Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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504 FXUS65 KRIW 151050 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 450 AM MDT Sun Sep 15 2024 .KEY MESSAGES... - Mainly dry today, with a breezy afternoon. Isolated (30% or less) showers and thunderstorms develop for western Wyoming this afternoon. Little rain expected, but strong outflow winds are possible. - A weather system pushes into the area Monday, with rain and mountain snow chances pushing east of the Divide late Monday through Tuesday. - A cold front moves through Tuesday, with cool temperatures and unsettled weather expected for the remainder of the week. && .DISCUSSION... Issued at 202 AM MDT Sun Sep 15 2024 The next weather system is approaching from the Pacific Northwest today, but main impacts won`t be until Monday and Tuesday. For today, flow shifts more southwest as the approaching trough moves in. This will continue to allow some warmer air into Wyoming, so highs today will climb up to 10 degrees warmer compared to yesterday. Some moisture ahead of the main system will spark some isolated (30% or less) showers and thunderstorms this afternoon west of the Continental Divide, and mainly for southwest Wyoming. Not expecting much, if any, rain to be falling with any of these showers. As tends to be the case, wind is the main hazard. Recent model runs are showing the potential for 50 mph outflow gusts, which dewpoint depressions would also support. Outside any storm outflows, afternoon winds increase, with gusts 15 to 25 mph for much of the area. Fire weather concerns are more limited today. Winds don`t look to be strong enough where relative humidities (RH) are critical, and RHs don`t get low enough where the strong winds will be. That being said, there could be some isolated areas of critical fire weather, especially where storm outflows occur. Will not being issuing any fire weather highlights, as favorable conditions do not look widespread enough. HREF also supports this, with less than 40% chance of critical fire weather conditions today; it does show some isolated, 60% to 70% chances, in the Bighorn Basin. Convection chances decrease tonight, but high-resolution models are showing some lingering over western Wyoming through the next morning. Confidence is not high in anything widespread, but have added some low POPs into the forecast to account for this outcome. Chances pick up again late Monday morning as the sun brings instability to the area. Again, the focus will be west of the Divide. Monday also brings another breezy afternoon, especially for southern portions of the area as a southerly flow occurs ahead of the upper-low. Speaking of, the upper-low tracks eastward through Monday, with the center reaching the Utah/Idaho border Tuesday morning. This brings precipitation chances east of the Divide late Monday and through the day Tuesday. A cold front also passes through Tuesday, bringing much cooler temperatures to the area. With 700mb temperatures dropping to around 0 to 2 degrees Celsius, snow levels around 9000 feet are expected. The low track over far northwest Wyoming through Tuesday and into central/eastern Montana Wednesday. This supports the best precipitation chances across western Wyoming, though everywhere will have a shot to see rain/high mountain snow. As this system exits Wednesday, another system is soon to follow. This one pushes more southward, into the Nevada area on Thursday. There is some model disagreement on exact placement. This low tracks eastward through Saturday. Highs at the end of this coming workweek range from around 60 to around 70. With this next system, temperatures look to fall a bit more for the weekend. Long range models are hinting at yet another low to move through around next Sunday, though this far out, would not put much confidence into that. && .DISCUSSION... Issued at 437 AM MDT Sun Sep 15 2024 VFR conditions through much of the period for all TAF sites. Light winds and mainly clear skies to start the period. Breezy south to southwest winds gusting to 18-25kts for all but CPR as the gradient increases with the next storm system nearing from the west. A round of scattered rain showers and isolated thunderstorms developing near RKS around 20Z before pushing north to BPI/PNA/JAC but with less confidence for LND/RIW/COD/WRL after 23Z. MVFR visibility possible and gustier winds with outflow winds in and around thunderstorms throughout the entire afternoon and evening Sunday. Diminished activity after 02-03Z with sunset as winds and cloud cover improves into the overnight hours into Monday morning. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Wittmann AVIATION...Lowe