588 FXUS65 KRIW 080943 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 343 AM MDT Fri Oct 8 2021 .SHORT TERM...Today through Saturday The active weather will continue through the short term. Showers are ongoing this morning across portions of the area as a wave moves across the area. Some lightning is lingering as well although this has decreased over the past few hours. The heaviest of this wave should move away by sunrise with a lull for a few hours this morning. However, another, more potent system will begin to move into the west later this morning and then press across the area this afternoon and tonight. Like the previous system, the main impacts will be in the west today with dry weather possible East of the Divide for much of the day. There could be a decent amount of QPF with this system as well. Cooler air will move in behind the associated front and drop snow levels tonight, possibly down to around 8000 feet by late Friday night. We thought about a winter weather advisory for portions of the western mountains. However, the bulk of the moisture will have moved out before the much cooler air arrives. In addition, with the warm ground temperatures, impacts on roads will be minimal unless the snow is really heavy. The advisory level amounts would be restricted to the higher elevations above pass level and in more remote areas. We will issue a Special Weather Statement to cover for this. The day crew could take another look at this if they want to. Showers and embedded thunderstorms will then spread across the entire area tonight as the cold front sweeps through and gets some extra lift from the left front quadrant of an 150 knot jet streak passing across northern Colorado. The main threat from any thunderstorm would be heavy rain. Small hail will also be possible given the low wet bulb zero levels. The chance of storms may linger through the night. Saturday looks unsettled and cooler as wrap around moisture moves into the area. Again, all areas will have a chance of showers with some snow in the mountains. We lingered the chance of thunder as well, although with a lot of cloud cover we kept the possibility as isolated. Showers should really begin to end toward sunset as the system departs stage east. Something very interesting may be brewing early next week though. My partner will have more on that in the long term discussion. .LONG TERM...Saturday night through Thursday Rain and snow from Saturday's system will mostly end by midnight Sunday, but still could see some lingering showers overnight. Sunday will see a brief reprieve from activity as a transitory ridge moves across the area. The sun should return, with afternoon highs increasing by at least a few degrees. Then, a strong trough begins to move into northwestern Wyoming Sunday evening. This is still looking like the first widespread, significant snowstorm of the season. Timing seems to be in reasonable agreement, with precipitation starting out as a rain and snow mix across northwest Wyoming by early Monday, spreading southeast throughout the day. Rain in the lower elevations will change to snow Monday night as a strong cold front sweeps through from the north. Snow will continue across the area through Tuesday as the trough axis slides across the state, with a strong north to northeast wind across most of the area. The main disagreement in model solutions continues to be whether the system moves out quicker (GFS) or if it lingers, keeping precipitation wrapping around the low through Wednesday (ECMWF & Canadian). Have played the middle ground in the grids, keeping decent PoPs through the first half of Wednesday. Nonetheless, all locations have a good chance of snow with this system. && .AVIATION...06Z Issuance West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals Shortwave energy approaching southwest Wyoming late Thursday evening as earlier showers and storms decrease in coverage and intensity. VFR conditions will deteriorate to MVFR between 06Z-12Z/Friday at all but KRKS as this wave and associated moisture track northeast. These conditions are likely to continue until around midday Friday when precipitation wanes, low-level mixing increases, and ceilings rise to VFR. However, this reprieve will be short-lived as another shortwave arrives for the afternoon and widespread MVFR returns through at least Friday evening. KRKS to be VFR throughout with the best chance for convection coming Friday afternoon. Mountain tops are likely to be obscured through the period. East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals All terminals to be VFR through 00Z/Saturday. Isolated ongoing showers will continue to track northeast and dissipate overnight. Another wave of moisture aided by a shortwave and left exit region jet dynamics arrives around midday with convection breaking out during the afternoon. Showers and isolated thunderstorms will be most common between about 22Z/Friday and 04Z/Saturday. Mountain tops along the Continental Divide are likely to be obscured through the forecast period. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on smoke, icing, and turbulence forecasts. && .FIRE WEATHER... A weather system will move across the area today and tonight. Showers and isolated thunderstorms will be possible across the west at anytime today and tonight. East of the Divide, any showers should end early with most of the day dry. The best chance of showers here will be late today into tonight. Cooler air will move in behind the system with snow likely in the higher elevations. Relative humidity will remain above critical levels. A gusty breeze will develop at times in the afternoon. Further showers are likely on Saturday as well. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...Hattings LONG TERM...Myers AVIATION...Jones FIRE WEATHER...Hattings