Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 335 AM EST Sat Dec 31 2022 Valid 12Z Sat Dec 31 2022 - 12Z Tue Jan 03 2023 ...Western U.S.... Days 1-3... A plume of deep moisture, directed by an amplifying shortwave, will gradually move south across California today. This will support widespread precipitation with heavy amounts expected along the favored terrain. Snow levels which are initially quite high, are expected to steadily fall as the system moves onshore later today. Heavy snow is likely for the Sierra, with multiple feet expected, especially along the central to southern Sierra, before precipitation begins to wane early Sunday. Meanwhile ample moisture spilling east is expected to interact with a lingering frontal zone and favorable upper jet forcing to support locally heavy precipitation, including mountain snow, across northern Nevada, northern Utah, southern Idaho, and western Wyoming. For Sunday and Sunday night, guidance shows the aforementioned shortwave continuing to amplify as it moves east of California into the interior West, with a closed low developing early Monday near the Four Corners region. This will the potential for heavy snow farther south and west, including the Arizona High Country and mountains. Additional heavy snow is also expected for the Utah and western Colorado ranges. This includes the San Juans and Uintas, where additional accumulations of a foot or more likely. Farther to the north, a low-to-mid level baroclinic zone lifting north, along with increasing easterly flow will support widespread precipitation, including areas of heavy snow, developing across Wyoming, including areas east of the Divide. Several inches can be expected across many of the south-central to central Wyoming ranges, with a foot or more likely along the Wind River Range. On Monday, the system is expected to move across the central Rockies into the Plains. Additional heavy accumulations are possible along the western edge of deformation zone extending from the High Plains back into the Front Range as the system begins to depart on Monday. Meanwhile back to the west, shortwave ridging and dry conditions along the West Coast late Sunday into Monday will give way to the next approaching system -- a relatively drier system that it is expected to bring at least a few inches of snow to the Northwest California mountains and the Sierra late Monday into early Tuesday. ...Central Plains... Day 3... As the system in the West moves east of the Rockies into the High Plains, there remains a good signal for banded heavy snow developing within the associated deformation zone. South of the axis of heavier snow, a wintry mix including some potential for significant icing is expected. However, confidence in the placement of heavier amounts remains low, especially east of the High Plains as the models continue to diverge on the track and amplitude of the system. The GFS and its ensemble members continue to remain north of much of the non-NCEP guidance. Probabilities for accumulations of 6 inches or more remain highest across the Nebraska Panhandle to south-central South Dakota, with probabilities dropping off significantly farther east with the increasing model spread. Pereira ...Key Messages for January 1-3 Winter Storm... -- A strong winter storm moving out of the Rockies late this weekend will bring a wintry mix of snow, sleet, and freezing rain to the Central and Northern Plains late Sunday into Tuesday. -- Snow will overspread much of the area late Sunday into Monday. Moderate to heavy snow along with some blowing snow will make for difficult travel. -- An area of sleet and freezing rain is possible across portions of eastern Nebraska and South Dakota into Iowa. --Heavy snow is likely into the Upper Midwest through late Tuesday, though there remains some uncertainty in the storm track and which areas will receive the heaviest snow.