Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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745 FXUS65 KRIW 220354 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 954 PM MDT Tue May 21 2024 .KEY MESSAGES... - Showers and isolated thunderstorms continue this afternoon and evening. The majority of precipitation likely remains east of the Divide. - Clearing skies will cause temperatures to drop into the mid 30s overnight, but light winds should prevent widespread freezing, so the Freeze Watch has been canceled. - Another round of widespread showers and high elevation snow for the second half of the week. - Near to below freezing temperatures are possible for Friday morning. && .DISCUSSION... Issued at 158 PM MDT Tue May 21 2024 Only 4-5 days ago temperatures were in the mid to upper 70s and it was feeling like summer was on its way. Unfortunately, the rollercoaster that is Spring weather in WY continues, with winter making a return to parts of the Cowboy State this morning. Parts of Lander and Casper saw a brief period in which rain transitioned over to snow this morning. These areas have now returned to rain, as the strong May sun has warmed daytime temperatures. Snow is continuing to fall across high elevation mountain ranges, such as the Bighorns. The upper-level low that developed overnight and moved into the Northern Plains will continue to bring chilly and unsettled weather for today. Periodic showers will be possible throughout the day as moisture from this disturbance wraps back around from the north. The bulk of the precipitation will remain east of the Divide with a (40- 80%) chance of showers during the afternoon and evening. Precipitation chances west of the Divide are less likely, with a (10- 40%) chance of a shower this afternoon and evening. A few isolated thunderstorms are possible this afternoon/evening with much of the state seeing about a 20% chance. The amount of sun that can peak through the low clouds east of the Divide will be key to determining if enough instability can develop to fuel thunderstorm development. Overall, the threat for thunderstorms remains low, with the only concern being gusty outflow winds from any that do form. Highs across the Cowboy State today will be chilly with temperatures in the upper 40s to low 50s. These temperatures are nearly 15 to 20 degrees below normal values for this time of the year. This leads to concerning temperatures overnight into Wednesday morning. Tonight skies are expected to gradually clear out. This all points to efficient diurnal cooling occurring, with lows dropping into the 30s for basins. Light breezes should mitigate frost concerns, and the Freeze Watch has been canceled. That being said, overnight lows will be below seasonal normals, so those not wanting to risk frost may want to take appropriate actions. Wednesday sees a quick moving and weak transitory ridge move through the region. Behind this ridge is another shortwave that is barreling its way south from British Columbia. Due to the Canadian origin of this system, chilly temperatures return to the Cowboy State. Precipitation looks to remain mainly across the northern and western half of the CWA. These areas have a (40-80%) chance of precipitation starting Wednesday afternoon into Thursday afternoon. The remainder of the state may see a few showers but at a much lower likelihood, with models showing a (10-30%) chance for precipitation. High elevation mountain ranges across the northern half of the CWA may see another round of snow with amounts nearing Advisory criteria. By Thursday evening, precipitation will begin to wind down as the shortwave moves out of the region. Depending on how quickly the skies can clear, we may have another chilly morning come Friday. Currently models are showing a (20-50%) chance of lows at or below freezing. If this trend continues there may be another round of Freeze Watches issued for low elevation basins. The upcoming holiday weekend will be worth monitoring as models are indicating a potent low moving through the region sometime during the weekend. This may lead to some widespread unsettled weather across the Cowboy State. However, conditions look to improve by Monday with temperatures returning to near normal values. There still is a lot of uncertainty regarding the forecast this far out in advance, so its very possible things may change as we near the weekend. && .AVIATION /06Z TAFS THROUGH 06Z THURSDAY/... Issued at 953 PM MDT Tue May 21 2024 West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals One weather system exits tonight as another moves in tomorrow. Prevailing VFR conditions will continue tonight before the next system moves into the area. Then, rain showers will move into western Wyoming late Wednesday morning. This will impact KJAC, but conditions will predominantly remain VFR even as showers pass through. Steadier rain is possible (60%) at KJAC Wednesday evening after 01Z, so reductions in vis to MVFR are possible (40%). Isolated thunderstorms will develop Wednesday afternoon into Wednesday evening, mainly in the mountains around KJAC. Not enough confidence in thunderstorm coverage for VCTS at KJAC at this time. Other terminals will remain dry, although there is a 20-30% chance of rain at KBPI/KPNA Wednesday evening. Wind will increase at all terminals late Wednesday morning from the southwest, with gusts of 20-30 knots at all terminals through the afternoon hours. A wind shift from the northwest will occur late Wednesday evening. Mountaintop obscuration will begin around KJAC late Wednesday morning and continue through the TAF period. East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals One weather system exits tonight as another moves in tomorrow. Prevailing VFR conditions will persist over the next 24 hours, but wind will increase for all terminals late Wednesday morning. Wind will be southwesterly sustained in the teens, gusting 20-30 knots from late Wednesday morning through Wednesday afternoon. A shift to northwesterly wind is likely (70%) Wednesday evening for KWRL/KRIW/KLND. 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...Dziewaltowski AVIATION...Rowe