Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 451 AM EDT Tue Apr 11 2023 Valid 12Z Tue Apr 11 2023 - 12Z Fri Apr 14 2023 ...Pacific Northwest... Day 1... An upper trough moving into the Pacific Northwest this morning is followed by a closed low that will reach the WA/OR border late tonight. Snow levels are around 2,000 feet today, lowering to 1000ft or locally less late tonight into Wednesday. Snowfall totals will be highest in the higher elevations with Wly flow aiding orographic lift. The Olympics and Cascades for Day 1 feature high WPC probabilities for >6" of snowfall and moderate probabilities (40-60%) in the Clearwater and Salmon River Mountains of ID and the highest OR Coast Ranges. The upper low late tonight will contain exceptionally cold temperatures for mid-April, enough to support minor snowfall accumulations down to around 500ft. Even along the I-5 corridor south of Seattle and north of Portland could see a coating of snow, but should any of the snowfall accumulate, it would be more of a nuisance snowfall event for these locations with accumulations generally confined to grassy surfaces. ...Northern Rockies onto the Northern High Plains... Days 2/3... The upper low swings from the Pacific Northwest to Idaho Wednesday/Wednesday night before pivoting northeast over south-central/eastern MT Thursday/Thursday night. Ample Pacific-sourced moisture will focus over the northern Rockies Wednesday night/Thursday with lee-side cyclogenesis focusing NEly flow over mainly MT ranges along with additional moisture from the western Gulf via the Plains. Moderate Day 2 probabilities for >6" are over the Clearwater Mtns of ID and most SW/south-central MT and around Yellowstone in WY. Day 3 snow probs are more expansive and higher over much of the same areas. As the low tracks over the north-central Plains Thursday night, bands of rain/snow become all snow in the heavier/more dynamic activity. As of now Day 3 snow probabilities are low for >2" over central and northeastern MT into western ND. The probability for icing over 0.1" is less than 5% Days 1-3. Jackson