Area Forecast Discussion
Issued by NWS Flagstaff, AZ
Issued by NWS Flagstaff, AZ
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039 FXUS65 KFGZ 211730 AFDFGZ Area Forecast Discussion National Weather Service Flagstaff AZ 1030 AM MST Fri Jun 21 2024 .SYNOPSIS...Look for daily chances for showers and thunderstorms over the weekend and into the middle of next week. Otherwise, muggy and hot conditions will continue. && .UPDATE...Model soundings are indicating and mesoscale forecast models are showing a downturn in shower and thunderstorm activity today compared to Thursday. The main change to the forecast for today was to lower the chance of showers and thunderstorms across the area near the Arizona/Utah border and Four Corners. Otherwise, look for hot and somewhat muggy weather to continue as we make our first foray into a true monsoon pattern. && .PREV DISCUSSION /430 AM MST/...Today...The remnants of Tropical Storm Albert continue to pump moisture northward into Arizona. While at the same time, a trough over the Great Basin begins to lift into the Northern Rockies today and high pressure builds into the southwest from the east. 00 UTC HREF guidance has around 800-1200 J/Kg of surface-based CAPE over much of the area, with the highest amounts most likely near the AZ/UT border. Given the influence of the trough, 0-6km bulk shear looks to increase today, with 35-45 kts expected near the AZ/UT border. This added shear and instability will allow for more organized thunderstorms this afternoon, with a few strong to severe storms capable of producing damaging winds and hail likely. Elsewhere, shear begins to weaken rapidly, with generally 20 kts expected, favoring less organized thunderstorms across the rest of the region. Given PWATs in the 0.80-1.20 inch range, heavy rainfall will be possible and could lead to areas of localized flash flooding. However, given storm motions of around 25-30 kts, the residency time of any one storm will be limited. Therefor, the flash flood threat is largely limited to any flood sensitive areas (slot canyons, recent burn scars, and urban areas) or locations where training thunderstorms occur. HREF PMM guidance shows the greatest risk for heavy rainfall will mainly be across far northern Arizona into the Four Corners region, where better forcing looks to be available. All and all, the greatest chances for showers and thunderstorms this afternoon and evening will be north of a Grand Canyon to St. Johns line. More isolated coverage is expected across the Mogollon Rim. Saturday and Sunday...After the trough lifts, high pressure will continue to build eastward into Arizona. Moisture remains trapped under the ridge, so daily chances for showers and thunderstorms will continue. However with weaker forcing in place, less organized thunderstorm activity is expected. While at the same time, the threat for flash flooding increased with slower storm motions and increased moisture. Coverage areas also look to shift to the higher terrain, where given the lack of synoptic forcing, orographic forcing will aid convective initiation. Monday through Thursday...Heights continue to rise into next week as high pressure becomes centered over Arizona and New Mexico. Moisture remains in place, so chances for showers and thunderstorms will remain in the forecast. However, coverage will begin to wain each day into next week. Temperatures look to rise, with the potential for excessive heat across the lower elevations by the middle of next week. && .AVIATION...Friday 21/18Z through Saturday 22/18Z...Mainly VFR expected. MVFR in SHRA/TSRA between 18Z-03Z, mainly along and east of KGCN-KPAN line with ISO SHRA through 12Z/Sat. S-SW winds 15-25 kts with gusts 30-40 kts. Erratic and gusty winds in the vicinity of storms. OUTLOOK...Saturday 22/18Z through Monday 24/18Z...Mainly VFR expected. Expect SHRA/TSRA between 18Z-03Z each day. S-SW winds 5-15 kts each afternoon. Erratic and gusty winds in the vicinity of storms. && .FIRE WEATHER...Today and Saturday...Scattered to widespread showers and thunderstorms each afternoon with showers continuing overnight. Wetting rains are likely with any storms along with gusty and erratic outflow winds up to 45 mph. Outside of outflow winds, south to southwest winds at 25-35 mph today with lighter winds at 10-15 mph Saturday. Sunday through Tuesday...Chances for showers and thunderstorms continues through Monday, mainly along and south of the Mogollon Rim and the White Mountains. Isolated to scattered activity on Tuesday, mainly along the higher terrain. Temperatures remain seasonal with light southwesterly flow around 10-15 mph each afternoon. && .FGZ WATCHES/WARNINGS/ADVISORIES...None. && $$ PUBLIC...McCollum/Humphreys AVIATION...RR FIRE WEATHER...Meola For Northern Arizona weather information visit weather.gov/flagstaff