Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 332 AM EST Tue Jan 15 2019 Valid 12Z Tue Jan 15 2019 - 12Z Fri Jan 18 2019 ...California/The West... Days 1-3... Active weather pattern will continue through Thursday night across the West Coast bringing multiple rounds of heavy snow, particularly for the Sierra Nevada. WPC probabilities for more than 18 inches in 24 hrs increases each of the next three days. A trough will linger off the CA coast before shifting inland into OR tonight. A relative lull in precipitation to the Sierra Nevada returns this evening bringing moderate to locally heavy snows above about 5000ft. Moisture that spread inland ahead of this trough will result in snow accumulations across the higher terrain areas of southern/central Nevada into southern Utah in the 6-12 inch range according to WPC probabilities. Wednesday through Thursday night, a deep surface low will approach the Oregon coast and spread additional heavy snow across the High Sierra and much of the Intermountain West. 3-day totals across the portions of the Sierras will be several feet in the High Sierra and several inches elsewhere. Further more, surface high pressure shifting south over the Canadian Prairies provides MT with upsloping southeasterly flow with upper level divergence between a ridge axis and the deep low centered over Hudson Bay. This brings moderate probabilities for 6 inches to western MT. ...Great Lakes... Days 1-2... A shortwave trough/low crosses Ontario through tonight and Quebec Wednesday. Westerly flow south of this low will produce some lake effect snow off Superior/Erie and Ontario tonight with lake enhanced snow with the cold frontal passage over the eastern Great Lakes Wednesday. Moderate to high WPC probabilities for two inches are over the Tug Hill plateau. ...Midwest/Northeast... Days 2-3... A southern stream shortwave trough crosses the central Plains Wednesday night with some surface low development as it moves up the OH valley Thursday and to the northern Mid-Atlantic Thursday night. The progressive trough looks to start with a narrow stripe of snow/wintry mix on the north side of the precip shield over KS/MO Wednesday evening as it interacts with abundant high pressure to the north. This swath broadens as it shifts northeast with the chances for two inches increasing over PA/NY. East of the Appalachians, a cold air damming wedge from a leading surface high will make for subfreezing temps north from the central Mid-Atlantic. Models depict the wedge eroding Thursday night with flow becoming southerly. However, this is a common struggle for models especially when precipitation breaks out in the overrunning flow. A wintry mix is likely over the central Mid-Atlantic with potentially pockets of a tenth inch of ice as noted by the low WPC probabilities for a tenth inch of ice for Day 3. Overall the totals should be limited by movement and little moisture connection. Day 3 WPC probabilities for 2 inches are moderately high over the central Appalachians, PA and into upstate NY. Jackson