Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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835 FXUS65 KRIW 300432 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1032 PM MDT Sat Jun 29 2024 .KEY MESSAGES... - Above normal temperatures, a dry lower atmosphere, and gusty southwest wind elevates the fire weather hazard Sunday. Critical fuels in Natrona County have led to a Red Flag Warning Sunday afternoon. - Seasonal temperatures return Monday behind a cold front. Scattered thunderstorms are most likely across the northern- third of the forecast area. - After a period of generally seasonal temperatures and typical afternoon showers and thunderstorms, a ridge of high pressure will raise temperatures for next weekend while keeping conditions dry. && .DISCUSSION... Issued at 122 PM MDT Sat Jun 29 2024 Satellite imagery shows isolated convection across northeast Utah early Saturday afternoon within a plume of mid-level moisture. Southwest flow aloft allows this plume to track into southwest Wyoming later this afternoon. Given low dew points and limited instability, any convection would be weak with little if any rainfall and generally confined to Sweetwater County until sunset Saturday. Gusty outflow wind 40 to 50 mph would be the primary hazard with any convection. Otherwise, dry conditions and seasonal temperatures prevail overnight as a low-amplitude ridge axis traverses the region. The upper flow backs a bit more to the southwest Sunday in response to an approaching trough moving across the Pacific Northwest and into the Northern Rockies Sunday and Sunday night. Southwest wind of 20-30kts at 700mb mixes to the surface during the afternoon ushering in drier air from the southwest. This same flow boosts 700mb temperatures to 16-18C Sunday afternoon leading to widespread highs in the 90s. Dew points decrease through the afternoon hindering convection and dropping relative humidities into the teens. This favors elevated fire weather conditions across central and southwest Wyoming. One limiting factor to realizing full heating and low humidity could be afternoon cloud cover within this region. The axis of mid-level moisture remains along and south of a line from roughly Green River to Kaycee, where cloud cover may become a bit more extensive Sunday afternoon. Isolated convection is most plausible across the eastern half of Natrona County and neighboring areas. The incoming trough and associated cold front reaches northwest Wyoming Sunday evening and pushes east overnight and into Monday morning. Scattered showers and a rogue thunderstorm or two develop as moisture spreads across the northern-third of the forecast area. Jet streak energy and a steady stream of channeled vorticity serves to enhance convective potential through the day Monday, especially across the aforementioned northern areas. Daytime high temperatures Monday cool 8-15F from those of Sunday. Below elevations of 6000 feet, the coolest readings will be across the far north where readings may not climb out of the 70s. The trough lifts northeast late Monday night leading to a decrease in precipitation by sunrise Tuesday. Overnight temperatures will be seasonal. Cyclonic flow lingers Tuesday keeping daytime highs below normal by 5-8F at many locations, particularly along and east of the Continental Divide. The far north has the best chance for showers given the persistent cyclonic flow. Temperatures moderate a bit for Wednesday, but the last vestiges of the cyclonic flow keeps the threat of late day convection over the far north through Thursday. There is also a hint that a surface boundary will push across areas east of the Continental Divide and cool daytime highs for Independence Day. The pattern does begin to show signs of shifting Friday into Saturday as ridging builds along the West Coast. The overall trend will be toward drier and warmer conditions beginning Friday on into the weekend. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1031 PM MDT Sat Jun 29 2024 All terminals to be VFR through the forecast period. Mainly high clouds to drift across the region overnight. Upper flow backs to the southwest Sunday and winds increase ahead of an approaching trough. Southwest wind 15-30kts develops at most terminals between 16Z-20Z/ Sunday with much drier air filtering into the region. Mid-level moisture does track into portions of central and southwest Wyoming Sunday afternoon. Isolated high-based showers develop around 20Z/Sunday with potential impacts from gusty outflow wind, with the best chance (<20 percent) at KCPR and KRKS. Convection and gusty winds decrease 02Z-03Z/Sunday. A surface boundary brings northerly surface wind to the Bighorn Basin terminals Sunday evening. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on smoke, icing, and turbulence forecasts. && .FIRE WEATHER... Issued at 122 PM MDT Sat Jun 29 2024 Unseasonably warm temperatures and gusty southwest wind 20 to 35 mph will combine to create low relative humidities Sunday afternoon leading to widespread elevated fire weather conditions. A Red Flag Warning has been posted for Zone 280 where fuels are now critical. A dry lower atmosphere will hinder the development of late day showers and thunderstorms. Any that are able to form would generate outflow wind gusts of 40 to 50 mph rather than rain of any consequence. Conditions improve around sunset Sunday and more so Monday behind a Sunday night cold front. && .RIW WATCHES/WARNINGS/ADVISORIES... Red Flag Warning from 1 PM to 7 PM MDT Sunday for WYZ280. && $$ DISCUSSION...CNJ AVIATION...CNJ/LaVoie FIRE WEATHER...CNJ