Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 341 PM EST Tue Jan 31 2023 Valid 00Z Wed Feb 01 2023 - 00Z Sat Feb 04 2023 ...Significant and long-duration ice storm from the Southern Plains through the Mid-South through Wednesday night... ...West-Central Texas through the Mid-South... Days 1-3... A highly anomalous, positively tilted upper trough over Baja will work in tandem with a strong upper ridge over the Gulf of Mexico to channel a plume of rich subtropical moisture into the Southern Plains and into the Mid-South. NAEFS depicts >99th climatological percentile values for the IVT over northern Mexico this evening. By Wednesday afternoon, IVT of ~500 kg/m/s will be places over southeast TX while the available moisture aloft has origins stemming from the tropical East Pacific. This stream of anomalous moisture content will be embedded within strong 850-300mb mean layer winds aloft. Meanwhile, below 850mb, temperatures are below freezing from the Davis Mountains of West Texas, on south to the San Antonio/Austin metro areas, and all the way east to the Mid-South. Sub-freezing temperatures here are reinforced by the presence of a cold high pressure system over the Middle MS Valley aiding in keeping a sufficiently cold air-mass in place to create wintry precipitation. The strong WAA aloft will result in a burgeoning warm nose with >0C temps aloft, causing frozen precipitation aloft to melt, then either refreeze as sleet of hit the ground as freezing rain. The strong vertical ascent aloft, prolonged supply of rich atmospheric moisture, and cold air damming setup in place is a recipe for a significant ice storm that will continue to unfold tonight across the Southern Plains and into portions of the Mid-South through Wednesday night. Overall, most CAMs have done a better job capturing the footprint of subfreezing temperatures. This has led to this forecast cycle relying heavily on the HREF tonight and into early Thursday morning. Latest WPC PWPF shows the greatest probabilities (60-80%) for >0.25" of ice accumulation are over TX's Edwards Plateau, the Concho Valley, and into north-central Texas. It is worth noting, particularly farther west into the Permian Basin and north to the Red River Valley, that the depth of the cold wedge will be deeper, and thus sleet will be the primary precipitation type. Regardless of p-type, the combination of freezing rain and sleet will cause dangerous travel conditions from TX to the Mid-South. The WSSI continues to show a large swath of Moderate Impacts throughout much of central TX, central AR, northwest MS, and southwest TN. These impacts are solely driven by the Ice Accumulation algorithm in the WSSI. Bridges and overpasses are the most prone areas to icing with the potential for downed trees and power lines resulting in scattered power outages. ...Great Lakes... Day 1-3... A fast moving upper level disturbance rounding the base of a deep upper low over Hudson Bay will cause an increase in low level westerlies, which is set to cause lake effect snow bands to produce snow along the northern coast of Michigan's U.P., over western Michigan, and downwind of Lakes Eire and Ontario. Day 1 WPC PWPF identified the Tug Hill as the area most likely area to see >6" of snowfall, with probabilities >90%. In fact, the highest elevations of the Tug Hill could pickup over 12" of snowfall tonight and into Wednesday night. By Thursday afternoon a powerful Arctic front will race across the northern Great Lakes, prompting lake effect snow bands to form first off of Lake Superior, then the other Great Lakes by Thursday night. Winds will generally be out of the NW, which will make Huron and Michigan the Great Lakes with the best odds of producing lake effect snow bands. There is also the potential for snow squalls along the front as it traverses the Northeast late Thursday night and into Friday morning which could result in reduced visibilites. Mullinax ...Key Messages for Jan 30-Feb 1 Southern Plains to Mid-South Ice Storm... --Several more rounds of freezing rain, mixing with sleet at times, are expected through Wednesday night. --Additional ice accumulations of a quarter to half inch are forecast over much of West, Central, and North Texas. An additional tenth to quarter inch of ice is forecast over southern Oklahoma, south-central Arkansas, and east through the greater Memphis metro area. --Accumulating ice on roadways, especially bridges and overpasses, will cause treacherous travel conditions. --Prolonged power outages and tree damage are likely.