Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 416 AM EST Thu Mar 07 2019 Valid 12Z Thu Mar 07 2019 - 12Z Sun Mar 10 2019 ...Western United States... Days 1-3... A closed/cutoff low initially located over the Salish Sea over the BC/WA will open and drift east to the northern Rockies through Saturday. A southern stream mid-level ridge axis over the CA coast has cutoff Pacific moisture inflow across the Great Basin with precip rates decreasing today. However, the next southern stream shortwave trough reaches the central CA coast tonight which will bring a return of Pacific moisture along with a strong jet moving zonally across southern CA allows snow elevations to drop. High WPC probabilities for six inches are across the Sierra Nevada, Great Basin, and central Rockies in the Day 1.5 period. The next low approaches the northern CA coast Saturday with the focus of snow in the Trinity Alps where snow elevations around 2000ft and influx of half inch PW allows moderate Day 3 probabilities for six inches. ...Central Plains into Ohio Valley and the Mid-Atlantic... Days 1-2... A relatively weak shortwave trough shifting east across the central Plains and a low level baroclinic zone with an associated band of moderate snow from NE across northern MO will gradually diminish as the wave crosses the ridge over the central CONUS today. Generally less than four inches is expected with this feature across the Midwest today and northern portions of the central Mid-Atlantic tonight. The Allegheny mountains have moderate Day 1.5 probabilities for four inches given the topographic enhancement there. ...Lee of the Rockies to the Upper Midwest and Northeast... A CO low develops as a southern stream trough crosses the central/southern Rockies Friday evening. Potential phasing with northern stream energy from the Canadian Prairies Saturday would create a powerful low over the central Plains. Timing of this phasing and mid-level closing makes for timing uncertainty in the 00Z consensus. The slower 00Z ECMWF is preferred to the faster 00Z GFS though the timing for Day 3 was closer than the 12Z runs. An elongated axis of deformation is likely to develop as the surface low moves northeast across IA Saturday as the upper trough stretches back to the Dakotas. Based on the 00Z consensus and WPC QPF, the greatest chance for heavy snowfall will extend from northern Nebraska and across South Dakota then across southern Minnesota and central Wisconsin. A continued area of concern is where the transition from liquid precipitation to solid precipitation occurs, especially on the eastern side of the system and when cold air advection allows a change from liquid to solid precipitation. The area from northern Iowa/southern Minnesota into the eastern Dakotas looks to have the best chance for moderate to heavy precipitation with lesser concern over precipitation-type. Of additional concern will be the potential for strong surface winds to develop in the wake of the low, resulting in snow/blowing snow capable of significantly reducing visibility. A stripe of freezing rain can be expected just south of the snow transition line currently indicated by low probabilities for a tenth inch accretion over eastern NE on Day 2 and east from IA on Day 3. The warm front from the current system going through the center of the country lifts north with the weekend system bringing a snow risk to upstate NY into New England by Sunday morning. As of now there are low Day 3 probabilities for four inches over northern NY and western New England with moderate probabilities for a tenth inch of ice accretion over northeast PA. Jackson