Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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597 FXUS65 KRIW 250852 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 252 AM MDT Sat May 25 2024 .KEY MESSAGES... - An unsettled start to the holiday weekend with scattered showers and isolated thunderstorms spreading from southwest to northeast. - Conditions improve after that, with showers restricted to the north and east Sunday. - After a dry and pleasant Memorial Day, unsettled weather returns for midweek. Details on timing of precipitation this far out remains uncertain. && .DISCUSSION... Issued at 250 AM MDT Sat May 25 2024 Long time residents of western and central Wyoming know that Memorial Day weekend is known for being rather unsettled and wet, and at times cold with snow. And, portions of this weekend will be no exception. But there is not all bad news. The good news is that all areas will have at least one nice and dry day, and many areas will have two. The bad news is most of areas will have all three remain dry. Satellite imagery is showing some moisture moving into the area as I write this around 2 am. The chance of showers and thunderstorms today looks to progress from southwest to northeast, with areas with like Buffalo and Casper seeing it last. As for the strength of storms, there is some CAPE (Up to 500 J/Lg). However, lifted indices only top out around minus 2 and there is not a ton of jet support. Clouds spreading over the area will also limit instability somewhat. For today, it looks the western and southern portions of the area will see the most showers and storms today (topping out at around a 3 in 4 chance) with tapering chances further east (dropping to less than a 1 in 5 chance). Many area East of the Divide may be dry most of the day. With the cloud cover, temperatures will average slightly below normal. And yes, in the mountains above 8000 to 8500 feet, there will probably be some snow, but amounts should remain light for the most part. The Pacific system bringing the showers will move across the state tonight, and the chance of showers will shift more northeastward, with southern Wyoming drying out. A trailing shortwave will then brush by northeastern portions of the area. This wave has little moisture to work with, but does have better upper level support with a 90 knot jet moving into northern Wyoming. This will bring another chance of showers and thunderstorms across roughly the northeastern third of the area, roughly north of a Jackson to Thermopolis to Casper line. Areas further south will likely have a dry day. There will be enough downward momentum from the right front quadrant of the jet to bring a gusty breeze, the central Wyoming, but nothing close to high wind is expected. As for chances of showers, they range from around 2 out of 5 around Buffalo then lessening southwestward, with higher POPS in the mountains. These showers should end fairly quickly Sunday evening. Monday definitely looks like the nicest day of the holiday weekend as ridging moves over Wyoming and brings a day of sunshine and near normal temperatures. Uncertainty then increases from later Tuesday through much of the week. The ridge then shifts east as another upper level low moves onshore in the Pacific Northwest and moves eastward. Guidance remains divided on the timing of the shortwaves and how far south impacts can set in this area. Odds definitely favor northern Wyoming at this time. But details on timing of the waves and how far south showers can get remains in flux. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 949 PM MDT Fri May 24 2024 Prevailing VFR conditions through about the first half of the period. Two rounds of showers move through the area over the next 24 hours. The first occurs at the start of the period, with most likely impacts at KRKS through about 15Z. Models have shifted the best precipitation chances southward, so KRKS could see very little precipitation. Have kept prevailing rain in the TAF for now, but confidence is lower. KCPR has about a 10% chance to see a shower. The next round comes Saturday late afternoon through the evening. Showers and thunderstorms are possible with this push of moisture. High-resolution models have a slightly better grasp on starting times, but struggle with the speed of the system and how long precipitation chances linger into the evening and early night. Have attempted to put average start and end times in the TAFs but would not be surprised to see timings adjust a few hours in either direction for future issuances. 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...Hattings AVIATION...Wittmann