Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 358 PM EST Tue Feb 15 2022 Valid 00Z Wed Feb 16 2022 - 00Z Sat Feb 19 2022 ...Rockies... Days 1-2... A potent upper low is set to track south through southern California this evening with an associated low pressure system focused in southern Nevada. The upper trough axis at 250mb will remain positively tilted as it tracks through the Southwest with an emerging jet streak's left exit region positioned over the central Rockies. Meanwhile, a more potent jet streak in British Columbia will also favor vertical ascent downwind over the northern Rockies. Another upper level disturbance is being directed towards the Northwest Wednesday morning which will have some remnant Pacific moisture accompanying it. This combined with some modest upslope enhancement behind a trailing cold front should produce some heavy snowfall, primarily focused in the northern and central Rockies through Wednesday night. For D1, the taller ranges of Montana and Wyoming are set to see some of the heaviest totals tonight but as the aforementioned upper trough digs south through the Great Basin later in the day on Wednesday, snowfall rates will tick up across the central Rockies by late Wednesday. The taller mountain ranges of the Rockies have the highest probabilities of snow totals exceeding 4 inches. By Wednesday night and heading into Thursday, the core of the heavier snowfall totals from the Colorado Rockies on south into northern New Mexico. For the period, some of the highest peaks of the CO Rockies could top 10-12 inches. ...South-Central Plains to Great Lakes... Days 2-3... A closed mid-level low ejecting out of the Four Corners will gradually open into a negatively tilted trough across the Central/Southern Plains Thursday before lifting northeast towards the Great Lakes. Farther north, a potent upper level trough tracking across southern Canada will act to create a confluent zone over the Upper Midwest. Model guidance as of this afternoon remains split into two camps with NCEP model guidance favoring a more northern storm track with non-NCEP guidance staying on a more southerly track. In terms of what these two camps agree upon, moisture flow increases with PW anomalies reaching +2.0 just south of the elongated frontal boundary draped over the Middle Mississippi Valley on north through the Lower Great Lakes. This ample moisture source is being transported within a strong 850mb LLJ out ahead of the primary upper trough. Combined with robust forcing for ascent from jet streak coupling (one over the Great Lakes, the other emerging out of Texas), expect widespread precipitation with a variety of winter weather types from the southern High Plains to the Great Lakes. Forecast spread has continued to lessen to some extent but there remains latitudinal spread that leads to both larger variations in snowfall coverage and precipitation type concerns. That said, the general swath of potentially heavy snow is increasingly likely north and west of the low track from portions of Kansas to Michigan. The latest WPC probabilities for 4 inches are moderate to high from northern OK through the Midwest and into the Great Lakes while the greatest signal for 8 inches or is oriented from eastern KS toward Chicago and into central Michigan. South of this heavy snow axis, a corridor of sleet and freezing rain is expected as a warm nose aloft overruns subfreezing temperatures at the surface. There remains uncertainty as to both totals and the axis of where the heaviest ice accumulations occur. WPC probabilities for 0.1" of freezing rain are as high as 50 percent across north-central Missouri and into western Illinois within a broad swath of more than 10 percent extending from southeast KS through southern Michigan, which includes the Detroit metro area. Mullinax