Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 439 PM EDT Sun Mar 14 2021 Valid 00Z Mon Mar 15 2021 - 00Z Thu Mar 18 2021 ...Northern Plains/Midwest... Days 1-2... As the upper low begins to lift northeast from CO across the central Plains, precipitation over the central Plains will shift northeast into the northern Plains and upper Mississippi valley in tandem with an upper level coupled jet, which supports upper divergence maxima and lift crossing southern South Dakota/northern Nebraska tonight and then Iowa/southern Minnesota to Wisconsin Monday. Precip has started out as rain across much of the threat. As the upper low approaches,falling temperatures result in rain changing to snow , with the transition zone moving east roughly in concert with the low. The heavier snows are forecast in the coupled upper divergence/lower convergence maxima across southern SD to southern MN and northern Iowa. WPC PWPF showing high probabilities for accumulations of 4 inches or greater across southeastern South Dakota, southern Minnesota and northern Iowa. As precipitation continues to push farther east, a wintry mix is expected from Iowa into the southern Great Lakes region on Tuesday. While some models are indicating the potential for significant freezing rain accumulations -- resulting in some low end probabilities for ice accumulations of 0.25-inch or more across portions of northern Illinois and Indiana, a mixture of both sleet and freezing rain will likely keep amounts lighter than a quarter inch. ...CA/Great Basin/Central/Southern Rockies/High Plains of southern CO, northeast NM to western KS.... Days 1-3... An upper trough dropping southeast from the Pacific and moving across OR and CA results in a 70 mb front progressing across OR/CA with a period of enhanced moisture/ascent in advance of the front. Strong vertical motions as the pre-frontal band of precip crosses the Shasta/Siskiyou Ranges/CA Cascades and CA Sierra Nevada mountains results in heavy snow across these ranges. The probability of a foot of snow is moderate to high across these CA Ranges. Snow tapers Monday afternoon as the front moves east into NV and drying aloft occurs. Monday night and Tuesday, the 700 mb low moves across southern NV and UT,reaching southern CO/northern NM by Tue evening. Low level convergence and pooled moisture ascent along the low track results in several inches of snow across the ranges along the cyclone's track. The steady movement of the low keep the probabilities of 4 inches low to moderate and probability of 8 inches low in the southern UT Wasatch. On Tue night to Wed., the 700 mb low crosses the Sangre DeCristo Mountains in southeast CO to northeast NM and then turns east northeast across the southern Plains. Several inches of snow are expected in the Sangre de Cristo Mountains as the circulation crosses the region, which should taper late Wed as he low departs. The NAM, ECMWF, Canadian global, and several SREF members show cooling aloft in the north side of the circulation in the Plains of southeast CO to western KS, allowing a change over to snow. There is a chance for several inches of snow according to the ECMWF and SREF mean there. Due to the initial warm temperatures limiting duration of snow, probabilities for heavy snow are limited. Petersen