Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 245 PM EDT Fri Apr 11 2025 Valid 00Z Sat Apr 12 2025 - 00Z Tue Apr 15 2025 ...Northern Mid-Atlantic to New England... Day 1... Complex April snowstorm to begin overnight and impact areas from northeast PA through New England with mainly high elevation heavy snow, but with the potential for even lower elevations to see light accumulations. Upper trough axis approaching the East Coast this afternoon will close off near southern MD and lift northeastward through Saturday. This will favor a surge of moisture northward into marginally cold air over the Northeast/northern Mid- Atlantic as mostly rain quickly changes to snow away from the coast, but perhaps a small area of sleet as well. Ptypes will be dependent on rates where temperatures are marginal (generally below 1,000ft), with some areas alternating between rain/snow. These rates are highlighted well in the latest 12z HREF, beginning around 06Z tonight along and near I-84 before lifting northward through the Interior Northeast and New England while weakening by about 15Z Sat. In addition, accumulation may be limited to grassy areas given mild ground/road temperatures and also struggle within a few hours of solar noon on Saturday as we approach mid- April. However, some more vigorous WAA over higher terrain and pronounced TROWAL will prompt areas of 1"/hr rates, with some pivoting of the deformation band on the northwestern periphery. It is this evolution that could yield several inches of snow (maybe as much as 6") by Saturday morning for places like the Poconos, Catskills, Berkshires, and southern Green/White mountains. Here, WPC probabilities for at least 4 inches of snow are generally 20-50%, but do increase to 60-80% for areas above 2,000ft. Lower elevations could see a slushy 1-3" from northeast PA and northern NJ through CT, northern RI, and MA. The northern extent of the snow is expected to ride along the Whites into western ME, with low chances (<10%) for amounts to exceed 4 inches. The ECMWF EFI is intriguing and has values of 0.7-0.9 for the impacted area with a maximum SOT of 2, which would signify an "unusual" event compared to mid-Aprils dating back to 2004 (the ECMWF reforecast period). ...Cascades to Northern Rockies... Days 1-2... A strong mid-level shortwave will move into WA and strengthen across ID/MT Saturday morning, promoting light to modest WAA- driven snow over NW MT into northern WY as the upper jet slips southeastward into the Plains. Temperatures will fall behind the front and lower snow levels to below 4000ft as precipitation lightens and then ends from west to east on Sunday/Sunday night. The system will be fairly progressive but it could snow moderately (>1"/hr) for a time Saturday evening. WPC probabilities for at least 8 inches of snow for the period are highest around Glacier NP and across the Little Belt Mountains (>30%). As a related cold front pushes southward with the progressing closed low moving eastward across the northern Plains, the northern CO Rockies have low chances for heavy snow Sunday night. ...Northern Minnesota... Day 3... As the aforementioned closed low moves eastward into the Upper Midwest by Sunday night it is forecast to strengthen and dynamically cool the column, leading to potentially local heavy snowfall bands. Currently, WPC Day 3 snowfall probabilities for at least 4 inches are 20-40% across far northern MN. The probability of at least 0.10" of freezing rain across CONUS is less than 10%. Snell