Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 432 AM EDT Sat Apr 03 2021 Valid 12Z Sat Apr 03 2021 - 12Z Tue Apr 06 2021 Pacific Northwest... Days 1-3... An upper low over the southern Alaska Panhandle will move south-southeastward along the British Columbia coast through tonight before crossing the Pacific Northwest through Monday morning then slowing and turning east, crossing Wyoming through Tuesday. Its attendant cold front reaches northwestern Washington this evening and Wyoming by Monday. Heights will fall over the Cascades this evening as a narrowing corridor of PW values between 0.50-0.75" bisect the Olympics, spreading light snow to the higher elevations of the Cascades. Snow levels will lower from about 5000ft this afternoon to about 2000ft tonight as colder air filters in with moderate precip rates decreasing as the moisture plume shifts south ahead of the front. Day 1 snow probabilities are moderate for 6 or more inches in the far northern WA Cascades. The GFS remains more positively tilted and farther west with the resultant low, particularly on Monday. There is decent agreement by Monday night among the 00Z NAM/ECMWF/CMC/UKMET. The slowed pace of the system allows for a decent swath of snow over the northern Rockies of ID/MT/WY Monday into Tuesday. So Day 2 snow probabilities are limited to moderate for 4 or more inches in Glacier NP before they blossom on Day 3 with low to moderate probabilities of 8 or more inches across north-central ID, southwest MT and northwest WY. The probability of significant ice is less than 10 percent. Northern New England... Days 2/3... A stretched upper low will split off its southern extent off southeastern New England today and become negatively tilted as it pivots south of Nova Scotia 60W. Late Sunday it will loop back to the west near the southern tip Nova Scotia and wrap back some light snowfall (or mixed rain/snow as temperatures moderate) to portions of Maine and into far northern VT/NH Sunday night through Monday night. The UKMET remains the farthest west while the CMC is farthest east with decent agreement among the 00Z ECMWF/GFS which are between the other two and are preferred. Continued with conservative snow amounts given the uncertain evolution of the cutoff system and marginal thermal conditions to produce only light snow amounts. Due to the varied ensemble spread, probabilities of at least 4 inches of snow are only about 5 percent on Day 2. Jackson