Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 422 AM EST Sat Jan 13 2024 Valid 12Z Sat Jan 13 2024 - 12Z Tue Jan 16 2024 ...Great Lakes and Interior Northeast... Days 1-3... With surface low center shifting northeast over Lake Huron this morning, the event transitions to a prolonged lake effect snow case across all five Lakes by this evening. Strong westerly flow and cold air spreads across the Lakes with lift through the DGZ making for high SLR through tonight, though the powerful winds should temper SLRs a bit with dendritic fracturing and the strong CAA sends low level thermals below the DGZ from west to east Sunday into Monday. Day 1 snow probs for >8" are moderate (40-70%) in westerly snow belts of the U.P., down the length of the western L.P. around Buffalo, NY and in the Tug Hill. Farther to the east, cold air in place over the interior Northeast will continue to retreat today 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. Day 1 PWPF for >6" are limited to the White Mtns of NH into Maine as well as far north Maine. For Day 2, ending 12Z Monday, single band LES on Lakes Erie and Ontario rule with moderate to high probs for >8". Low probs for >4" are over the U.P. and western L.P with the aforementioned sub DGZ air spreading in limiting snowfall. as 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. Sunday into Monday, as the low retrogrades from Quebec to the Hudson Bay, the heavy lake effect potential is expected to diminish as winds become more west-southwesterly across the Lakes with single bands continuing over the eastern Lakes and multi-bands over the Keweenaw Peninsula and portions of the western L.P. where Day 3 PWPF for >4" are low to moderate. ...Western U.S.... Days 1-3... A compact southern stream low will reaching the Oregon Coast today. A preceding conveyor belt of subtropical moisture shifting ahead of the low and across OR/northern CA across the northern Great Basin through the Wasatch of UT and the CO Rockies with continued heavy snowfall over 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 with Day 1 PWPF for >12" moderate to high across all these ranges the Cascades/Sierra Nevada east through the Wasatch. As this plume comes ashore, warm air riding over the arctic-sourced surface air will cause significant freezing rain north of the stationary front for west-central and northwest Oregon into southwest WA through this evening. Day 1 PWPF for >0.25" ice is 40-80% for the southern/central Willamette Valley and northern OR Coast Ranges to the coast/sea level. Ridging begins to shift across the West Coast Sunday morning, with precipitation shunting east. Day 2 PWPF for >8" is moderate to high for the Wasatch and CO Rockies. A longwave trough axis shifting down the High Plains Monday maintains a focus for snow over CO with Day 3 PWPF for >6" moderate over the central/northern CO Rockies. ...Mid-South/TN Valley/southern Appalachians... Days 2/3... Compact southern stream mid-level low approaching OR today opens into a shortwave trough over the Great Basin tonight as it and a following impulse swiftly dive southeastward across the southern Rockies Sunday and around the base of the longwave trough spanning the CONUS shifting from North Texas to the southern Appalachians Sunday night through Monday night. These impulses will allow waves of generally light precip over the southern Plains/Mid-South Sunday afternoon and night. A reinforcing axis to the longwave trough shifts down the Plains Monday, further promoting Mid-South through TN precip development as further Gulf moisture surges north over the Arctic-sourced airmass in place (cold front reaches the Gulf Coast by early Sunday). Sunday afternoon through night, generally light to locally moderate snow will expand eastward across eastern OK and through AR and into TN with some wintry mix over northeast TX and northern LA. However, the approaching trough axis, with it's strengthening Wly jet positioned to give the Mid-South through TN right entrance jet upward motion on Monday ramps up precip with moderate to locally heavy snow bands setting up. 00Z global guidance is pretty consistent with a swath of snow from central AR through TN where Day 2.5 WPC snow probabilities for at least 4 inches are moderate (40-60%). Farther south, cold surface temperatures beneath a warm nose aloft supports an area of freezing rain/sleet from the TX Hill Country eastward across northern LA where Day 2.5 ice probs are moderate (20-60%) for more than 0.10" ice. The depth of cold air should allow some sleet, particularly north toward the snow areas, so please stay tuned to future updates on ptype info on this southern side of the precip shield. Jackson ***Key Messages for Jan 10-14 Midwest Winter Storm Becoming Lake Effect*** --Blizzard Conditions, Hazardous Travel Continues Heavy snow will continue to diminish this morning. However strong winds and light snow will still cause areas of reduced visibility. Ground blizzard conditions are possible over portions of Nebraska, South Dakota, Minnesota and Iowa where strong winds will blow the recently accumulated snowfall. Travel will remain dangerous over portions of the area. --Potent Lake Effect Snow through Sunday-- Cold air surges over the Great Lakes in the wake of the low today, generating heavy lake effect bands downwind of all Great Lakes through Sunday with more localized/moderate banding then continuing through midweek. Whiteout conditions from the powerful winds in the heavy lake effect snow bands are expected. An additional 8-12 inches are expected in Michigan snow belts and two or more feet of snow in west wind snow belts off Lakes Erie and Ontario are anticipated through Monday night. --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 Northeast today will lead to renewed rises on rivers and streams and possible flooding. Moderate to isolated major coastal flooding is forecast in the Mid-Atlantic and Northeast today, 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 will 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. Significant freezing rain is expected today 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 the Tennessee Valley Sunday into Monday. Several inches of snow are possible. --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.