Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 333 PM EST Sun Nov 08 2020 Valid 00Z Mon Nov 09 2020 - 00Z Thu Nov 12 2020 ...Montana... Day 1... ...Blizzard continues into tonight... A 990mb surface low over northwest ND will lift into Manitoba this evening as a TROWAL under the closed H5 low over northeastern MT continues to bring moderate to locally heavy snow across northeastern MT this afternoon. This setup, combined with the 1030mb surface high over northern BC/Alberta will keep snow falling and the wind blow strong over north-central/northeastern MT into tonight. By Monday morning, however, the elongated mid-level trough will have shifted the focus for precipitation to northern Ontario and the surface high building in will allow the winds to ease, thus ending the blizzard. Day 1 WPC snow probabilities for an additional 6 inches after 00Z are moderate over portion of north-central MT. ...Four Corners.... Day 1... A reinforcing closed low now over the northern Sierra Nevada will swing east over the southern Great Basin tonight and eject east across the south-central Rockies and onto the southern High Plains Monday night. Pacific moisture wrapping in south/east of this low and dropping snow levels will produce widespread moderate to heavy snow across the higher terrain (snow levels generally 6000ft now drop to 4000ft tonight) of the Four Corners states into Monday. The heaviest snow is again expected in the San Juans of CO tonight where orthogonal mid-level flow, and instability will enhance precipitation where Day 1 WPC probabilities are high for 12" bringing 36hr snow totals in excess of 3 feet. Elsewhere on Day 1, 6 or more inch probabilities are moderate in AZ (for the Kaibab Plateau, Mogollon Rim, White Mtns), UT (southern and eastern UT ranges and Wasatch), western CO ranges, and and NM part of the San Juans. ...Pacific Northwest and Northern Rockies... Days 2/3... The next shortwave trough digs across WA Monday night and it and a reinforcing trough following close behind and slowly shift east across the northern Rockies into Wednesday. Decent Pacific moisture ahead of the initial trough will make for the highest snow probabilities in the WA Cascades on Day 2 where 6 or more inches are likely with snow levels down around 2000ft. The expanding trough over the Northwest CONUS shifts the snow focus south and east with Day 3 snow probabilities for 6 or more inches moderate for the OR Cascades, OR Blue Mtns, northern ID Mtns (Clearwater and Bitterroots), Lewis Mtns in MT, and high for the Tetons in WY. ...Central Plains to Upper Midwest... Days 2/3... The cold front from the low shifting north from ND this afternoon will slow in its progression east on Monday as the reinforcing low currently over northern CA/NV will eject east across the south-central Rockies Monday night and allow surface low pressure to ride northeast along the baroclinic zone from the central Plains late Monday night to the Upper Midwest Tuesday. A fairly narrow swath of locally moderate snow is expected in the comma head of the developing low from western the western KS/NE border Monday night to southern/central MN through Tuesday. Rapid cyclogenesis Tuesday over WI will allow for the swath to become more intense with additional enhancement from Lake Superior Tuesday evening allowing heavy snow to develop over far northern WI/the Arrowhead of MN before quickly exiting into western Ontario Tuesday night. It should be noted that the GFS remains farther east with its track over the Upper Midwest while the ECMWF/CMC/UKMET are farther west/inclusive of Duluth and are preferred at this time. Day 2.5 snow probabilities for 4 or more inches increase up to 10 percent in south-central MN, but increase to likely from the Duluth area to Grand Marais, MN. Ahead of the developing low, a wintry mix transition zone is expected to develop with low Day 2 probabilities for a tenth inch of ice extending from southeast Neb across northwest IA and over southern MN. Jackson