FXUS65 KRIW 241737 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1137 AM MDT Fri Oct 24 2025 .KEY MESSAGES... - Mostly sunny and light winds today, with temperatures 5 to 15 degrees above normal. No precipitation expected. - The next weather system brings widespread gusty southwest winds over 30 mph starting Saturday afternoon, continuing through Monday. Most widespread gusty winds occur Sunday. - Western mountain snow occurs Saturday night through early Tuesday morning. Expect winter travel conditions over mountain passes from moderate to heavy snowfall and gusty winds. && .DISCUSSION... Issued at 146 AM MDT Fri Oct 24 2025 Yesterday was a pleasant autumn day across the area. If that's your type of weather, then you're in luck, because today is much the same (and if it's not, stay tuned). As the upper low to our south moves away from the area, clouds lessen for today, with a mostly sunny sky, relatively light winds, and mild high temperatures around 60 degrees. The interesting part of the forecast starts Saturday afternoon. A longwave trough will begin moving into the area early Saturday. This tightens the pressure gradient, with southwest wind gusts 20 to 30 mph being common over the area. Favored locations, like the Wind Corridor from South Pass to Casper, see stronger winds. As the trough approaches in the afternoon, stronger winds also look favorable for the western mountains, including Yellowstone; gusts over 30 mph likely, with areas over 40 mph. The bulk of this system occurs Saturday night through Monday night. The main aspects to it will be wind and mountain snow. Starting with wind, like Saturday, gusty southwest winds occur across the area, 30 to 50 mph. It should be noted that most winds will have continued from Saturday afternoon into Sunday afternoon, with no lessening winds overnight. Gusty winds will lessen a bit for some locations Sunday night, but overall, winds continue through the day Monday. The other weather element is snow. Quick note, that outside the following discussed snow, there will be continuous rain chances (30% to 50%) for the lower elevations. Latest snow totals are similar to what was seen yesterday, so there is now some consistency, which adds confidence to the current snow amount forecast. Highest totals are for the Teton, Salt/Wyoming, Gros Ventre, and far western Absaroka Ranges, with notable amounts also over the higher elevations of the Wind River Range and across the southern half of Yellowstone. Forecasted, deterministic mean amounts are 9 to 12 inches for these mentioned locations. The NBM spread (a 25th to 75th percentile difference) is around 6 inches, so about 3 inch buffer to those given mean amounts. Notably, there is a greater spread across Yellowstone, likely due to model differing in storm track (positioning of the jet stream and favored dynamics late Sunday into early Monday). The spread there is 8 inches, so plus or minus 4 inches on the current deterministic forecast. In any case, it is likely (75%) that winter highlights will be needed for the mountains. Will hold off for now due to lacking confidence in potential amounts and will hope that consistency remains with later runs today. EFI/SOT (a tool to look at potential for high-end events) still has snow amounts in the 50th to 70th percentile, with SOT slightly highlighting the Tetons/southern Yellowstone, again alluding to the greater uncertainly there, but potential for higher- end amounts. The overall takeaway is that there will be winter weather over the western mountains Saturday night through Monday night. Expect winter travel conditions, with moderate to heavy snow possible and gusty winds bringing blowing snow and reduced visibilities. Notable passes include Teton, Togwotee, and Salt River. Conditions improve late Monday night into Tuesday morning as snow lessens. Light snow lingers through Tuesday morning. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1137 AM MDT Fri Oct 24 2025 VFR conditions and generally light winds will continue at terminals through tonight. A scattered cloud deck will begin moving into Wyoming from west to east around 12Z Saturday as a system approaches. An associated strengthening pressure gradient will help to increase southwest winds at KCPR by 14Z with gusts to around 25 knots. Wind is then expected to increase at most remaining terminals after 18Z in the next forecast period. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on smoke, icing, and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION...Wittmann AVIATION...Myers