Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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856 FXUS65 KRIW 221930 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 130 PM MDT Sat Jun 22 2024 .KEY MESSAGES... - A very warm and dry west-southwest pattern expected from this afternoon through Tuesday. Temperatures will climb to the 80s and 90s Sunday through Tuesday in the lower elevations, with possibly 100 in the lower-elevations of the Bighorn Basin. - Isolated showers and thunderstorms are expected across far southern and far northern WY this afternoon. Sunday will also see isolated showers and thunderstorms over the same areas, plus the northern Wind Rivers into the SW Bighorn Basin. - Hot, dry, breezy, and gusty conditions will create elevated fire weather conditions over the next few days. - Moisture returns to western and central WY Wednesday and Thursday for increased chances of scattered showers and thunderstorms. Thursday afternoon could see some strong storms over central WY. && .DISCUSSION... Issued at 1230 PM MDT Sat Jun 22 2024 Yesterday`s storm system has moved off into the northern plains, leaving a fairly dry and stable air mass over western and central WY with moderate zonal flow in the mid-levels. Isolated thunderstorms have already initiated over the northern slopes of the Uintas late in the morning though as increased moisture remains over the central Rockies along with increasing instability to the south. This afternoon could also see some very isolated showers and storms over the WY/MT border as lingering moisture and instability over MT interacts with the west flow over the terrain. Across the middle of the state will be very warm and dry as west flow dries out the boundary layer through the afternoon and humidities drop to the 20s and teens in the lower elevations and along the east slopes of the mountains. Some areas are already seeing winds of 10-15 mph with gusts 20-30 mph, and breezy gusty winds should increase in coverage through the afternoon as temperatures climb to the 80s across the lower-elevations. Sunday will see the somewhat flattened ridge axis align north- south over WY in the morning and move eastward during the afternoon and evening. West-southwest winds should increase Sunday compared to Saturday as temperatures climb 4-8 degrees to the mid 80s to upper 90s. The lower elevations of the Bighorn Basin around Basin and Greybull have a decent shot of seeing 100 degrees - which is 12-15 degrees above normal. Once again, isolated showers and thunderstorms are possible over far southern WY as well as far northern WY. A few high-res models are indicating some storm development over the northern Wind Rivers and southern Absarokas, which then move into the SW Bighorn Basin. The hot and dry conditions Sunday will create elevated to near critical fire weather conditions, but fuels are still deemed non- critical. Caution should still be used with fires given the dryness in most areas of western and northwest WY. The same pattern continues on Monday, with similar temperatures and winds, though a weak shortwave trough should move from northern Utah through far southern WY to bring showers and thunderstorms to southwest and southern WY through the day. Temperatures remain well above normal, but should cool by 2-3 degrees over Sunday for most of the area. Amazingly, the same pattern continues on Tuesday with isolated showers and thunderstorms across southern WY during the afternoon and increased clouds along the WY/MT border. Hot and dry will persist through the center sections of the state. As a trough digs along the west coast of the US on Wednesday, the flow pattern becomes more southwesterly on Wednesday, advecting moisture from the Great Basin and Four Corners areas over Wyoming. While temperatures remain very warm, cloud cover will make a difference and help temperatures decrease a few degrees. Initial indications are for the best chances of storminess over southwest and southern WY, as well as the northwest mountains. A shortwave trough is then expected to move from WA to MT on Thursday, with a mid-level front interacting with moisture from the south. The result should be more widespread showers and thunderstorms Thursday afternoon, with another shot at severe storms, much like Friday June 21. Cooler air moves in late Thursday into Friday to bring temperatures back to normal, or even below, especially east of the divide as northerly flow drops down. Western WY on Friday should again be dry and windy. Next Saturday then appears to be mostly clear with no precipitation and light winds as high pressure starts to build again over the Great Basin. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1114 AM MDT Sat Jun 22 2024 VFR conditions will prevail through the TAF period. A light west to northwest breeze will develop at most terminals this afternoon, with gusts around 20 to 25kts. Have left the wind at KCOD as a TEMPO for now, as there is low confidence in enough mixing to develop a northwesterly wind there before the nocturnal northerly flow sets back in, so gusty winds there this afternoon will be brief if the occur at all (40% chance). Skies will remain mostly clear with possibly a few fair weather cumulus developing this afternoon across the region. This evening, winds will decrease to mostly light and variable after 03Z and skies will remain mostly clear through the night. A few terminals (KRKS and KCPR) should see west- southwest winds start to increase again late in the period (70% chance). Please see the Aviation Weather Center and/or CWSUs ZDV and ZLC for the latest information on smoke, icing, and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES...None. && $$ DISCUSSION...McDonald AVIATION...Hensley