497 FXUS65 KBYZ 241015 AFDBYZ Area Forecast Discussion National Weather Service Billings MT 315 AM MST Tue Dec 24 2019 .DISCUSSION... A wave moving northeast out of the Great Basin was beginning to bring snow to the southwest mountains early this morning. Low clouds and fog over northeast Montana were also gradually moving south into far northeast portions of the area. Patchy fog is possible for northeastern areas this morning. As the wave continues to move northeast through the region and upper troughing shifts into the area today, snow will spread over the western mountains, with mainly dry conditions expected elsewhere. A few inches of snow accumulation are possible over south and west facing slopes of the southwest mountains. A few light rain or snow showers may spread out onto the western foothills as well. Today will be cooler than previous days with highs in the 30s and 40s, lowest over eastern areas. As upper troughing shifts east over the region today and tonight, a closed low sliding east over southern Canada will turn winds around to the north and bring cooler air into the area on Christmas. At the same time, a surface trough/low moving northeast out of Wyoming into South Dakota will transport moisture into the Northern Plains and interact with the weak cold air advection and upslope flow over the area. Latest progs and guidance are starting to become more clear on an area of light precipitation forming over southeast Montana and northeast Wyoming on Christmas, shifting east into the Dakotas during the evening as the aforementioned surface low slides east. Temperatures look to range from the 40s over western areas to the lower 30s over eastern areas. Western and central areas could see a rain/snow mix with weak upslope flow, while areas generally south and east of a Fort Smith to Hardin to Miles City line have the best potential at seeing some light snow accumulations (1 to 3 inches for lower elevations and 3 to 6 inches for the Bighorn Mountains). Latest guidance indicates low potential for freezing precipitation so have kept any mention of it out of the forecast, but will continue to monitor the potential. Temperatures are forecast to drop into the teens and 20s Christmas night. STP Thursday through Tuesday... Troughiness lingers over the region on Thursday with another disturbance tracking across Alberta and Saskatchewan. While flow aloft remains weak during this period models indicate drier air working its way into the area which generally should reduce precipitation chances. Any snow on Thursday should be limited to the mountains. Thursday will be the coolest day of the week with most highs in the 30s. Winds turn westerly Friday as ridging begins building into the Pacific Northwest. This scours out the shallow cold airmass and brings dry conditions through the weekend. Expect strong winds to develop along the foothills and remain steady with some gusts near 50 mph through the period. Ridge breaks down early next week but zonal westerly flow will continue dry conditions with seasonal to above normal temperatures. borsum && .AVIATION... Southwest flow aloft with high clouds streaming over the region. Weak are of surface low pressure from southeast Wyoming extending through south central Montana producing light winds with northerly winds northeast of this low pressure. These northerly winds are bringing low clouds and fog to parts of northern Montana and this fog is trying to move southward in the river valleys. Expect this fog to remain north of a KMLS-Roundup-Judith Gap but could see some reduced visibility for a period at KMLS. Otherwise expect VFR conditions. borsum && .PRELIMINARY POINT TEMP/POPS... Tdy Wed Thu Fri Sat Sun Mon ------------------------------------------------------- BIL 043 029/042 027/040 025/041 027/042 027/044 029/045 1/B 12/O 21/B 00/B 00/B 00/U 10/U LVM 044 031/041 026/037 023/037 024/039 025/042 027/043 2/O 22/O 21/U 00/N 10/N 01/N 11/B HDN 043 024/040 022/038 019/040 022/041 020/043 022/045 0/B 13/O 21/B 00/U 00/U 00/U 11/B MLS 037 021/035 020/035 019/039 022/037 019/039 022/041 0/B 03/S 21/B 00/U 00/B 00/U 10/B 4BQ 041 022/035 021/034 018/038 020/037 018/039 021/040 0/B 14/S 31/B 00/U 00/B 00/U 10/B BHK 035 019/030 018/029 016/036 019/033 017/036 019/038 0/B 03/S 32/S 00/U 00/B 00/B 01/B SHR 046 024/040 020/036 014/038 015/039 017/042 019/043 0/U 25/O 42/S 00/U 00/B 00/U 11/B && .BYZ WATCHES/WARNINGS/ADVISORIES... MT...None. WY...None. && $$ weather.gov/billings