Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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782 FXUS65 KRIW 301132 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 532 AM MDT Tue Apr 30 2024 .KEY MESSAGES... - Elevated to near critical fire weather conditions expected across most of central and southern Wyoming this afternoon. - Showers will be more limited to western and northern Wyoming today. Light mountain snow is expected through this evening, likely reaching the western valley floors overnight. - Unsettled and cooler than normal conditions continue through the end of the week. && .DISCUSSION... Issued at 436 AM MDT Tue Apr 30 2024 There are a few showers scattered around eastern portions of the area early this morning as yesterday`s wave departs. This activity will mostly wane near sunrise, though Johnson County may see lingering showers through mid-morning. Upper flow will become more westerly today as a broad, fairly diffuse trough swings to our north. This will keep isolated convection limited to northern and western Wyoming through the afternoon. There is not much moisture to work with, though, and the majority of the area will remain cooler and dry. It will also be another windy day as an upper level jet and tightening west to east surface pressure gradient lead to widespread gusts of 25 to 35 mph. Additionally, the wind will help/combine with relative humidity dropping into the teens this afternoon to create near-critical fire weather conditions across the basins. Cyclonic flow increases this evening as the trough to our north becomes more organized and ejects a wave toward Wyoming. This will help advect in a little more Pacific moisture, leading to additional showers for the overnight hours. This will be most widespread across western Wyoming, where snow levels will drop to the valley floors as reinforcing cooler air arrives. Accordingly, light accumulating snow is possible across Jackson Hole and Star Valley; the latest HREF run suggests a 40 to 50 percent chance of at least a quarter inch overnight. On Wednesday flow becomes southwesterly as the trough axis begins to push into the area. Precipitation will become more widespread, though still focused the most on western Wyoming. Additional light snow will make it to the western valleys through the day, though warming temperatures above freezing should limit most impacts. Otherwise, it will be another windy day, especially along the Wind Corridor; elevated to near-critical fire weather conditions will return across most of central and southern areas for the afternoon. Temperatures will cool further Wednesday night, with 700mb temperatures reaching around -8C by Thursday morning behind the trough passage. This will bring snow levels down to the basin floors; we can`t rule out some light accumulation across lower elevations east of the Divide Wednesday night through Thursday morning. However, drier air will be moving in at the same time, limiting available moisture and keeping QPF light. In fact, much of the area will likely stay dry. Unsettled conditions and cooler than normal temperatures appear likely to continue through the end of the week. The forecast reflects a messy upper flow pattern, with precipitation chances spread across the entire area Thursday and Friday. Light snow chances will continue as well, possibly down to the basins again during the overnight hours. Further out, guidance currently favors a warmer and drier weekend as transitory ridging moves in ahead of the next system. && .AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 532 AM MDT Tue Apr 30 2024 Jet energy remains overhead Tuesday with widespread westerly winds gusting 20 to 30 kts through about 02Z/Wednesday. The next shortwave arrives in northwest Wyoming late in the period. KJAC ceilings fall to BKN040-060 and showers develop over the northwest after 01Z Wednesday. Hi-res models indicate a period of steadier -SN between 04Z and 09Z Wednesday night, however, have only included -SHSN in the TAF for now due to low confidence in steady precipitation. If the steadier period of precipitation does occur, expect to see vsby reductions to IFR levels at times for KJAC terminal. Across other terminals only increasing high clouds through the afternoon and evening ahead of the next shortwave. Mountain tops frequently obscured over northwest Wyoming after 00Z and especially after 04Z. 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...Myers AVIATION...Hensley