718 FXUS65 KRIW 260939 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 239 AM MST Sat Nov 26 2022 .SHORT TERM...Today through Monday night Issued at 238 AM MST Sat Nov 26 2022 The weather will take a more active turn today, after a quiet two days to start the long holiday weekend. A weak cold front and shortwave now over Montana will sweep southeastward across the area today into this evening. The system is a fast mover and does not have a ton of moisture to work with. Therefore, snowfall amounts should remain below advisory level. Some precipitation could even start as rain before temperatures wet bulb and turns over the snow. A few inches will be possible in the northern mountains. In the lower elevations, most models are honing in on places like Casper where there could be a quick inch or two of snow. However, most areas will have a chance of some accumulation. There will also be the potential for some banded snow, so accumulations could vary over short distances. The other potential will be a flash freeze in some locations, especially in areas away from the population centers when temperatures drop. Most snow should end late this evening, with only a few snow showers across the west. Any snow showers on Sunday should be restricted to the western mountains with the orographics. The main concern will be wind, possibly high wind. The factors for the high wind will be a tightening pressure gradient ahead of a more potent shortwave and cold front dropping in from the north. In addition, there will be a fairly strong 130 knot jet moving in from the west to enhance downward momentum. The factors against are only four height contours across the area, usually we would like to see five. At 700 millibars, winds approach 50 knots but are less in some areas, like around Casper. Since the strongest wind would not be until late Sunday or Sunday evening, there is still time so for now we will likely punt to the day shift for any potential High Wind Watches. Wind should decrease late tonight as the front moves through. Now for the snow portion of the system. Snow should increase in the northwestern mountains Sunday night as the front approaches, westerly flow increases and the jet streak approaches. At this point, the steadiest and heaviest snow in this locations will be Sunday night, especially after midnight. As for amounts, it looks to be advisory to borderline warnings. Still time to watch it though. As for east of the Divide, there is more uncertainty. The snow will likely be driven mainly by dynamics through Monday. That means mainly banded snow that is hard to pinpoint this far out. So for now, we made few changes. Another jet driven band of snow is possible across southern Wyoming, with the GFS being especially bullish. The other models are further south though. So again, a lot of uncertainty. The third question is how much upslope can occur in the favored north to northeastward flow areas like Casper and Lander, as lee cyclogenesis occurs over Colorado. The X factor will be how much moisture will be present. At this point, Casper looks to have the best chance with lesser chances further west. But again, confidence in the details is low. So to sum up, confidence is fairly high for a decent snowfall across the western mountains. In southern Wyoming and east of the Divide, some snow is likely but details and placement of the heaviest snow are still highly uncertain. .LONG TERM...Tuesday through Friday Issued at 238 AM MST Sat Nov 26 2022 Snow will linger across the forecast area Tuesday morning, as the base of the trough moves over UT/CO. This will keep all the associated dynamics over this area and refocus the potential snowfall to western portions. Bitter cold temperatures will occur Tuesday, with highs struggling to reach 20 degrees during the day Tuesday. A ridge will quickly rebuild over the region Wednesday night into Thursday, as the next storm system digs over the PACNW. Pacific moisture will return over western portions under west- southwest orographic flow aloft by Friday, resulting in snow over this area. && .AVIATION...For the 06Z TAFS through 06Z Sunday Issued at 922 PM MST Fri Nov 25 2022 West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals. The start of the TAF period will have VFR conditions, until a cold front moves through Saturday morning. Light snow looks to develop for KJAC around 13Z with conditions to MVFR or IFR as snow picks up in intensity through the day. KJAC will see snow ending by 21Z with conditions returning to VFR. KPNA, KBPI and KRKS will see VCSH by late morning with not much of a impact expected. KPNA and KBPI will see snow ending by 00Z Sunday, while KRKS will have precipitation end by 04Z. East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals. VFR conditions will occur for KCOD and KWRL, until light snow moves into KCOD and KWRL between 13Z to 15Z. MVFR and IFR conditions will be possible at times especially around 16Z when the heaviest bands of snow move through. Snow will end by around 22Z for both terminals with conditions improving to VFR. VFR conditions will remain at KRIW, KLND and KCPR until conditions begin to deteriorate around 21Z with snow showers developing. KCPR may start off with a period of rain or wet snow, but should quickly transition over to all snow by 23Z. Conditions should improve by the end of the period as VFR conditions return to all terminals. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .FIRE WEATHER... Issued AT 238 AM MST Sat Nov 26 2022 A weather system will move across the state today and bring some snow showers, mainly to western and northern Wyoming. A gusty breeze will develop this afternoon. Relative humidity will remain above critical levels. Mixing and smoke dispersal will be generally poor in the afternoon. Strong to potentially high winds will be possible in the favored areas Sunday with more substantial snow in the west Sunday night into Monday. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...Hattings LONG TERM...LaVoie AVIATION...Ross/Dziewaltowski FIRE WEATHER...Hattings