Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 328 AM EST Wed Mar 03 2021 Valid 12Z Wed Mar 03 2021 - 12Z Sat Mar 06 2021 ...Four Corners... Days 1-2... A mid-level closed low emerging from Southern California this evening will move eastward across the Four Corners Thursday before ejecting into the Southern Plains on Friday. Enhanced mid-level divergence, height falls, a LFQ jet streak divergence maxima, and intensifying southerly WAA will combine to produce moderate to heavy snow in the terrain of the Four Corners mountains this evening and Thursday. Snow levels are expected to climb as high as 6000-8000 ft during the heaviest precip, confining the significant snow to these elevations. The heaviest snow through Thursday is likely to be in the San Juans which will benefit from upslope enhancement due to the orthogonal southerly flow, and WPC probabilities are high for 6 inches each of the two days. Otherwise, WPC probabilities are moderate for 6 inches on D1 in the southern Wasatch, extending into most of the CO Rockies on D2. Lighter snows accumulating to a few inches are likely D2 across the Palmer Divide. ...Pacific Northwest... Days 2-3... A closed mid-level low is likely to move slowly west of the coast Thursday and Friday, with pronounced southerly 700-500mb flow drawing tropically sourced moisture northward along the coast of northern CA and into WA/OR. As the low slowly migrates eastward, a surface cold front will move onshore, but not until late D3 /Friday evening/, which will finally bring a slow wane to the precipitation. However, a prolonged period of warm/moist advection ahead of this front will drive significant precipitation across the Coastal Ranges and into the WA/OR Cascades. Snow levels will rise on this warm flow, and are expected to generally be above 4000 ft in WA/OR, before falling to 2500-3000 ft on D3. WPC probabilities D2 are high for 6 inches in the Olympics, where isolated totals approaching 2 ft are possible. By D3, there will be enough of an eastward push in the flow to drive heavy snow across the northern Sierra, Siskiyous/Shastas/Trinities, and into the OR/WA Cascades, as well as continuing in the Olympics. WPC probabilities are moderate to high for 6 inches in these ranges, with local maxima above 12" likely. For Days 1-3, the probability of significant icing (0.25 inch or greater) is less than 10 percent. Weiss