Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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568 FXUS65 KRIW 242157 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 357 PM MDT Fri May 24 2024 .KEY MESSAGES... - Dry through the end of the day. - Unsettled conditions return this evening with showers moving into southern Wyoming. - Widespread showers and thunderstorms expected Saturday. - Sunday will see lingering showers east of the Divide. - Warmer and drier Memorial Day through the middle of next week. && .DISCUSSION... Issued at 156 PM MDT Fri May 24 2024 Transitory ridging has taken over in the wake of yesterday`s system. This has led to a warmer and drier day across the area, though highs will still peak about five degrees below normal for this time of year. Returning southwest flow near the surface will make for a breezy afternoon for most locations while mixing down drier air that has moved in aloft. This will lead to a few hours of slightly elevated fire weather conditions for portions of central and southern areas where humidity will drop below 20 percent. The quiet weather will be short-lived as unsettled conditions return this evening. Pacific moisture will increase with the arrival of a shortwave within the southwest flow. This should lead to some light showers overnight, mainly limited to the southern half of the area. This first wave will be quickly followed by a stronger shortwave trough that will move into western Wyoming by late morning. This will bring a reinforcing shot of moisture that will contribute to fairly widespread convection. Showers and thunderstorms will move from west to east through the afternoon. Hi-resolution models have been keying in on southern portions of the CWA for the best parameters for a few stronger storms by mid-afternoon (CAPE over 500 J/kg and bulk shear 30-45 knots). There is some uncertainty on how quickly clouds can clear from the first wave there which could limit instability later on. Otherwise, this system is not very cold, and high temperatures won`t be too much different than today. Snow will be limited to the mountains with only light accumulations. The entire area has a good chance (~60 percent) of at least a little rain, with the most accumulation along and west of the Divide (40-60 percent chance of a quarter inch or more). Showers will mostly come to an end Saturday evening save for some lingering activity across northern Wyoming into Sunday morning due to another quick shortwave clipping the area. Sunday continues to trend drier for most locations with Saturday`s wave moving off to the east. The exception will still be across northern Wyoming, and especially the Bighorns and the Powder River Basin. These areas will see another weak wave dipping down from Montana, as well as a better moisture pool for an additional round of showers in the afternoon. Memorial Day will be dry as stronger ridging returns to the area. Temperatures will return to around or a few degrees above normal. Further out, ensemble guidance still favors ridging to persist through midweek before weakening by the weekend. This would keep drier conditions and temperatures around or above normal through much of next week. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 356 PM MDT Fri May 24 2024 Relatively quiet weather expected through the first 12 hours of the forecast period. Westerly winds gusting 20 to 25kts will continue to diminish toward sunset. Otherwise, VFR conditions prevail at all terminals with only FEW to SCT mid- and high-clouds through the evening hours. Cloud cover begins to increase later this evening, especially west of the Divide as the next shortwave pushes into the region. Models indicate two separate waves of moisture with this system. The first, looks to impact KRKS overnight, between 09Z and 14Z Saturday. Have kept VFR for now, but occasional MVFR conditions are certainly possible (30% chance) during heavier showers. With the second wave, hi-res models are struggling to resolve exact timing, so have included PROB30 groups for most terminals to highlight best chances of precip and associated MVFR or near MVFR conditions. 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