Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 342 PM EST Wed Feb 12 2020 Valid 00Z Thu Feb 13 2020 - 00Z Sun Feb 16 2020 ...Central Plains across Midwest and the Northeast... Days 1 and 2... The surface low with the southern stream trough will race northeast across the TN Valley and central Appalachians tonight before crossing southern New England tomorrow morning, and into the coast and offshore waters east of Nova Scotia tomorrow afternoon. Low-mid level warm advection and moisture advection combines with a 300 mb jet maxima streaking northeast from MO across the Great Lakes, New York, and New England to promote the snow moving across northern IL/IN/lower MI east across northern OH to interior NY/New England. Several inches are possible along the axis of snow, with bands of 3-6 inches likely. South of this axis, warming leads to snow changing to sleet/freezing rain across central IN/OH/northern PA/southeast NY/Southern New England. Light freezing rain accumulations are most favored in central OH and the Laurel Highlands and Poconos of PA, Catskills of NY, Berkshires and Worcester Hills of MA, and Monadnocks of southern NH. Freezing rain amounts will generally be less than a tenth of an inch. The event winds down as the low departs New England Thu. A strong cold front associated with the northern stream trough will cross the Great Lakes late Thu and Thu evening. This will set up lake enhanced and effect snow across southern lower MI into northern IN/northeast IL, and also downstream from lake Erie and Ontario in western NY. The approach of the ridge of high pressure and drier air aloft caps the lake effect snow potential. ...Colorado and NM... Day 1... A cold front banking up against the Front Ranges of CO and northern NM leads to a low-mid level frontogenesis maxima over these ranges. The models forecast a progressive low amplitude 700 mb shortwave to crosses these ranges tonight with a pool of enhanced moisture and loft. Favored upslope areas may received several inches of snow. The threat subsides tomorrow night as the wave departs and the available moisture declines. ...Pacific Northwest/Northern Rockies... Days 1-3... A relative minima in snow occurs tonight as as upper ridge from the eastern Pacific ridge moves onshore and then moisture return occurs during Thu as the next trough pushes into western WA late Thursday. Snow develops in the warm/moisture advection pattern in the WA Cascades, with accumulating snow likely at higher elevations. Snow picks up in coverage/intensity Thu night and Fri as a pair of 700 mb waves move east across the Pacific northwest and northern Rockies, with areas of enhanced moisture pooling and lift occurring with each wave, withe moisture/lift extending into the ranges of northwest WY Fri evening. Longer duration snows lead to locally heavy amounts in the WA Cascades to the Sawtooth/Clearwater Mountains of ID and mountains in Glacier National Park of MT. On Day 3 Fri night to Sat, a temporary weakening of the jet in the northern Rockies leads to less snow coverage/intensity. This is followed by another restrengthening of the jet by Sat morning coming onshore around 12z Sat according to the 12z ECMWF in WA. With this jet then persisting and moving inland,a long duration of snow in the WA Cascades leads to another round of heavy snow in favored upslope terrain in the mountains. Days 1-3 snow totals of 3-5 feet are possible in the windward terrain of the WA Cascades. 1-2 feet of snow are possible over the northern Rockies over the multi-day window. The probability of 0.25 inches of freezing rain is less than 10 percent Days 1-3. Petersen