161 FXUS65 KRIW 100850 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 250 AM MDT Wed Oct 10 2018 .SHORT TERM...(Today through Friday night) A colder, faster, and more potent weather system will be impacting the CWA during the next 12 hours. The closed low appears to be spinning over the Idaho/Utah border. The mid and upper level low will be tracking east across Southern Wyoming today before rapidly transitioning into an open wave and weakening later this afternoon. Strong difluent southwest flow out ahead of this approaching system and QG forcing will enhance snowfall over Southwest and Southern Wyoming today. As a result, winter weather advisories have been issued yesterday for the snowfall today for the Salt and Wind River Range, the Upper Green River Basin, mainly for the southwest portion of that zone, Southern Lincoln County, and Sweetwater County. The Interstate 80 corridor as well as South Pass will have 40 mph wind gusts combined with heavy snowfall. Over South Pass, it should be cold enough for these winds to combine with the heavy snow to produce a period of blowing and drifting snow mainly between 10Z and 16Z this morning. The track of this storm is favorable for Lander to receive accumulating snow and went with 1 to 3 inches of snow there for this morning (upslope). Weak echoes are already seen moving east to west across the Lander Foothills. Snow has already been falling intermittently there. This weather system will rapidly move off to the east and fall apart this afternoon with snowfall decreasing. However, snowfall will increase tonight over Northwest Wyoming as isentropic lift quickly takes over ahead of the next shortwave that will track southeast within the backside of the main trough Thursday. Snow amounts across Northwest Wyoming will have low end advisory amounts tonight. Then for Thursday, expect rain and snow showers to encompass much of the western and northern half of Wyoming with the cold air aloft asct with the next troughpa. Then on Friday, a respite from the cold wet weather will take place between weather systems as a flat ridge builds into the area. Friday will be the warmest day of the week with highs in the 50s over many areas east and west of the divide. On Friday, the long wave trough in the 5 wave pattern will begin to shift east to the Midwest. Clouds will increase from the north Friday night with some light precip breaking out over the far north ahead of an approaching strong cold front. .LONG TERM...(Saturday through Wednesday) A strong Canadian cold front will plunge south across the area Saturday morning, spreading a quick shot of snow across north central zones, with longer duration snow and advisory or higher amounts possible across Fremont, Natrona and Sweetwater Counties, especially in upslope favored areas around Casper and Lander. ECMWF if further west with associated vort maxima diving south across eastern Idaho Saturday (more favorable for Lander Foothills and southwest Wyoming) while the GFS further eastward track roughly along the Continental Divide would be more favorable for Casper. A much more favorable dendritic growth profile arrives with this system with H7 temps -8c to -13c, H5 temps -23c to -28c behind the cold front on Saturday. Snow will taper off north to south Sunday morning with unseasonably cold airmass remaining over the area, with most highs across the central basins and south in the 30s. Ridge over the eastern Pacific is expected to progress onto the West Coast by Wednesday. The next clipper system diving out of central Canada on Monday is expected to take a further eastward track into the northern High Plains. Central and eastern Wyoming will receive more of a glancing blow from this system and its associated cold front late Monday and Tuesday with chances of snow showers mainly in the vicinity and east of the Bighorn Range. Upper ridge over the northwest U.S. should build into the area Wednesday and bring the start of a milder and mainly dry weather pattern through the end of the workweek. && .AVIATION...(For the 12Z TAFS through 12Z Thursday) West of the Continental Divide...(KJAC, KRKS, KBPI, KPNA) IFR to LIFR will occur at the KRKS terminal through about 18Z. Through about 10Z the IFR conditions will likely be only from low ceilings, but snow and blowing snow should develop between 10Z and 12Z and last through about 18Z. RKS terminal airfield minimums is also a good possibility. Improving conditions are expected at KRKS between 18Z and 21Z with VFR conditions possible by around 00Z Thursday. Elsewhere, MVFR conditions are expected to impact the Upper Green River Basin today with the best chance at KBPI. Periods of light snow (MVFR conditions) could begin to impact KJAC in the afternoon, and last off and on Wednesday night. East of the Continental Divide...(KCPR, KCOD, KRIW, KLND, KWRL) MVFR to IFR ceilings are likely through the morning for much of the area except for the eastern Big Horn Basin where ceilings are expected to be VFR. The best chance of snowfall will be across the Lander Foothills. Ceilings will be slow to improve this afternoon, but current forecast has most areas lifting to VFR by late afternoon into early afternoon. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts.&& .FIRE WEATHER... A cool and moist pattern will persist through at least Thursday. The next new storm system will spread another round of snow into the southwest, west, and south this morning and early afternoon. Then a separate round of snow will occur over Northwest Wyoming tonight. Scattered rain and snow showers can be expected across the western and northern half of Wyoming Thursday. Friday will be dry along with the mildest temperatures of the week with many areas on both side of the divide managing to warm up to the 50s. A strong cold front will plow south across the state Saturday delivering more snowfall to the area. Sunday will be cool and dry. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until noon MDT today for WYZ026>030. Winter Weather Advisory until 3 PM MDT this afternoon for WYZ014- 015-024. && $$ SHORT TERM...Lipson LONG TERM...Meunier AVIATION...Murrell FIRE WEATHER...Lipson