Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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544 FXUS65 KRIW 291119 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 519 AM MDT Mon Apr 29 2024 .KEY MESSAGES... - Another afternoon of isolated showers and thunderstorms, spreading east with a cold front this evening. Gusty wind ahead of this front. - Light accumulating mountain snow is expected through this evening. Snow levels will approach the floors of western valleys, but any accumulation will be minor. - Elevated fire weather conditions Tuesday for much of central and southern Wyoming. - Unsettled conditions continue midweek, with chances for light snow for most of the area Wednesday night. && .DISCUSSION... Issued at 440 AM MDT Mon Apr 29 2024 A few light showers are lingering early this morning in the wake of yesterday`s wave. These will mostly die off as we near sunrise, leaving a dry rest of the morning. However, the next shortwave within the broadly cyclonic flow is quickly approaching. With the addition of some Pacific moisture advection, this wave will kick off another round of isolated convection this afternoon across western Wyoming. The bulk of this activity will stay west of the Divide through the afternoon, before increasing in coverage to the east this evening as a cold front pushes through. Ahead of this front, wind will increase as a surface low develops across northeastern Wyoming. This will make for a gusty afternoon for the majority of the area, but especially from southwestern Wyoming through Natrona County. Also to note will be a few inches of snow across the mountains through this evening. As the cold front passes, snow levels will drop, possibly down to the floor of Jackson Hole after sunset. This valley could see a brief period of light snow, but precipitation will be waning as temperatures drop. Regardless, the latest run of the HREF suggests a 30 to 50 percent chance of light accumulation (0.1") for the lower elevations of Jackson Hole. While a few snow showers may linger across the mountains, precipitation elsewhere will come to an end overnight as the front moves from west to east. On Tuesday a flattened, diffuse trough will be situated to the north of Wyoming. Flow will be more westerly across the area. Convection chances will return, but will be more restricted to northern Wyoming. Most of the area will be cooler and dry, though again with a gusty wind through the afternoon. With drier air aloft and a mixing wind, humidity values are likely to fall into the teens across most of the lower elevations leading to elevated fire weather conditions. On Wednesday, the northern trough axis is progged to rotate towards Wyoming. This will return wider precipitation coverage to the area, again especially across northern and western Wyoming. Cooler temperatures are set to arrive Wednesday night, likely bringing snow levels down to or near basin floors by Thursday morning. Models are coming more into agreement on this, showing 700mb temperatures down to -8C. However, this system does not look to have much moisture to work with, and any accumulations currently appear light. Uncertainty creeps back up further out. Guidance currently favors a warmer end to the week, though with lingering precipitation chances as unsettled conditions continue. && .AVIATION /12Z TAFS THROUGH 12Z TUESDAY/... Issued at 516 AM MDT Mon Apr 29 2024 VFR conditions prevail through the morning. Winds begin to increase this morning, with gusts to around 30 knots by the afternoon for many sites. There is a possibility for higher gusts associated with virga showers and thunderstorm outflows. Best likelihood for stronger gusts up to 35 to 40kts will be at KBPI, KCPR, KPNA, and KRKS between 22Z and 04Z. Precipitation begins over western Wyoming around 18Z. As a weak cold front passes through, rain chances spread eastward through the day, reaching the Continental Divide roughly around 00Z. All sites have a chance of rain through the TAF period, but lower confidence for locations east of the Divide, so have left mention out for most locations for now. KBPI and KPNA also have a less than 30% chance for rain showers this afternoon, so have also omitted mention of showers for those sites. There could be an isolated thunderstorm late this afternoon, with highest chance (30%) at KJAC between 21Z and 00Z. Otherwise, have left TS mentions out of all terminals. Other terminals with a chance of TS include KCOD, KCPR, and KRKS, but chance is low enough (less than 20%) not to mention in the TAFs. 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/Wittmann