Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 358 PM EST Mon Feb 21 2022 Valid 00Z Tue Feb 22 2022 - 00Z Fri Feb 25 2022 ...Northern Plains through the Great Lakes and far Northern New England... Days 1-2... Deep troughing digging over The West will direct a leading shortwave trough that ejects northeast from the Four Corners tonight. The associated surface wave currently over the southern High Plains will track northeast across the Midwest to Lake Huron Tuesday. Right entrance jet dynamics from the leading polar jet continue to allow banding over the northern Plains to Lake Superior this evening with the 12Z HREF indicating a drop in the heavier snow bands (over 1"/hr) around 02Z. Only a brief lull in precip/snow will occur up there between this jet and the surface low on Tuesday. Comma head snow then persists along a similar axis over Lake Superior into Tuesday night. Day 1 snow probabilities for 6 or more inches depict the two snow axes well with moderate probabilities from far northeast SD to Duluth with a southern swath over southern MN through northern WI with the highest probabilities over WI/U.P. of MI shoreline with lake enhancement. A warm nose ahead of the surface low will produce some mixed precip of freezing rain and sleet across WI and the northern L.P of MI. Although precip may be generally light, surface wet bulbs temps in the mid to upper 20s and relatively light precip rates could lead to efficient accretion of freezing rain. Day 1 WPC probabilities for freezing rain accretion have further increased with low to moderate probabilities for 0.25" over southern WI and the northern L.P of MI. Finally, as the surface low continues to the northeast over the St. Lawrence Tuesday night, clipping northern Maine early, moderate snow and light icing are likely into Northern New England. Day 1.5 WPC probabilities for 4+ inches of snow are now limited to 50 for northern Aroostook Maine, and as high as 30% for 0.1" of ice in the White Mountains of NH/Maine. ...Western U.S.... Days 1-2... Widespread precipitation will continue to generally shift south across much of the Western United States through Wednesday as a large trough, currently over the OR Coast, digs to the Desert SW. As this trough sharpens and deepens, a surface cold front will dig across the region causing snow levels to plummet to the surface, while also driving enhanced instability through steepening lapse rates beneath the associated cold pool. This setup will produce waves of moderate to heavy snow across nearly the entire West, with a slow southward push of the heaviest accumulations through midweek. Day 1 high probabilities for over 8" are over the northern Sierra Nevada, western CO ranges (particularly the San Juans) with lower probabilities over the highest northern NV/southern UT/northern AZ ranges. The focus shifts southeast to the southern CA ranges, much of terrain in southern UT/central and northern AZ, and much of the CO ranges. The trough ejects east Wednesday night, shifting the precip east of the Rockies. ...Southern Plains and Mid-Mississippi Valley to the Mid-Atlantic... Days 2/3... The large trough digging over the Desert SW through Wednesday with a leading impulse ejecting off Tuesday night before the main trough pushes east of the Four Corners Thursday will send two waves along the a strong baroclinic zone that sets up from a strong cold front moving into over the southern Plains later Tuesday. This will produce an overlap of deep layer ascent through mid-level divergence east of the trough axis, and strong upper jet diffluence in the right entrance region. At the same time, moist advection out of the Gulf of Mexico will become impressive as the LLJ intensifies out of the S/SW, driving robust isentropic ascent at 290-295K atop the surface front. Together, this will produce a quickly expanding area of precipitation from central TX through southeast OK and the Ozarks Wednesday morning and across the Mid-Mississippi and TN Valleys Wednesday night, with freezing rain and sleet becoming widespread as a warm nose surges atop sub-freezing surface temperatures. The key here will be how far south the freezing temperatures extend with CAD for the Ozarks and not much in the way over the MS Delta. The second wave then develops on the intensifying inverted trough ahead of the main trough Thursday. Day 2.5 WPC freezing rain probabilities for 0.25" is 40 to 60% over southeast OK and northwest AR with Day 3 probabilities moderate over southeast MO/southern IL. Lighter precip from the leading impulse allows a swath of Day 3 ice probabilities for over 0.1" to extend along the OH River to the central Appalachians. Jackson Key Messages for Feb 21-22 Winter Storm over the Upper Midwest: - A significant and long duration winter storm will continue to bring snow, sleet, and freezing rain to areas of the Plains and Upper Midwest this evening and expand into the Great Lakes tonight. - Snow will become heavy this evening with rates likely exceeding 1"/hr at times across Minnesota into northern Wisconsin. Near blizzard conditions are possible with considerable blowing and drifting snow. Travel is discouraged. - Total snowfall amounts will likely exceed 6 inches from the Dakotas into the western Great Lakes. More than 12 inches is likely in some areas. - Sleet and freezing rain will overspread the Upper Midwest and Great Lakes through Wednesday morning. Significant ice accumulations of more than one-quarter inch are possible. - Very cold air is expected for much of this week with temperatures near record low values and dangerously cold wind chills in the Plains. Key Messages for Feb 23-25 Winter Storm from southern Plains to Northeast: - A storm is forecast to develop over the southern Plains on Wednesday, move toward the Ohio Valley on Thursday, and then into the Northeast on Friday. Snow, sleet, and freezing rain will be possible. - Freezing rain and sleet are forecast to expand over the southern Plains and Lower Mississippi Valley starting Wednesday and continue into Thursday. Some snow is likely to the north. - As the storm moves into the eastern Great Lakes and Northeast, heavier snow is possible across the northern Mid-Atlantic into New England with mixed precipitation to the south. - Details in the track and timing of the storm in addition to precipitation type and amounts remain uncertain, but will be refined in the next day or so. - Hazardous travel conditions are possible due to the combination of snow, sleet, and freezing rain.