Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 432 AM EDT Thu Mar 31 2022 Valid 12Z Thu Mar 31 2022 - 12Z Sun Apr 03 2022 ...Central Rockies... Day 1... Mid-level multi-vort shortwave will move southeastward out of western Montana and the Pac NW today in the left front exit region of a ~100kt jet streak. With a progressive flow and modest moisture (precipitable water values just over average values for late March/early April), snowfall will be on the light side (generally under 6-8 inches at the higher elevations). WPC probabilities for at least 4 inches of snow are moderate to high over the Absarokas and Bighorns in Wyoming, and low to moderate over western Colorado. ...Great Lakes and Northeast... Days 1-2... Mature cyclone wrapping up through Michigan this morning will continue to lift into Canada today, drawing in colder air in its wake over the Great Lakes. For the first part of Day 1, deformation band snow will quickly accumulate over the eastern U.P. of Michigan with rain changing to snow before ending over the northwestern Lower Peninsula. A few additional inches of snow is possible with lighter accumulations elsewhere as the precipitation will quickly end just after 18Z. As the main cyclone lifts away, a digging mid-level vort max will slip through MN/WI this morning and into/through MI and the Midwest overnight. This will help provide enough lift for scattered snow showers this evening into the overnight hours from Indiana eastward through Ohio. On Friday (Day 2), vort max will swing through Pennsylvania where additional snow showers and perhaps squalls are likely. Steep lapse rates, MUCAPE ~100 J/kg, and sufficient (though modest at best) moisture provide the ingredients for some snow squalls which may lead to difficult travel at times due to quickly lowered visibility. Upper trough moving through will also increase lake effect snows for areas of the Chautauqua Ridge in western NY and into the Tug Hill Plateau. A few inches of snow are likely in some areas, but WPC probabilities of at least 4 inches are low (though some CAM guidance showed more than 6 inches). ...Northwest... Days 1-3... Departing mid-level shortwave and modest jet streak will spread light snow over the Cascades and northwestern Montana Day 1 before a break in the precipitation as upper ridging moves in briefly overnight tonight. On Day 2, shortwave and surface cold front will move into WA/OR but with limited moisture. Again only light snow is forecast for much of the region with snow levels down to around 3000-4000 ft. This snow will cross into Day 3 for northern Idaho and northwestern Montana where several inches of snow are possible for the higher elevations. Snow levels will be around 2000 ft. For Days 1-3, the probability of significant icing of at least 0.25" is less than 10 percent. Fracasso ~~~ Key Messages for March 31 - April 1 Snow Squalls ~~~ * A strong cold front will push through the Ohio Valley today and the Northeast tonight. * Scattered snow squalls may develop and move over the Ohio Valley/Great Lakes region tonight. Snow squalls are likely during the day on Friday from the central Appalachians and Lower Great lakes toward the interior Northeast and Mid-Atlantic. * Intense but brief snowfall within these snow squalls can rapidly reduce visibility and lead to dangerous driving conditions, particularly on high-speed roadways. * Little to no accumulation is expected outside of the higher terrain, but slick spots may develop on bridges and overpasses.