Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 405 PM EST Thu Mar 07 2019 Valid 00Z Fri Mar 08 2019 - 00Z Mon Mar 11 2019 ...Western United States... Days 1-3... A closed/cutoff low initially located over the Salish Sea over the BC/WA will continue to drift eastward across the northern Rockies through Saturday as the system opens up. A southern stream mid-level ridge axis over the CA coast has cutoff Pacific moisture inflow across the Great Basin with precip rates decreasing...at least temporarily. However, the next southern stream shortwave trough reaches the central CA coast later tonight which will bring a return of Pacific moisture along with a strong jet moving zonally across southern CA allows snow elevations to drop. The next low approaches the northern CA coast Saturday with the focus of snow in the Trinity Alps where snow elevations around 2000ft. Snow will spread inland into portions of the central Great Basin. ...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 light to moderate snow extended from Iowa southeastward into the southern portion of West Virginia. The models point to generally light snowfall amounts along this axis and in the upslope region of the Appalachians where lift will be aided by the low level orographics. ...Lee of the Rockies to the Upper Midwest and Northeast... Surface low pressure will be developing to the lee of the Colorado Rockies and front range as a southern stream trough crosses the central/southern Rockies Friday evening. Deepening will ensue on Saturday. Our preference was non NAM which seemed to eject shortwave energy out too quickly while the UKMET was more inclined to be too slow because of interactions between this shortwave and the trough over Alberta and Saskatchewan which grazes the international border region. The ECMWF and GFS were largely in the middle of the spread and were largely used...with somewhat more preference given to the ECMWF for timing but attempted to account for it tending to be a warmer piece of guidance. The greatest chance for heavy snowfall still looks like it will extend from northern Nebraska and across much of South Dakota then across southern Minnesota and central/northern 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 on the western side of the system. 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 Nebraska on Day 1 and east from Iowa into Wisconsin on Day 2. Bann