965 FXUS65 KRIW 080512 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1111 PM MDT Thu Oct 7 2021 .SHORT TERM...(This evening through Friday night) Issued at 153 PM MDT Thu Oct 7 2021 A deep longwave trough sitting off the West Coast will continue to direct moisture and several smaller weather systems through the region over the next 48 hours. The first of these smaller systems is forecast to push through the western half of the state this afternoon and evening. Partial clearing ahead of this wave combined with fairly high PWs in the 0.5 to 0.6 range will lead to modest CAPE in the 250 to 500 J/kg range. SPC forecasts a Marginal Risk for severe thunderstorms, with isolated storms containing strong gusty outflow winds or large hail. This seems reasonable given the aforementioned parameters, and have added scattered thunderstorm wording to the forecast. Several thunderstorms can be seen forming currently. Gusty outflow winds are likely to be the most widespread impact from these storms, but any hunters or hikers in the mountains will also want to keep a eye (and ear) out for lightning, and take appropriate measures if a storm is headed toward your vicinity. Temperatures today will remain similar to those seen Wednesday. Those who like warmth should take advantage of today's and Friday's temperatures which are 5 to 10 degrees above seasonal normals, despite the abundant cloud cover. The weekend into early next week will not be so mild. Another shortwave is aided by favorable jet dynamics overnight into Friday, with widespread rain showers expected over the mountainous regions of western Wyoming. A few tenths of an inch of rainfall is likely for the National Parks and far western valleys. This rainfall pushes into Montana after sunrise Saturday, bringing a brief reprieve from showers. The main trough moves overhead by the afternoon hours, and all basins across western and central Wyoming see chances for rain increase notably Friday evening into the overnight. Rain will not be constant for most areas, but unlike in past systems, even valley and basin locations are likely to pick up wetting rains at some point between Friday afternoon and Saturday evening. .LONG TERM...(Saturday through Thursday) Issued at 153 PM MDT Thu Oct 7 2021 Broad positively titled trough will continue slowly moving over the forecast area Saturday morning, with precipitation ongoing from SW Wyoming toward north-central WY. As the day progresses the area of precipitation will move southeast and temperatures will gradually decrease in the mid-levels, increasing the possibility for snow in the mountains. The surface low is also expected to move eastward from eastern WY, aiding in pressure rises and increase northerly flow east of the divide, and west-northwest flow west of the divide. Models are currently showing the highest precipitation occurring over the northwest mountains as well as the Bighorn Mountains and northern Johnson County. Showers will linger Saturday night until weak ridging moves over the area early Sunday morning. Clouds will increase over northwest WY Sunday though as zonal flow begins to push moisture in the high and mid-levels over the northern Rockies. The expected strong trough starts digging onto the west coast late Sunday, bringing showers to northwest WY early Monday morning. While the GFS and ECMWF continue to show both similarities and differences, it appears that a cold front will push through the area late Monday, bringing strong north-northwest flow to much of the area as well as widespread precipitation. Starting out as rain, snow should quickly follow at even the lower elevations with 700mb temps dropping below -6C over much of the area. The mountains should see several inches of snow with lower elevation light accumulations. North winds will be strong on Tuesday with gusts over 35 mph east of the divide and into eastern Sweetwater County. Precipitation should move out of the area Tuesday night with temperatures dropping below freezing across the entire area. Some model solutions are not as progressive and keep precipitation over the area into Wednesday morning though. && .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... Issued AT 153 PM MDT Thu Oct 7 2021 Wildfire weather concerns decrease dramatically over the next week as temperatures cool and continued moisture streaming in from the southwest brings multiple chances for wetting rains/snow to the region. Minimum RHs over the next week remain quite high, rarely falling below 30 to 40 percent. Scattered to widespread showers are likely today through Saturday, and then snow levels drop down to valley/basin floors with a big winter weather system looking more and more likely next Monday through Wednesday. Prescription burners will have a hard time finding a high confidence multi-day dry window over the next week, but there are some hints that next Thursday through Saturday could be mostly dry; however, this is still a low confidence period, given it is 7 to 9 days out. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...VandenBoogart LONG TERM...McDonald AVIATION...CNJ FIRE WEATHER...VandenBoogart