Area Forecast Discussion
Issued by NWS Flagstaff, AZ
Issued by NWS Flagstaff, AZ
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658 FXUS65 KFGZ 201758 AFDFGZ Area Forecast Discussion National Weather Service Flagstaff AZ 1058 AM MST Thu Jun 20 2024 .SYNOPSIS...Daily chances for showers and thunderstorms are forecast through the weekend and into early next week, along with warming temperatures. && .UPDATE...Moisture from what is now Tropical Depression Alberto, located central Mexico, has pushed across the eastern third of Arizona. The deepest moisture and most unstable air mass according to model soundings will be along and north of a line extending from Heber to Show Low to Springerville and includes the Chuska Mountains, Defiance Plateau and the Chinle Valley. Storms today will move generally from south to north and will be capable of producing 0.50 to 1.00 inch downpours, wind gusts in excess of 50 mph and localized storm runoff. The western boundary of the moisture extends as far west as Flagstaff and Page but a mid-level cap of relatively warm air will likely result in extremely isolated storms that far west. && .PREV DISCUSSION /428 AM MST/...Today...A large area of high pressure sits over the eastern-half of the United States, with a trough situated over much of the west. Meanwhile, Tropical Storm Alberto is approaching the eastern coast of Texas and Mexico. As Alberto moves across Mexico, the trough over the west begins to lift northward and the ridge begins to retrograde. As a a result, a surge of sub-tropical moisture is initiated into Arizona. Surface dewpoints have already begun to rise into the 50s F and 60s F across much of New Mexico and into far eastern Arizona, as the moisture begins to inch closer to Arizona. PWATs look to rise to around 0.75-1.00 inches over Arizona by this afternoon, well above the 90th percentile for this point in the year. 00Z HREF guidances shows strong support for destabilization later this afternoon, with 700-1200 J/Kg of surface-based CAPE. 0-6km shear is a bit on the lower-end but with the influence of the trough, areas across northern Arizona could potentially see a few stronger thunderstorms with 25-35 kts of shear. Latest CAM guidance has the bulk of the activity this afternoon north of a Grand Canyon to St. Johns line, with lesser coverage along the Mogollon Rim as well. The greatest threat from this storms will be gusty outflow winds, brief heavy downpours, and small hail. However, a couple strong to severe thunderstorms can not be ruled out. Friday...The greatest moisture looks to move in on Friday, with PWAT values of around an inch for much of northern Arizona to upwards of 1.2 inches in the Lower Deserts. Even with the increased moisture, coverage still looks best over northern and eastern Arizona during the afternoon on Friday, and to a lesser extent over central Arizona. HREF and CAM guidance does show an increase in 0-6 km shear as the trough lifts northward. Thus, the threat for a couple of stronger thunderstorms remains. Localized flash flooding will also remain a possibility through the Four Corners region given the amount of moisture available, however storm motions of 20-25 kts may limit the residency time of any one storm. Saturday into Next Week...By the weekend the ridge has shifted full into New Mexico, moisture remains in place, keeping daily chances for showers and thunderstorms in the forecast. However, as the heights continue to rise with the ridge building into the Southwest, temperatures begin to warm once again for the start of next week. Coverage and intensity of showers and thunderstorms may begin to wain into next week as subsidence increases aloft. && .AVIATION...Thursday 20/18Z through Friday 21/18Z...Mainly VFR conditions persist through the TAF period with FEW-BKN cloud cover after 19Z. Expect isolated to scattered -SHRA/-TSRA from 20Z-03Z with brief periods of MVFR VIS and CIGS, confined along and east of a KGCN-KFLG-KPAN line. Showers and BKN clouds look to continue through the night near the Four Corners region. Anticipate south-southwest winds, 20-30 kts, becoming south 5-15 kts after 03Z. OUTLOOK...Friday 21/18Z through Sunday 23/18Z...Another round of scattered to widespread -SHRA/-TSRA is expected on Friday from 19Z-03Z with showers continuing into the night. Greatest coverage will likely be along the Utah and New Mexico borders. Moderate chances for -SHRA/-TSRA continue through the weekend across all of northern Arizona. Anticipate enhanced south to southwest winds on Friday afternoon, 20-30 kts, becoming much lighter for Saturday and Sunday, outside of any gusty outflows from storms. && .FIRE WEATHER...Today and Friday...Increasing chances for showers/thunderstorms from east to west today and Friday. South to southwest winds 15-25 mph, with gusty and erratic winds in the vicinity of storms. Increasing RH values from 15-30% today to 30-50% on Friday. Saturday through Monday...Chances for showers and thunderstorms each day. South to southwest winds around 5 to 10 mph Saturday and Sunday becoming more westerly at 5 to 15 mph Monday. Gusty and erratic winds possible in the vicinity of storms. Decreasing moisture will result in lower RH values, generally between 20-30%. && .FGZ WATCHES/WARNINGS/ADVISORIES...None. && $$ PUBLIC...McCollum/Humphreys AVIATION...LaGuardia FIRE WEATHER...Meola For Northern Arizona weather information visit weather.gov/flagstaff