Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 406 PM EST Mon Mar 02 2020 Valid 00Z Tue Mar 03 2020 - 00Z Fri Mar 06 2020 ...Southern Rockies of New Mexico... Days 1-2... A closed upper low moving shifting southeast down the northwest Mexico coast today will shift east tonight and cross the northern Baja peninsula this evening and northern Mexico through Tuesday night before crossing Texas Wednesday. Ample Pacific moisture flowing into Mexico ahead of the low combines with Gulf of Mexico moisture beginning Tuesday as the low crosses the Sierra Madre Occidental. This low and mid-level moisture below increased upper diffluence and upsloping flow will focus precipitation with snow levels around 7000ft for southern New Mexico. Moderate to heavy snow is expected for the higher mountains of southern NM including the Sacramento Mtns and Black Range where Day 1.5 snow probabilities are moderate to high for 6 or more inches of snow. ...Pacific Northwest and Northern Rockies... Days 1-3... A series of mid-level impulses embedded within confluent flow will continue across southern British Columbia through Tuesday night before the next notable low shifts southeast from the Gulf of Alaska and approaches Vancouver Island Thursday. The impulses will be accompanied by modest height falls and PVA, and at least modestly diffluent flow aloft as a NWly jet streak persists into Washington State through Tuesday night. Although forcing is modest during this time, the prolonged ascent and ample moisture noted by surges of PW more than 1 standard deviation above the climo mean will drive continually repeating rounds of precipitation, with snow levels slowly decreasing from around 5000ft this evening to 3000ft by Wednesday morning. 48hr snow probabilities for Day 1/2 is moderate for 18 or more inches in the highest Cascades and northwest MT ranges. A break in precip is expected after the last impulse and ahead of the larger low Wednesday into Thursday. Precip ahead of that feature arrives Thursday with snow levels in the 3000 to 4000ft range at onset. ...New England... Day 2... A mid-level northern stream trough swinging through the Great Lakes Tuesday into Wednesday will work in tandem with a strengthening jet streak south of New England to become negatively tilted and promote rapid surface cyclogenesis early Wednesday. Latitudinal uncertainty with the track remains with the 12Z global guidance consensus farther north than overnight. The system will be progressive, but strong ascent and moisture advection (PWs to +1-1.5 standard deviations above the climo mean), will support precipitation spreading across New England. A developing TROWAL will shift across northern Maine, while a region of mid-level deformation wraps southeast from Canada. While the column will likely be marginal for snow outside of far northern Maine and higher terrain of northern New England, especially at onset, as the low moves eastward cold air is likely to wrap back into Northern New England, and Day 2 WPC probabilities for 6 inches are moderately high for northern Maine with some low probabilities for the northern Adirondacks and the Green/White Mtns. ...Northern Great Lakes... Day 3... The last mid-level impulse to cross southern BC Tuesday night will amplify as it crosses the northern Rockies and perhaps close off as it reaches the northern Great Lakes Thursday. Most of the Day 3 precip is ahead of the low with marginal temperatures on the southerly flow. Day 3 WPC snow probabilities are 20 to 30 percent for the Arrowhead of MN and the eastern UP. For Days 1-3, the probability of significant icing (0.25-inch or greater) is less than 10 percent. Jackson