Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 401 PM EST Thu Jan 02 2020 Valid 00Z Fri Jan 03 2020 - 00Z Mon Jan 06 2020 Days 1-3... ...Pacific Northwest to the Northern Rockies... An amplified upper ridge is forecast to shift east from the West Coast into the Intermountain West late Thursday into Friday. At the surface, a warm front is expected to lift across the Pacific Northwest -- supporting high elevation snows across the northern Cascades and Rockies. Outside of the higher elevations of the northern Cascades, expect little threat for heavy accumulations through late Friday. A greater potential for more widespread heavy snow accumulations is forecast to return early Saturday as a well-defined shortwave trough and its associated cold front move inland. Strong onshore flow, along with favorable upper forcing is expected to support locally heavy snow accumulations, with WPC guidance indicating high probabilities for amounts of 12-inches or more for portions of the Olympics and northern Cascades. While this system is forecast to move progressively east of the Rockies by Saturday evening, an upstream shortwave is expected to quickly follow, bringing additional heavy accumulations as it moves inland on Sunday. ...Northeast and Central Rockies... A series of southern stream shortwaves are forecast to lift from the southern Plains/western Gulf Coast region northeastward ahead of an amplifying northern stream trough digging from the northern Plains to the lower Ohio valley late Friday and Saturday. Models continue to differ on the degree of phasing of these streams and the overall track and intensity of the associated surface low that is forecast to move from the upper Ohio valley to the Northeast coast on Saturday. Given the model spread and poor run-to-run continuity, cannot rule out the potential for a more significant system with greater impacts; however, the general trend of the 12Z guidance (especially the ECMWF and UKMET) was toward a weaker and more southerly low track -- producing only light snow accumulations across portions of the Northeast late Saturday and Sunday. The latest WPC probabilities show the greatest threat for snow accumulations of 4-inches or more centered across the higher elevations of Upstate NY, Vermont and New Hampshire. Meanwhile, strong northwest flow on backside of the system will support snows into the central Appalachians, with several inches possible along the Allegheny Mountains in West Virginia Saturday night. The probability of significant icing (0.25 inch or greater) is less than 10 percent. Pereira