516 FXUS65 KRIW 272034 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 134 PM MST Thu Dec 27 2018 .SHORT TERM...This evening through Friday The forecast area remains split between two flow regimes; south- southeasterly flow over western and central portions from the storm system over the Great Basin and northerly flow over eastern portions from the occluded part of the major storm currently over the Plains. Snow remains isolated and light this afternoon, with patches of very low clouds. The best chances for snow will be over areas west of the Divide (minus much of Sweetwater County). By this evening, this will transition to central portions. North- northeast winds from the sfc-700mb will aid in this development, with gradually decreasing chances by 12Z Friday. The southern end of the Wind River Mountains over to the Green Mountains will have the best chances through the overnight hours, before the snow finally ends by sunrise Friday morning. However, snowfall amounts will remain light across the forecast area. Most areas will stay in the 0.5" to 1" range, with up to 2" in the western and central mountains. Locally higher amounts of 3-4" are possible near Sinks Canyon/Red Canyon/South Pass. Conditions will be dry Friday, as skies gradually become partly cloudy by the afternoon. Temperatures will continue to be frigid tonight and Friday. Breaks in the clouds allowed temperatures to drop into the negative teens in a few places last night. This is not expected to occur tonight, as mostly cloudy/overcast skies are expected. .LONG TERM...Friday night through Thursday Weak high pressure will continue Friday night into Saturday morning for mostly clear skies. Another weak weather system will start moving into northwest WY by Saturday morning, increasing clouds across western WY and increasing southwest winds from southwest into central Wyoming by midday. Light snow showers should start in the northwest mountains by sunset Saturday. A stronger pocket of energy will move from the Pacific Northwest into eastern Idaho Saturday night into Sunday morning, increasing moisture and cloudiness and serving to strengthen south to southwest wind across the southern parts of the state. Precipitation will increase over all of western Wyoming around sunrise Sunday. The latest models runs are showing a front move through the area during the day on Sunday and spread moderate winds with snowfall through most of the area. At this time, looks like 3-6 inches possible in many lower elevation areas, with 6-12 inches in the mountains. Gusty northwest winds will follow the front Sunday afternoon and precipitation will become heavier over the eastern half of the state. Looking for heavy snowfall for a couple of hours from Johnson into Natrona counties with north wind late Sunday afternoon. This weather system is likely to cause hazardous travel conditions over some of the area. Light snow showers with very cold air and north wind will continue Sunday night into Monday. All of western and central Wyoming will be below normal for temperatures through Tuesday. For the first couple days of the new year, the upper level flow will remain north to northwesterly to continue the cold temperatures. Tuesday will see some clearing of the skies, with clouds and light snow showers returning Tuesday night into Wednesday morning. From Wednesday into Thursday, upper-level high pressure will build into the area, bringing more bright blue skies. Inversions are likely to strengthen though and keep temperatures very cold. Some of the higher elevations may actually see warming though. && .AVIATION...For the 00Z TAFS through 00Z Friday East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminal MVFR conditions will be widespread tonight, as areas of -SN continue. KLND will have the longest period of -SN, gradually ending by 12Z Fri. LIFR conditions could return to KCPR by 12Z Fri, but will mostly likely be low MVFR through 16Z. Most terminal sites will remain to have OVC skies through 18Z Fri, as VFR conditions return. West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals MVFR ceilings, with -SN/VCSH, will continue into this evening. -SN will end across much of the area by 06Z, however, MVFR ceilings will continue. VFR conditions are expected by 12Z Fri, as skies begin to clear out. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Light snow will become more focused over central portions tonight. Accumulations amounts will remain in the 0.5 to 1 inch range for most areas, with locally higher amounts possible near South Pass/red Canyon. Conditions will be dry for Friday. Winds will be light to moderate tonight into Friday, with a northerly component. Smoke dispersal will remain poor through the next few days. Winds will increase from Saturday onward. && .RIW WATCHES/WARNINGS/ADVISORIES...NONE. && $$ SHORT TERM...LaVoie LONG TERM...McDonald AVIATION...LaVoie FIRE WEATHER...LaVoie