Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 355 AM EST Thu Jan 24 2019 Valid 12Z Thu Jan 24 2019 - 12Z Sun Jan 27 2019 Great Lakes Region ------------------ An active period of lake enhanced and lake effect snow owing to cyclonic flow from a large low-mid level low over the Hudson Bay region has begun across the Great Lakes, and episodes of lake effect snow are expected to continue through the upcoming weekend. Much below normal temperatures should lead to gradually increasing ice coverage on the lakes over the coming days, but for now ice coverage is low enough to warrant full lake effect potential through the next three day forecast period. A weak shortwave trough associated with an arctic cold front crossing the Midwest states will slowly move east across the Lakes through Thursday night. Expect light snow along this slow moving front from northeast Minnesota and then across the Lakes through Thursday night. Low level northwesterly flow behind the front will steepen low level lapse rates and result in lake effect snow bands primarily affecting the Upper Peninsula and northern Lower Peninsula of Michigan on Day 1, and then downwind of lakes Erie and Ontario on Day 2. Central Appalachians to Upstate New York ---------------------------------------- Northwesterly flow behind the cold front crossing the East Coast region on Thursday results in enough cold air advection for a period of upslope snow over the crest of the central Appalachians and extending northward across much of Upstate New York and northern New England. Given the quick progression of the front and most of the heavier QPF being in the warm sector of the low, amounts should be limited to under 4 inches in most cases. Northern Plains --------------- An elongated shortwave embedded within progressive northwest flow along with an upper level jet max overhead in the vicinity of a stationary front will support some warm advection light snow across mainly North Dakota during the day 3 period on Saturday, with amounts generally two inches or less. This is in advance of a stronger disturbance that is progged to sink southward from Canada just beyond the end of this forecast period. Central and Northern Rockies ---------------------------- Some light to moderate upslope snow is expected across the central and northern Rockies behind an arctic cold front, mainly through Friday afternoon. Weak shortwave energy in northwest flow aloft and upper level divergence will promote enough vertical ascent for several inches of snow from southwestern Montana to central Colorado, with low-moderate WPC probabilities for 4+ inches for the favored terrain. The probability for significant icing is less than 10 percent nationwide days 1-3. D. Hamrick