Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 259 AM EST Thu Dec 29 2022 Valid 12Z Thu Dec 29 2022 - 12Z Sun Jan 01 2023 ...The West... Days 1-3... Widespread precipitation with areas of heavy amounts, including mountain snow, is expected as a series of shortwaves accompanied by deep moisture impact the region through the remainder of the week into the weekend. A weak shortwave crossing the Northwest later this morning will be quickly followed by a slightly more defined system moving onshore Thursday night into Friday. This is expected to be the wetter of the initial two, with guidance showing the deepest moisture and best forcing positioned across Oregon and Northern California. While orthographically-focused heavy precipitation is expected, rising snow levels will likely keep heavy snow amounts confined primarily to the higher peaks of the Cascades and northern Sierra through Thursday night. For Friday and Friday night, guidance shows another plume of deep moisture spreading inland across California and east into the Great Basin. Heavy precipitation is likely for the Northwest California mountains and the Sierra. However, additional increases in snow levels, rising to 8000-9000 ft across much of California, will limit the threat for widespread heavy snow accumulations on Friday. Low-to-mid level frontogenesis, along with ample moisture spreading east will support widespread precipitation with locally heavy amounts extending across the Great Basin into the Rockies beginning Friday night and continuing into Saturday. Some locally heavy snow accumulations are possible across northern Nevada where snow levels are forecast to hover around 5000-6000 ft. Heavy accumulations are also possible farther north and east across the southern Idaho, western Wyoming, and northern Utah ranges. Additional heavy precipitation is expected across Northern California early Saturday before shifting south into Southern California as an amplifying trough moves onshore. This will bring snow levels lower -- broadening the scope of heavy snow across the Sierra. WPC PWPF indicates accumulations of 8 to 12 inches, with locally heavier amounts, are likely to cover a large portions of the Sierra Saturday into Saturday night. Additional locally accumulations are also possible farther east across the higher elevations of northern and central Nevada into the central Rockies. ...Central Plains & Upper Midwest... Day 1... Guidance continues to show a well-defined shortwave ejecting east from the broad trough in the West, swinging into the central Plains later this morning, before lifting northeast into the mid and upper Mississippi Valley late today. Favorable upper jet forcing along with low-to-mid level frontogenesis will likely support a stripe of light to moderate precipitation shifting northeast across the central Plains this morning. Dynamic cooling encouraging a rapid transition from rain to snow, along with a slight uptick in QPF have helped raise the probabilities for potentially impactful snows across parts of the central Plains. WPC PWPF probabilities for snow accumulations of 2 inches or more have broadened and increased from far northwestern Kansas to the northeastern Nebraska. The latest PWPF now also shows some low probabilities (10-30 percent) for accumulations of 4 inches or more across Nebraska. HREF guidance shows a good signal for banded snowfall, with rates of 1-2 in/hr developing across this area beginning later this morning and continuing into the afternoon. Diminishing forcing is expected to favor lighter amounts farther to the northeast, with WPC PWPF indicating less than inch of snow and some minor icing likely from southwestern Minnesota to the Arrowhead. Pereira