KRIW issues Area Forecast Discussion (AFD) valid 2019-11-28T17:48:00Z 118 FXUS65 KRIW 281748 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1048 AM MST Thu Nov 28 2019 .SHORT TERM...Today through Saturday ...Snow to increase during the Thanksgiving Holiday Weekend... Light snow continues to stream northward along the ID/WY border this morning. The flow aloft is turning more S-N vs SW-NE, as the upper low over CA continues to dig. Snowfall amounts today will be slightly higher than forecasted yesterday, with 2 to 3 inches expected in the lower elevations, from southern Lincoln County to Hoback Junction and the Jackson and Star Valleys. Snowfall amounts in the mountains and portions of Yellowstone will range between 3 and 6 inches. Will reissue the Special Weather Statement for these far western zones. Otherwise, temperatures will remain cold for much of the area today. Gusty S winds will raise temperatures into the upper 30s to near 40 degrees over portions of Sweetwater County to the Continental Divide. Conditions will begin to deteriorate over SW portions this evening, as the first of a series of shortwaves/fronts begin to move over the area. An area of light to moderate snow will move over W Sweetwater and S Lincoln counties this evening, moving N into Sublette County. As this snow moves into Sublette County and the Upper Green River Basin, this will mark the beginning of the storm system to impact this area. Another shortwave associated with an occluded front will then make its way over SW WY by 12Z Friday, bringing snow across far W portions through the rest of the morning as it moves N. By 12Z Friday, a surface low will form along the cold front over far SW WY. The occluded low will be over NE NV. This will keep the focus of the snowfall over areas W of the Divide through the morning Friday. By 18Z, the cold front will continue to progress E into CO. A new surface low will begin to develop, with leeside cyclogenesis forming this low along the CO Front Range by 00Z Saturday. Snow will spread on the E side of the Divide after sunrise Friday morning, becoming widespread over the central basins by the afternoon. A new occluded front will be in place over S-central WY by 00Z Saturday. This will be the main lifting mechanism for the snow E of the Divide Friday night into Saturday. Gusty W to NW winds will then occur during this time behind the cold front. W winds with gusts up to 25 mph will occur over Sweetwater and S Lincoln counties by sunset Friday evening. This will create difficult travel conditions across Interstate 80. Thankfully, snowfall amounts are expected to be very light with 2 to 3 inches. NW winds 20 to 25 with gusts up to 35 mph will occur over N portions of Johnson County and the Bighorn Basin Friday night as well. Near- blizzard conditions will occur over these areas during this time. N Johnson County will be the most likely to have blizzard conditions, as this area is prone to NW winds. The pressure gradient will be tight over E WY by 12Z Saturday, as the surface low deepens to at least 988mb. These conditions could extend to Natrona County, if current model trends have this low deepening even further. The storm track will also play a role in this as well. Overall, 3 to 6 inches of snow is expected across much of the area with locally higher amounts up to 8 inches east of the Divide. 6 to 12 inches will fall in the mountains, with the W mountains getting 7 to 14 inches. .LONG TERM...Saturday night through Wednesday A weak ridge will build over the area in the wake of the winter storm Saturday night. This will keep most of the forecast area dry through Monday. Late Sunday night, a minor wave will bring in some moisture to far western Wyoming. Light snow will fall across the west through Monday, with chances lasting into Tuesday as well. This will include the Tetons and Jackson Valley, but not expecting significant impacts with this system. Beginning Monday, the afternoon temperatures will show a slight warm up, with some locations reaching highs near 40. There will be gusty winds throughout the period, mainly from South Pass to Natrona County and across the eastern Absarokas. && .AVIATION...(For the 18Z TAFS through 18Z Friday afternoon) Issued at 1047 AM MST Thu Nov 28 2019 West of the Continental Divide...KRKS, KJAC, KBPI, KPNA Terminal sites. Light to moderate snow falling at KJAC will decrease early this afternoon. Chance for snow at KPNA and KBPI throughout the afternoon and evening. MVFR/IFR conditions will be possible through Thursday evening with these periods of snow. Mountain obscuration is likely through the entire period. Wind shear conditions are possible at most terminals through late morning Thursday. East of the Continental Divide...KCPR, KLND, KRIW, KCOD, KWRL Terminal sites. Otherwise, mainly VFR conditions for sites until late in the period. KLND has a slight chance for some snow coming off of the Wind River Mountains, but accumulations will be low at the terminal. Clouds will lower through the evening and overnight with snow and isolated MVFR ceilings possible everywhere, except KCPR, with conditions expected to deteriorate after 12z Friday. && .FIRE WEATHER... Light snow will continue across the far west today. Temperatures will remain cold across much of the area, except over zones 279 and 289, where temperatures will rise into the upper 30s to near 40 degrees. This will be due to breezy southerly winds, mixing the cold air out of the area. A major storm system will impact the area Friday and Saturday, with areas of moderate to heavy snow possible. Strong winds will also occur Friday night into Saturday for areas east of the Divide, especially across zone 281. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Storm Watch from Friday morning through Saturday morning for WYZ003>007-017>019. Winter Storm Watch from late tonight through late Friday night for WYZ012>016-023>027. Winter Storm Watch from Friday afternoon through Saturday afternoon for WYZ008>011-020-022. && $$ SHORT TERM...LaVoie LONG TERM...Swanson AVIATION...Myers FIRE WEATHER...LaVoie