974 FXUS65 KGGW 231053 AFDGGW Area Forecast Discussion National Weather Service Glasgow MT 353 AM MST Sun Feb 23 2020 .DISCUSSION... With precipitation expected to begin moving from central Montana into Phillips, Garfield, and Valley Counties within the next 12 to 15 hours, felt it was warranted to issue a Winter Weather Advisory for expected snow accumulations of 2 to 4 inches for all zones except Petroleum County. Forecast challenges will focus on the timing and amounts of the snowfall with this winter storm, including the impact of blowing and drifting snow, as well as a drop in temperatures for a few days. Weather pattern shows a near zonal flow today as the pronounced, cold, upper level low pressure trough moves up and over the continental divide tonight. In response, mostly sunny skies this morning will become cloudy and overcast from the west by mid-day today. Model precip data has lined up fairly well, showing an intial push of banded snowfall from west to east late tonight through early Monday. The exact track of the low pressure center and its associated dry slot is still uncertain. A few model differences remain, but consensus blends I used, have covered most of that uncertainty. For example, early Monday morning, the NAM wants to keep that first push of banded snowfall in a line from Opheim through Scobey and Culbertson, while the GFS keeps it in a line from Malta through Jordan and Circle. Overall, the effect of the dry slot seems to bring lesser snow amounts to Petroleum County. During the day on Monday, as the low pressure trough matures into a closed low center, the dry slot finally saturates and fills in the snow fall as the storm moves south through the remainder of eastern Montana and western North Dakota. Expect the last lingering snowfall to move south of our CWA during the early morning hours on Tuesday. A widespread 2 to 3.5 inches of snow is expected with this storm. The higher amounts seem to be favored along and north of US Highway 2 and along the higher elevations along either side of the Yellowstone River Valley. Mid level winds in excess of 30 kts, may be brought down to the ground with any precipitation, especially early Monday morning through Monday afternoon. If this happens to coincide with the banded snowfall, blowing and drifting snow would easily become a problem. But, it also may only be associated with the dry slot. Next shifts will need to closely watch these additional details for hopeful increases in confidence. Beginning Tuesday afternoon, a strong NW flow aloft and approaching high pressure from the west will drive any precipitation away and warm temperatures back up above normal. A brief short wave disturbance in the NW flow Wednesday night through Thursday will bring a slight chance for light precipitation. Friday through Saturday, another strong ridge of high pressure will keep things warm and dry for next weekend. ---BMickelson && .AVIATION... DISCUSSION: Today through tonight, a weak ridge of high pressure to our south, gives way to an approaching cold low pressure system from the Canadian Rockies. Ceilings will begin to drop later this afternoon and evening and snowfall is expected later tonight. After the winter storm spends most of Monday in the region, it will clear away by Tuesday morning. FLIGHT CONDITIONS: VFR this morning, MVFR this afternoon, then IFR to VLIFR in blowing snow late tonight and through the overnight hours. WINDS: Light and variable this morning, turning more out of the south and southeast up to 15 kts by this afternoon, then from the west up to 20 kts after 09Z in blowing snow. ---BMickelson && .GLASGOW WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 9 PM this evening to 5 AM MST Tuesday for Central and Southeast Phillips...Central and Southern Valley...Daniels...Dawson...Eastern Roosevelt... Garfield...McCone...Northern Phillips...Northern Valley... Prairie...Richland...Sheridan...Southwest Phillips...Western Roosevelt...Wibaux. && $$ weather.gov/glasgow |