Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 445 PM EST Mon Jan 25 2021 Valid 00Z Tue Jan 26 2021 - 00Z Fri Jan 29 2021 ...Central Plains to the Northeast and Mid-Atlantic... Days 1-2... Ongoing moderate to heavy snow centered across eastern Nebraska and Iowa is expected to diminish during the evening into the overnight hours as the favorable forcing gradually wanes. However, hi-res guidance indicates that banded snow, producing snowfall rates of 0.5 in/hr, may persist for a few hours across Iowa into northern Illinois and far southern Wisconsin early in the period -- promoting high probabilities for additional snow accumulations of 4-inches or more. Easterly to northeasterly flow developing early across southern Lake Michigan and continuing through the overnight into early Tuesday is expected to support lake-enhanced heavy totals along the southwestern lakeshores. Meanwhile, moisture spreading north along a low-to-mid level baroclinic zone lifting across the Appalachians and Mid-Atlantic, will encounter a wedge of cold air to the north -- setting the stage for snow, followed by a wintry mix across the central Appalachians and Mid Atlantic. While there remains a strong signal for significant ice accumulations across portions of western Virginia, the Eastern West Virginia Panhandle, western Maryland and western Pennsylvania, probabilities for at least measurable snow have increased farther east, with the 12Z NAM and hi-res model suite indicating a period of moderate snow developing this evening before changing over to mixed precipitation across the I-95 corridor into the Delmarva. As the the low-to-mid level frontal band continues to translate northward, axis of heavier, organized precipitation is forecast to lift through the northern Mid-Atlantic into the Northeast on Tuesday, with thermal profiles supporting mostly snow across Upstate New York and New England. Models show a period of strong southwesterly-southerly flow/frontogenesis ahead of the approaching low level center supporting a period of heavier snowfall developing across Upstate New York into western New England, with some orographically enhanced totals from the southern Adirondacks into the southern Green and Berkshire mountains on Tuesday. ...Southwest... Day 1... A deep upper trough/developing closed low moving across Southern California into the Southwest is expected to produce widespread high elevation snow across the region through Monday night into Tuesday across the region. This includes areas along the Mogollon Rim into the mountains of southeastern Arizona and southwestern New Mexico -- where widespread totals exceeding 8-inches are expected. Locally heavy totals are also forecast for the mountains of southern Nevada and southern Utah. ...Western U.S.... Days 2-3... Beginning Tuesday and continuing through the remainder of the period, a major winter storm is expected to produce widespread snow across portions of the Northwest, the northern Rockies and California, with multiple feet likely across the Sierra and mountains of Northern California. Heavy snows are expected to develop across the mountains of Northern California as a deep low dropping south from the Gulf of Alaska approaches the coast late Tuesday. While the heaviest amounts are expected to fall across the higher elevations of the Klamath mountains into the southern Cascades, snow levels are expected begin low, supporting accumulating snows near the coast. Although the initial low is expected to weaken off the coast, energy digging south into the base of the trough is expected to amplifying the trough -- focusing the strongest inflow farther to the south, with heavy snows moving south along the Sierra Tuesday night into Wednesday. Heavy snows will likely continue along the central and southern Sierra through Thursday as the upper trough slowly pivots east. Pereira