Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 346 PM EST Wed Feb 16 2022 Valid 00Z Thu Feb 17 2022 - 00Z Sun Feb 20 2022 ...Rockies... Day 1... An upper low in the southern stream will will continue to transition to an open wave and eject eastward across the Southwest this evening ahead of a northern stream trough digging through the Intermountain West into the Four Corners region. As the low advances across the Southwest, generally light snows are expected along the Mogollon Rim into the eastern Arizona and western New Mexico mountains. However some locally heavier amounts are possible, especially cross the White Mountains in eastern Arizona, where high probabilities for accumulations of 6 inches or more are centered. Meanwhile, the amplifying northern stream trough along with upslope flow on the backside of a backdoor front will support snows advancing south through the central and southern Rockies. While widespread heavy accumulations are not expected, WPC probabilities do indicate significant potential for accumulations of 4 inches or more along and east of the Colorado Front Range, including the Denver Metro, and for areas farther south into the San Juan, Sangre de Cristo, and Jemez mountains. ...South-central Plains to the Northeast... Days 1-2... The previously noted southern stream shortwave is forecast to eject into the southern Plains overnight as a negatively tilted trough over the Central Plains. This will support the rapid development of a surface cyclone over the Texas Panhandle and Oklahoma that is expected to quickly track to the northeast, reaching the Northeast and New England by Friday morning. Moisture ahead of this system is impressive, with PW anomalies nearing +2 sigma and the deepening low and tightening baroclinicity will result in a narrow but intense area of frontogenesis Thursday. This lift lies within the DGZ, which should promote very intense snow rates within the deformation band northwest of the low track. The most recent HREF continues to show a strong signal for up to 2"+/hr rates. Combined with the tightening pressure gradient, significant blowing snow will be possible. It remains likely that a quick hitting, but very intense snow will setup across portions of Kansas through Illinois, northwest Indiana, and southern Michigan. While the 12Z guidance shifted slightly south, WPC probabilities indicate accumulations of 4 inches or more are very likely (greater than 70 percent) along a narrow axis stretching from south-central Kansas to southern Lower Michigan. This includes the KC, southern portions of the Chicago, and the Detroit metros. Along this axis, locally heavier amounts are likely, with WPC probabilities indicating amounts of 8 inches are a significant possibility. To the south of the heavy snow, a stripe of freezing rain is expected as a warm nose aloft overruns subfreezing temperatures at the surface. While widespread heavy ice accumulations are not expected, WPC probabilities do indicate significant potential for localized accumulations of 0.10 inch or more from portions of the mid Mississippi Valley to the lower Great Lakes region. As the low moves across the Northeast Thursday night, with the exception of northern Maine, the rain/frozen precipitation line is expected to linger near the U.S./Canada border. Expect any significant snow accumulations to remain largely confined to northern Aroostook County in Maine. ...Upper Midwest to Great Lakes... Days 2-3... Models show a shortwave diving quickly southeast across central Canada, reaching the Upper Midwest by Friday morning. This quick moving clipper system is then expected to track through the Great Lakes Friday into Friday night. Ample cold air pulled southeastward into the region in the wake of the aforementioned storm system combined with modest forcing for ascent within the left exit region of the 130+ kt jet should yield a few fluffy inches of snow. As the shortwave passes, some lake effect snows are likely to develop from west to east, with WPC probabilities indicating local amounts of 4 inches or more are likely in some of the snow belt regions, including the U.P. of Michigan the Tug Hill. Pereira Key Messages for the Feb 17-18 Winter Storm: - A strong winter storm will impact the Central U.S. from late tonight into Thursday night, producing wintry hazards of heavy snow, sleet, and freezing rain. - A swath of heavy, wet snow is expected over northern Oklahoma, eastern Kansas, northern Missouri, north-central Illinois, northwest Indiana, and southern Michigan. Snowfall rates are likely to exceed 2 inches per hour at times. - The combination of heavy snow and strong, gusty winds will lead to severely reduced visibility and hazardous travel conditions Thursday into Thursday Night. - Swaths of locally heavy freezing rain and sleet are likely just to the south of the heavy snow swath, over central Missouri and Illinois, north-central Indiana and northern Ohio. Impacts to travel are likely in these areas as well.