309 FXUS65 KRIW 091758 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1158 AM MDT Tue Oct 9 2018 .SHORT TERM...(Today through Thursday night) We are experiencing the last of the dynamics with the slow moving main trough that we have been chewing on for the past few days. The main trough has traveled east to roughly the Fremont Natrona County line. There are several mid level circulations within this broad trough. One subtle circulation that appears to stand out on satl is an elongated one extending from Central Sweetwater County to far Southeast Fremont County. Other than that, there does not appear to be much in the way of dynamics attm with just mainly patchy light rain and wet snow most in places. BYG appears to have the most consistent snowfall among many other areas. This glob of precip should be the last enhanced area of precip to affect our CWA from this trough. Precip should be winding down during the next few hours. We let the winter weather advisory expire for our southern and eastern zones at midnight. Then by 12Z this morning, our attention quickly shifts to a faster, colder, more robust weather system coming out of the northwest from BC/Alberta that will dig south southeast into the backside of the long wave trough across the Pac NW to Boise this afternoon. A solid area of snowfall will move into Western Wyoming within the westerly difluent flow ahead of this next weather system today. The resultant snowfall will steadily increase in Western Wyoming during the day today. By 06Z tonight the snowfall will jump the Divide to areas to the east. More of the snow will be over the southern half of Wyoming based on the track of the low. By tonight, the low should be over SLC acdg to the GFS. In fact, this low is taking a favorable track for the Lander Foothills to get accumulating snow. With that said, the Tetons, Gros Ventre, Salts, and the Wind River Range stand to see the most snow out of this system. As for lower elevations, areas east of the divide, north of the Owl Creeks and north of Midwest in Natrona County will not fair as well. The Big Horn Basin should see rain from this. From the SLC area, the low will track to Southwest WY and open up. The Canadian and the Euro track it a little farther west over Wendover, Nevada instead of SLC by 12Z Wed. The asct h7 low is progged by the GFS to track across Sweetwater County. The best QG forcing will be found over Southern Wyoming. For these reasons, mainly the southern half of WY will see a decent quick shot of snowfall. It appears that South Pass could see a quick shot of heavy rapidly accumulating snowfall Wednesday morning. In fact, winds will be fairly brisk from the northeast around the north side of the h7 low from Sweetwater County to South Pass, so South Pass will likely experience blowing and drifting snow given the wind and the snowfall Wednesday morning. The MET RKS has 21 knot sustained winds for RKS from 12Z to 18Z Wednesday. If we issue a winter storm watch for both slopes of the Wind River Mtns, we can capture all of South Pass. Therefor we will issue a winter storm watch for the Wind River Mtns valid from 06Z tonight through 00Z Thursday. Some locations of the Wind River Mtns could see upwards to 9 inches of snowfall in that time frame. 4 inches or so of snow could pile up over the Southern Wind Rivers from 12Z to 18Z Wed. The day shift can look at potential advisories for other surrounding zones as this storm nears. The watch would primarily address the impacts along Highway 28 over South Pass. This quick hitting system will exit rapidly east Wednesday night with snowfall dissipating. For Thursday, another shortwave will skim the southern Wyoming border but only produce a few light showers well south of I-80. Otherwise, expect partly sunny and milder conditions Thursday. High temperatures will run about 5 degrees warmer in Northern WY over what they will be Wed, and other areas 7 to 10 degrees milder. .LONG TERM...(Friday through Tuesday) Friday looks dry and warmer with breezy to windy areas in the favored wind corridors of the central and south. The next weather system and cold front moves into northern WY after midnight Fri night and into central WY during Saturday morning. The front pushes into the south during Saturday afternoon. There is usually a period of moderate snow for a few hours with a system of this nature along with a gusty north wind and falling temps behind the cold front. Have increased the chance of snow in most areas along and east of the continental divide. West of the divide, scattered snow will occur with the cold front passage with lesser impact. Snow will decrease and end from north to south Saturday night leading to a cold start to Sunday. Sunday should be dry for most locations with a few mountain snow showers possible over the higher peaks. Cold day on Sunday. Monday will be dry and milder for all areas. Then there is the potential for another weather system and cold front passage next Tuesday, possibly similar to the Saturday system. A little to far out to be bold and will keep low chance of precipitation in for next Tue. Colder highs next Tue. && .AVIATION...(For the 18Z TAFS through 18Z Wednesday) West of the Continental Divide...(KJAC, KRKS, KBPI, KPNA) The next storm system quickly overspreads the area with snow showers developing in the afternoon over the west, and then spreading southeast this evening. The best chance of snowfall looks to be from KKMM to KRKS after 06Z Wednesday. Overall KJAC seems again to be the least impacted Terminal although cannot rule out a period with MVFR conditions late in the afternoon/evening. East of the Continental Divide...(KCPR, KCOD, KRIW, KLND, KWRL) Low ceilings are still hanging in there at several terminals but should start lifting/scattering early afternoon. Most locations should then be VFR for the afternoon, but some mountain obscurations will persist. Another storm system moving into the area tonight will result increasing clouds this evening with MVFR ceilings developing in most locations, except perhaps part of the Big Horn Basin. IFR conditions in low ceilings and/or vis in snow could develop at KLND by around 08Z Wednesday. 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 the middle of this week. The current storm system that has been impacting the area is exiting off to the east early this morning. West of the Divide, there will not be a lot of precipitation until tonight, but it will remain fairly cool with fairly high min and max rh's. The next new storm system will spread another round of snow into the southwest and west by this afternoon and rapidly spread across the south and central portions overnight and continue into Wednesday before exiting the area. This next system will be a quick hitting, potent system with widespread snow across the Salt/Wyoming Range, Wind River Mountains and most of southwest and south central Wyoming up into parts of Fremont and Natrona Counties. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Storm Watch from late tonight through Wednesday evening for WYZ014-015. && $$ SHORT TERM...Lipson LONG TERM...AR AVIATION...Hulme FIRE WEATHER...Lipson