona today through at least Wednesday. As multiple daily temperature records fell yesterday, the same will be possible again today (record temperature information included below). NBM probabilities indicate around a 60% chance of reaching 110 degrees in Tucson today and Wednesday, with a nudge down on Thursday. The excessive heat probabilities on Thursday come with an added wrinkle of the increasing moisture and thunderstorm potential, which adds uncertainty to how hot the afternoon may get. The Excessive Heat warning continues through tomorrow, but further evaluation on a possible extension into Thursday will be needed. Through the remainder of the week, the center of the upper level high is expected to shift from southern California towards Colorado. The associated gradual turn of the mean flow to become easterly will bring richer lower to mid level moisture into southeastern Arizona, advancing westward day by day. With mean flow initially from the north-northeast through Thursday, southward thunderstorm motions will bring activity off the Mogollon Rim through southeastern Arizona each afternoon and evening. Then Friday through the weekend, with the upper high parked to the north and richer atmospheric moisture in place, thunderstorm chances will be well distributed across southeastern Arizona each day. The 00Z deterministic suite along with ensemble QPF probabilities continue to highlight Sunday-Monday as particularly active days as models bring a stronger easterly wave into the region, though uncertainty remains as orientation of the upper high or previous day activity will impact each day`s convective potential. && .AVIATION...Valid through 10/12Z. Mostly SKC with a few cirrus clouds this morning, then scattered cumulus AOA 10k-12k feet after 09/20Z. Isolated to scattered thunderstorms this afternoon and evening, generally east of KTUS. Strong, gusty outflows possible with any thunderstorm today. Otherwise generally west to northwest winds to around 10 kts with occasional afternoon gusts up to 20 kts. Winds become light and terrain driven after 10/03Z. Aviation discussion not updated for TAF amendments. 20 foot winds of 12 to 16 mph with gusts to around 25 mph are expected each day with light and terrain driven winds overnight. Isolated to scattered showers and thunderstorms should develop each afternoon through Thursday, with more widespread chances starting Friday into early next week. Strong outflow winds will be possible with any thunderstorm. && .FIRE WEATHER... Excessive heat continues across the majority of southeast Arizona. Minimum relative humidities today through Thursday will generally fall into the 10 to 16 percent range in the lower elevations and 15 to 30 percent in mountain areas. Moisture will increase Friday through the weekend with higher relative humidities. 20 foot winds of 12 to 16 mph with gusts to around 25 mph are expected each day with light and terrain driven winds overnight. Isolated to scattered showers and thunderstorms should develop each afternoon through Thursday, with more widespread chances starting Friday into early next week. Strong outflow winds will be possible with any thunderstorm. && .CLIMATE... Near record to record high temperatures today, Wednesday, and Thursday. DATE Jul 09 Jul 10 Jul 11 FCST RCD/YR FCST RCD/YR FCST RCD/YR TUCSON INTL AIRPORT 110 110/1979 110 109/2021 110 111/1958 PICACHO PEAK 113 113/1994 112 111/1995 111 112/1998 SAFFORD AG STATION 106 108/1956 107 110/2003 106 110/2019 SIERRA VISTA FD 100 103/2003 100 102/2003 100 103/2020 && .TWC WATCHES/WARNINGS/ADVISORIES... Excessive Heat Warning until 8 PM MST Wednesday for AZZ501>506- 509. && $$ Public...Edwards Aviation...Edwards Fire Weather....Edwards Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson