Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 358 AM EST Sun Feb 09 2020 Valid 12Z Sun Feb 09 2020 - 12Z Wed Feb 12 2020 ...Upper Midwest to the Northeast... Days 1-2... A northern stream shortwave will shift east across the Upper Midwest through tonight. Low-to-mid level frontogenesis along with increasing upper jet dynamics will continue to support moderate to heavy snowfall bands developing north of the associated low track. Ample moisture and strong dynamics (across southern MN and at least into WI this afternoon) will continue to allow 1 to 2 inch per hour snow rates and have raised the expected snow in the narrow heavy bands. Snow probabilities for 8 or more inches are moderately (starting at 12Z today) from southeast MN across south-central WI. The increasing jet shears the storm and quickly ejects it across MI this evening and Maine Monday morning. Decreasing snow intensity is expected as the low crosses central MI with snow probabilities high for four or more inches across northern Lower MI. Generally lighter snow and limited to higher elevations as precip spreads across the Northeast in the warm air advection pattern preceding the low. Moderate probabilities for 4 or more inches are in the Day 1.5 outlook for terrain in NY State and New England including the Catskills, Tug Hill and Adirondacks, Green and White Mountains. WPC PWPF indicates little potential for widespread heavy amounts across the Northeast on Day 2 (ending 00 Tuesday). ...Southwest/Central and Southern Rockies onto the Southern High Plains... A rather positively tilted trough over northern CA this morning closes off today as it approaches southern CA. This low curls inland over the northern Baja Monday before shearing/opening over the AZ/Mexico border Tuesday. The remnant trough then ejects east across the southern Rockies/NM Tuesday night. Day 1...The combination of a strong ridge over the Pacific Northwest and northern Rockies and lee side surface low development over eastern NM makes for and northeasterly upslope flow to the CO Rockies today with moderate snow probabilities for the eastern slopes). Decent Pacific moisture convergence along the trough axis brings mountain snows (snow levels around 4000ft along the trough axis and high snow probabilities of 4 or more inches for higher terrain) to much of the CO Rockies and southern UT mountains, the taller mountains outside Las Vegas, and the San Bernadino mountains of southern CA. Day 2... The inland moving low over far northwest Mexico shifts the QPF axis farther south with continued strong Pacific moisture advection increasing coverage and intensity. The persistent ridge to the north and renewed lee side cyclogenesis brings increased upslope flow for the southern Rockies/southern High Plains. Snow probabilities for 6 or more inches are moderate to high over the highest parts of the San Bernadino Mountains again, the Mogollon Rim and White Mountains in AZ, and the San Juans/Sangre de Christos in CO/NM. 10 to 20 percent probabilities of 6 or more inches spread across the southern high Plains of northeast NM into southeast CO with snow levels. Day 3... The addition of Gulf of Mexico sourced moisture as well as the approaching trough allows further precip intensity increases as the convergent upslope flow shifts south across NM. Snow probabilities are moderate to high for 6 or more inches over the White Mountains of AZ and Sacramento Mountains of NM and moderate over much of eastern NM into the TX Panhandle. For Days 1-3, the probability of significant icing (0.25-inch or greater) is less than 10 percent. Jackson