Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 410 AM EST Fri Jan 07 2022 Valid 12Z Fri Jan 07 2022 - 12Z Mon Jan 10 2022 ...Pacific Northwest to the Central Rockies... Days 1-2... An Atmospheric River shifts inland today ahead of a trough axis that is approaching the WA/OR coast early this morning. Mountain snows will occur across the northern Great Basin to northern Rockies today shifting southeast to the CO Rockies tonight/Saturday. Day 1 WPC snow probabilities are moderately high for an additional 8 inches for the WA/OR Cascades, the Salmon River and Sawtooth of ID and the Bitterroots and ranges of Glacier NP along with the Yellowstone area then moderate probs for more than 6 inches for the northwestern CO ranges for Day 1.5. ...Great Lakes... Days 1... Cyclonic flow from the developing low off the Northeast and the associated upper trough stretching back over the Great Lakes will results in continued CAA across the Lakes today, persisting for the eastern Lakes this evening. The pivoting bands will persist over SW MI, and off lakes Erie and Ontario where additional 4 to 8" are progged. Shortwave ridging will cut off LES by this afternoon for MI and later this evening for Erie and Ontario. ...Ohio Valley/Central Appalachians through the Northeast... Days 1-3... A negatively tilted shortwave trough over the central Mid-Atlantic will quickly lift northeast up over New England today with a rapidly developing coastal low currently off the southern Mid-Atlantic coast lifting north to Nova Scotia by mid-afternoon, continuing to produce a swath of heavy snowfall for the I-95 corridor. As the coastal low strengthens, both synoptic and mesoscale ascent will intensify, as WAA spreads moisture across eastern New England. Confidence has increased for the 1" to 2"/hr snowfall rates will spread from western CT northeast through Boston, MA and along the coast of ME with a modest TROWAL angling onshore from eastern MA northward leading to snowfall maxima in both southern New England and Down East Maine. WPC probabilities have moderate probabilities for over 6 inches around Boston and 30 to 40% for one foot in far eastern Maine. Cold high pressure spreads east from the Midwest today and across the Northeast through Saturday. As this high begins to shift offshore late Saturday, return flow and some WAA associated with a warm front draped from a low moving across Canada will spread precipitation back into the region. This precipitation will move into a region that initially is cold and dry at the surface, but is well above 0C aloft through the aforementioned WAA. Wet-bulb temperatures are forecast to remain below freezing so precipitation is likely to fall as freezing rain across parts of the Mid-Atlantic and into the Northeast. The Day 2.5 ice probabilities for a tenth inch are moderate across much of central and east-central PA across southern interior NY and the Berkshires/Litchfield Hills of MA/CT. Jackson ~~~ Key Messages for the Mid-Atlantic to the Northeast Winter Storm ~~~ - Moderate to heavy snow will lift from across southern and eastern New England this morning, persisting over eastern Maine this afternoon. - Snow will be heavy, reaching 2"/hr at times. This will produce a swath of snow reaching 6+ inches from the NYC metro northeast through southern New England, including Boston, MA, and across Down East Maine. - This snowfall, combined with cold temperatures and gusty winds, will create dangerous travel due to significantly reduced visibility and slippery roads.