Area Forecast Discussion
Issued by NWS Tucson, AZ
Issued by NWS Tucson, AZ
318 FXUS65 KTWC 130938 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 238 AM MST Thu Jun 13 2024 .SYNOPSIS...Excessive heat continues today as high pressure results in very hot temperatures. Slight cooling Friday but temperatures still a few degrees above normal. Temperatures nudge upward again this weekend with an Excessive Heat Watch in effect for portions of southeast Arizona. Generally dry conditions through the forecast period with a just a slight chance for a sprinkle or light shower west of Tucson today, then shifting to Graham and Greenlee County tonight into Friday. && .DISCUSSION...Latest WV/IR satellite imagery shows partly cloudy skies across much of southeast Arizona with the region in southerly flow aloft between an upper ridge centered just to our east and a mid/upper low centered near 32N/120W off the southern California/northern Baja coast. This southerly flow will continue through the day and with the increased mid level moisture, there will be a continuation of mid level cloudiness streaming northward. PWAT values increase to around 0.8" but with a very dry sub-cloud layer it will be hard to get much more than some virga/sprinkles mainly west of Tucson during the day today. Convective parameters are pretty abysmal with MLCAPE values less than 100 J/KG so will be hard pressed to get lightning. Meanwhile, with more cloudiness today than was previously expected, that could temper down high temperatures a couple of degrees. For continuity sake and with some uncertainty on the clouds and its impact on temperatures, we continued the Excessive Heat Warning for today. Otherwise, expect some afternoon breeziness to go along with the hot temperatures today. As the mid/upper low moves into AZ late tonight into Friday, the modest mid level moisture plume will be shunted more towards locales to the north to northeast of Tucson, mainly in the higher terrain Graham/Greenlee Counties where a slight chance of sprinkles/light showers is expected. With the mid/upper low to our north Friday lowering heights/thicknesses, temperatures will cool just enough to be out of excessive heat criteria. However, with the slight cooling will come an uptick in winds which will be enough for fire weather concerns near the NM border. A Red Flag Warning has been issued for these locales. See fire weather discussion below for additional information. The mid/upper level pattern will reorient itself this weekend into next week and dominated by a strong subtropical ridge centered across northern Mexico, with southeast Arizona under dry westerly flow as broad troughing dominates much of the western US. Even though the ridge is centered to our south, height/thickness values support borderline excessive heat levels this weekend. Decided to hoist an Excessive Heat Watch for Saturday and Sunday for the deserts and up into Graham County to include the Safford area. Temperatures and heat risk is marginal, so later shifts can monitor trends and evaluate the need for upgrading to a warning. As the troughing to our north nudges heights down early next week, that will lower temperatures a few degrees. Expect afternoon breezes each day through the forecast period. Otherwise, the high will reorient itself a bit more to our east which could help introduce a bit more mid level moisture again by late next week. Otherwise, expect breezy afternoon winds for most days of the forecast period from the weekend through much of next week. && .AVIATION...Valid through 14/12Z. SCT-BKN clouds around 13k-20k feet AGL through much of the forecast period. Slight chances for virga/light sprinkles west of Tucson today, then shifting into Graham/Greenlee Counties tonight and Friday. SFC winds generally less than 12 kts early this morning, becoming WLY/NWLY 10 to 20 kts with higher gusts aft 13/18Z. The strongest winds will be near KSAD. Winds then subside aft 14/03Z to generally less than 12 kts. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Hot temperatures through the weekend, generally 5-10 degrees above normal. Limited mid-level moisture will result in a slight chance of sprinkles/virga or very light isolated shower activity mainly west of Tucson today, then shifting to the higher terrain northeast of Tucson tonight and Friday. Expect min RH values of 3-9 percent in the lower elevations and 7-15 percent in the mountains through this weekend, along with poor overnight recoveries between 20-35 percent in most locations. 20-foot winds will follow typical diurnal patterns, with afternoon/early evening gustiness due to strong surface heating. Sustained 20-foot wind speeds will generally be 15 mph or less today, though locally higher in the upper Gila River valley near Safford where near critical fire weather conditions are expected. Winds will increase a bit more Friday, focused on locales near the Arizona/New Mexico border. A Red Flag Warning has been issued for Zone 152 Friday where winds of 15 to 25 mph are expected and gusts up to 35-40 mph are possible. Elsewhere, expect elevated fire weather conditions Friday but winds below critical levels. Thereafter, breezes continue each day into next week with some afternoon gustiness Saturday, then perhaps another uptick with Monday having potential for wind speeds near critical levels. && .TWC WATCHES/WARNINGS/ADVISORIES... Excessive Heat Warning until 8 PM MST this evening for AZZ501>509. Excessive Heat Watch from Saturday morning through Sunday evening for AZZ501-502-504>506-509. Red Flag Warning from 11 AM to 8 PM MST Friday for AZZ152. && $$ Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson