Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 543 PM EST Fri Jan 12 2024 Valid 00Z Sat Jan 13 2024 - 00Z Tue Jan 16 2024 ...Great Lakes and Interior Northeast... Days 1-3... A powerful storm now centered over the mid Mississippi Valley will intensify further as it continues to lift northeast, with the model consensus showing a consolidated surface low dropping into the mid to upper 970s as it tracks across southeast Lower Michigan into Lake Huron overnight. Heavy synoptically-driven snow on the the northwest side of the low will continue to translate north across northern Lower Michigan during the evening. Lake enhanced snow over the upper Great Lakes will transition to intense lake effect that will develop across all the Great Lakes by late Saturday as the low lifts into Quebec and much colder air begins to sweep across the still relatively-warm lakes. Further to the east, cold air in place over the interior Northeast will retreat in the face of southerly flow ahead of the low's advancing cold front. Snow at the onset will transition to a wintry mix before changing over to all rain in many locations as the cold air erodes. For Day 1, ending 00Z Sunday, WPC PWPF shows high probabilities (greater than 70 percent) for additional snow accumulations of 8 in or more across northern Lower Michigan and in the Upper Michigan snow belts. Within this area, the PWPF shows high probabilities for accumulations of a foot or more, with the highest in the Huron Mountains, where north to northwest flow is expected to accentuate totals. In the Northeast, heavy snow amounts are expected to be more localized, with the higher probabilities for accumulations of 4 inches or more confined mainly to the Adirondacks and the northern New England mountains from the Greens to northern Maine. For Day 2, ending 00Z Monday, as strong westerly flow and cold air spreads across the lower Lakes, the probabilities for locally heavy snow develop in the Buffalo Metro area and near and north of the Tug Hill region. The WPC PWPF shows high probabilities for amounts exceeding 8 inches in these areas. Then on Day 3, ending 00Z Tuesday, as the low tracks farther to the north and then backs to the west over Hudson Bay, the heavy lake effect potential is expected to diminish as winds become more west-southwesterly across the Lakes. ...Western U.S.... Days 1-3... An active wintry pattern will continue into the weekend from the southern Cascades and the Sierra, through much of the Great Basin to the Colorado Rockies along an arctic boundary dropping into the region. A rich plume of 850-700mb moisture running along this boundary, along with topographic lift will allow heavy snow to continue over the Oregon Cascades, across southern Idaho, northern Utah and the Wasatch, to the Colorado Rockies. Strong winds are expected in this tight baroclinic zone, with blizzard warnings in southern Idaho and portions of southwestern Wyoming. Meanwhile a compact southern stream low will cut through the North Pacific/Alaska ridge tonight, reaching the Oregon Coast late Saturday. This storm system will tap into a conveyor belt of subtropical moisture. This will bring further heavy snowfall into the Oregon Cascades with the footprint expanding south through the Sierra Nevada. Confidence is highest in heavy snowfall accumulations along the stationary front from southern Oregon and northern Nevada to the Wasatch, which is at the nose of the strong IVT plume emanating out from the northeast Pacific. As this wave comes ashore, warm air riding over the arctic air at the surface will set up a significant freezing rain case for northwest Oregon into southwest WA. Ridging begins to shift east into the West on Sunday, with precipitation shifting east. For Day 1, ending 00Z Sunday, WPC PWPF shows high probabilities (greater than 70 percent) for snow accumulations of 8 in or more for portions of the southern Cascades and northern Sierra, southeast Oregon, southwest Idaho, northern Nevada, and northern Utah. Ice accumulations of 0.1 inch or more are likely across portions of northwest Oregon. For Day 2, ending 00Z Monday, WPC PWPF shows addition snow accumulations of 8 inches or more are possible across portions of the same previously highlighted areas, but most likely along the northern Utah ranges and along the south-central Wyoming and western Colorado ranges. For Day 3, ending 00Z Tuesday, snow is expected to end west of the Great Basin as the upper ridge builds, however additional accumulations are likely for the northern Utah, and the southern Wyoming and western Colorado ranges. ...Mid-South/Lower MS Valley/eastern TX... Day 3... Sharp trough/splitting shortwave over the northern/northeastern Pacific this evening will swiftly dive southeastward and move through the Southwest/Four Corners Sunday. Thereafter into day 3, strengthening upper jet across the Mid-South will support an expanding area of snowfall over the southern Plains Sunday night into Monday in the right entrance region. Surface cold front will have plunged to the Gulf Coast, allowing cold arctic air to invade the region as Gulf moisture returns on southerly flow at 850mb. Through Monday, snow will expand eastward across eastern OK and through AR but also southward over southeastern TX. In the deeper cold air, generally north of I-20, frontogenetic banding may enhance some totals over AR, but models differ on placement. Formed a consensus with a nudge toward the wetter, but not wettest, side of the QPF, resulting in an area of >4" over a broad region. WPC probabilities for at least 2 inches of snow are moderate (40-70%) from eastern OK eastward to middle TN, and northward to southern MO/KY and southward to around the ArkLaTex eastward to northern MS. Within this area, WPC probabilities for at least 4 inches are moderate (40-70%) across central AR eastward to western TN (including northwestern MS) through 00Z/16 (Monday evening) with the event continuing thereafter. Farther south and southwest, cold surface temperatures beneath a warm nose aloft supports an area of freezing rain from the TX Hill Country eastward across northern LA and southern AR into western MS. Ensemble ptype guidance shows some probabilities of all four types but with a dominant signal for ice vs sleet (though each or both are quite possible), though the models always struggle with near-surface sub-freezing layers and the evolution of the warm nose. Overlap of the higher ZR probs and higher QPF (closer to the TX/LA border) may result in more significant icing. As of now, WPC probabilities for at least 0.10" ice are low (generally 10-40%) from near I-35 near AUS east-northeastward into northern LA along and south of I-20. Again, uncertainty in both ptype and QPF amounts will likely make for a changeable forecast for at least the next day or so. The probability of any icing exists from the Hill Country eastward through the I-10 corridor, northeastward to northern AL. Fracasso/Pereira/Jackson ***Key Messages for Jan 10-14 Major Winter Storm over the Midwest*** --Blizzard Conditions, Hazardous Travel Continues-- Heavy snow and 25-40 mph wind gusts are creating blizzard conditions, especially from eastern Nebraska through Iowa and parts of Wisconsin. 1 to 2 inch per hour snow rates have also been observed. Travel is dangerous to impossible, and whiteout conditions will continue in several areas through Saturday. Power outages could also occur. --Lake Effect Snow Persists This Weekend-- While the larger snow area will diminish on Saturday, the arrival of colder air will generate heavy snow downwind of the Great Lakes this weekend into midweek. Whiteout conditions in the lake effect snow bands are expected, and an additional 12-24 inches of snow will occur through Monday across much of Michigan and western through northern New York State. --Flooding & Severe Storms in the South and East-- Severe storms remain possible in the South today and damaging gusts may occur outside of thunderstorms. Heavy rain in the Mid-Atlantic and Northeast Friday night and Saturday will lead to renewed rises on rivers and streams and possible flooding. Moderate to isolated major coastal flooding is likely in the Mid-Atlantic and Northeast Saturday, with significant impacts. ***Key Messages for mid-January Arctic Blast*** --Dangerously Cold Wind Chills Expected-- Sub-zero wind chills will affect much of the U.S. and reach into portions of the South. Wind chills this weekend will fall below minus 30 degrees from the northern Rockies to northern Kansas and into Iowa. Values may drop as low as minus 50 degrees from Montana across the western Dakotas. These wind chills will pose a risk of frostbite on exposed skin and hypothermia. Have a cold survival kit if you must travel. --Snow from West Coast to Rockies, Ice in Oregon-- Heavy snow, blowing snow, and valley icing will all contribute to poor to impossible travel from Oregon, Idaho, Nevada, and Utah, including the Portland, Boise, and Salt Lake City metro areas. Freezing rain is likely Saturday over western Oregon with tree and powerline damage possible. --Wintry Precipitation into Mid-South by Late Sunday-- Areas of snow, sleet, and freezing rain are likely to develop and spread across parts of eastern Oklahoma and the ArkLaTex through late Sunday. A few inches of snow will be possible across these areas by Monday. --Hazardous Cold Weather to Persist/Re-develop-- Parts of the Midwest could again experience near record, dangerously low temperatures and wind chills, with subfreezing temperatures again possible in the Deep South by late next week.