237 FXUS65 KRIW 072048 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 148 PM MST Sun Nov 7 2021 .SHORT TERM...(This evening through Monday night) Issued at 110 PM MST Sun Nov 7 2021 The longwave H5 trough remains centered off the PacNW Coast, with deep southwesterly flow continuing across WY during the next 24 hours. The first embedded shortwave exited to the northeast this morning, with snow ending across greater YNP. The central of the midlevel southwesterly jet, and the associated cold front, will sweep southeast this evening and tonight, drawing colder air into the state. While this isn't a significant cold air plunge, it will be a noticeable difference from the near record highs the past couple days. The southwesterly flow will continue to bring midlevel moisture across the region tonight. Another weak impulse will sweep through tonight, embedded in the flow, which will help produce some light precipitation again tonight. This will focus more on Southern WY, stretching into the I-25 corridor. Most precip will be rain, with a brief snow switchover later tonight, but overall lift will be low, keeping precip light. Best snow chances will be along the southern Wind River Range, which will get some better orographic lift, and will see up to 3 inches in the higher elevations. The Bighorn range will also be better aligned for some orographic lift, and may see an inch or two through sunrise. .LONG TERM...(Tuesday through Sunday) Issued at 110 PM MST Sun Nov 7 2021 A strong Pacific H5 low positioned just off the S. Alaska Panhandle sets up a negatively tilted upper level trough across the Pacific NW. Along the southern end of the trough, a shortwave will slide across the region Tuesday night into Wednesday. The most recent model trends have shown increased confidence in a open flow of Pacific moisture, which could bring some significant snow for the western mountains. With the orientation of the trough and southwest flow across the region, this will likely remain a primarily west of the Divide event. Still a little far out in the forecast to provide too much insight on snow amounts or potential highlights, but likely will see at least Advisory amounts across the western mountains based on the available moisture with this system. Gusty strong winds will also occur across the usual Wind Corridor Tuesday with the incoming wave, but jet support is minimal and winds do not look to hit high wind criteria. By Wednesday, the trough becomes more negatively tilted, which slides the moisture across the north and central areas. The Bighorns could see a quick shot of decent snow Wednesday and Wednesday afternoon. I should note here that temperatures will not be especially cold with this event, so lower elevations of the Bighorn Basin will likely start as rain before transitioning to snow Wednesday afternoon. By later Wednesday afternoon, the trough axis pushes east of the area, taking the precipitation with it. However, this will also result in strong northwest flow across the region, which will keep chances of snow across the western mountains through the end of the week. The negative tilt of the trough tears apart the original closed low, but by Wednesday night, the closed low begins to redevelop across the Northern Plains/Great Lakes area. This will tighten the pressure gradient across the region and establish some better jet support for a potential strong to high wind event across Johnson/Natrona Counties. Both the GFS and ECMWF indicate 55 to 65 kts at 700mb across this area during the day Thursday, combined with a tight gradient associated with the strengthening closed low. MOS has not yet caught onto the potential for high winds, but will be something to monitor over the next several days as the models continue to come into agreement on the position and strength of the low. Temperatures will be seasonal through much of next week. Tuesday continues to look like the warmest day of the week with highs expected to be about 5 degrees above normal. With the passage of the trough Wednesday, temperatures drop below normal by Thursday, but look to increase again as we head into the weekend, as a ridge builds in behind the trough, which becomes positively tilted across the Central Plains by Friday. && .AVIATION...(For the 18Z TAFS through 18Z Monday afternoon) Issued at 1036 AM MST Sun Nov 7 2021 Precipitation continues to end this afternoon across the west, and as a result, all sites should remain VFR through the period. KJAC could see occasional MVFR ceilings through 21Z this afternoon as some low clouds could stream across the site briefly at times as the showers end. Mountain obscurations will continue through 09Z Monday across the far west. KBPI and KPNA could see some showers or late tonight before showers completely end by Monday morning. Gusty winds across KCPR and KRIW will continue this afternoon. KCPR could see breezy winds gusting 20 to 25 kt this afternoon while KRIW should not see gusts over 20kts. Winds will diminish by sunset. && .FIRE WEATHER... Issued AT 110 PM MST Sun Nov 7 2021 Minimal fire weather concerns during the next several days, with light rain at lower elevations and an inch or two of snow for higher elevations. Humidity levels remain above 30 percent through most of next week. Main concern will very increased winds Tuesday and Wednesday. Frequent gusts above 40 mph are possible both days, from the southwest on Tuesday and the northwest on Wednesday behind a cold front. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...Straub LONG TERM...Hensley AVIATION...Hensley FIRE WEATHER...Straub