658 FXUS65 KTFX 221538 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 838 AM MST Tue Dec 22 2020 .UPDATE... Surface pressure analyses reveal a 993 mb surface low positioned over northern Blaine county, moving away to the east. The associated trough, and leading edge of a Pacific front, trails back through southwest Montana. A stronger cold front arriving from Canada is advancing through North central Montana, presently along a line from near Chester to Choteau. Areas of light snow are moving through central and southwest Montana with the Pacific front. Of greater concern for now, areas of moderate to at times heavy snow have developed along and behind the cold front in North-central MT. Additionally, rapid pressure rises are causing strong north-northwest winds gusting to 50 mph with areas of blowing snow following that quick half to one inch of new snow accumulation. The strongest winds will peak for about an hour or two, but then continue with breezy Northwest winds through the afternoon. Considered all together, the story describes rapidly changing weather; anyone heading out today should be prepared for variable conditions. Note as well that temperatures will be falling through the day. The forecast was updated to better match observed trends in precipitation, winds, and temperatures. && .SYNOPSIS... A cold front and low pressure system move east across the region today bringing gusty west to northwest winds, colder temperatures and periods of snow or snow showers to most areas. Snow accumulations will be light for most areas outside of the mountains, but travelers should expect quickly changing conditions due to snow and winds. Colder conditions will be short lived with a return to above average temperatures and dry conditions Thursday and Friday. && .AVIATION... 450 AM MST Tue Dec 22 2020 (22/12Z TAF period) VFR conditions early this morning will degrade today as low pressure tracks across the region and snow showers increase across the area. Expect primarily MVFR conditions with showers passing through SW MT this morning behind the initial Pacific cold front shifting east across the area. Meanwhile, low clouds will move back into the KCTB area early this morning as a Canadian airmass and wind shift to north spreads south from Alberta. Gusty southwest to west winds at most terminals this morning will turn to northwesterly as low pressure moves east of the area and the Canadian airmass spreads south and east across the area. Additional snow showers and lower cloud ceilings will increase across much of the area this afternoon along with stronger surface winds from the NW with gusts to 40 kts possible in most areas. Brief periods of IFR conditions are possible in snow showers this afternoon at most terminals with improving conditions from NW to SE across the area this evening. Hoenisch Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 450 AM MST Tue Dec 22 2020/ A fairly well defined shortwave trough moves across the area today with surface low pressure emerging east of the Rockies in extreme SW Alberta this morning tracking SE across MT today while deepening. A Pacific cold front is first to move east across the area early this morning with snow showers moving into areas near the continental divide first, then across portions of SW through mid morning. West winds increase across north-central MT this morning behind this front through little precipitation is expected with it across the plains. Meanwhile, a colder airmass in Canada sweeps south across the border this morning as the surface low moves east with winds at the surface and aloft shifting to northwesterly and increasing. A combination of surface pressure rises and increasing NW flow will support wind gusts in the 35-45 mph range for much of the area later today with strongest winds aloft sliding SE across eastern MT this afternoon. Eastern portions of north-central MT will have the best chance at seeing gusts in excess of 50 mph beneath these stronger winds aloft, particularly across portions of Blaine, Fergus and Judith Basin counties where the High Wind Watch has been upgraded to a warning. Snow showers will spread S/SE with the colder airmass today with potential for a band of enhanced snow along the leading edge of the colder air with snow showers persisting into this evening near the mountains before drier air moves in behind the departing weather system overnight. Snowfall amounts have changed little from previous forecasts with most lower elevation areas likely to see less than an inch of snow accumulation with somewhat higher amounts in the vicinity of the Little Belt and Snowy mountain ranges where snow showers will be more numerous into this evening. Several inches of snow are expected at higher elevations along the continental divide as well as across the mountains of central and southwest MT. A winter weather advisory continues for areas above 5000ft where impacts to travel across passes are possible at times. The colder airmass settles briefly across the area tonight with decreasing winds and clearing skies before upper level ridging builds quickly back into the region from the west on Wednesday. Dry and milder conditions are expected through Christmas Day as the upper level ridge progresses east across the area with afternoon temperatures warming back to the upper 30s to upper 40s for most areas. The upper level ridge flattens this weekend with a return to unsettled westerly flow from the Pacific going into next week. Temperatures look to trend back toward seasonal averages this weekend into next week with some chances for precipitation, though at this point moisture and timing with the next round of Pacific disturbances is fairly uncertain. Hoenisch && .PRELIMINARY POINT TEMPS/POPS... GTF 44 14 35 24 / 80 40 0 0 CTB 36 10 31 22 / 100 60 0 0 HLN 40 16 32 16 / 100 70 0 0 BZN 45 11 30 8 / 90 70 0 0 WYS 32 -6 17 -5 / 90 60 0 0 DLN 40 8 25 9 / 90 30 0 0 HVR 41 13 32 22 / 70 40 0 0 LWT 43 11 31 19 / 80 90 0 0 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 5 PM MST this afternoon above 5000 feet for Central and Southern Lewis and Clark...Jefferson... Northern Rocky Mountain Front...Southern Rocky Mountain Front. Winter Weather Advisory until 8 PM MST this evening above 5000 feet for Cascade...Judith Basin...Meagher. High Wind Warning until 8 PM MST this evening Blaine...Fergus... Judith Basin. && $$ http://www.weather.gov/greatfalls