Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 155 PM EST Fri Mar 7 2025 Valid 00Z Sat Mar 08 2025 - 00Z Tue Mar 11 2025 ...New England... Day 1... Sharp cyclonic flow will persist across New England Friday night and Saturday as an upper low spins across eastern Canada. Within this flow, a shortwave is progged to drop southeast across New England Friday night, pushing a surface trough eastward which will additionally enhance the low-level NW flow. The result of this evolution will be increased upslope ascent into the Greens and Whites, leading to rounds of moderate snowfall through D1. The coverage of snowfall is likely to be modest and confined to the highest elevations, but WPC probabilities indicate a 50-70% chance for 4+ inches of snow in northern VT and near the Presidential Range of NH before precip winds down before D2. ...Four Corners States through Oklahoma/Texas Panhandles... Day 1... Strong closed mid-level low characterized by 500mb heights falling below the 2.5 percentile of the CFSR database will move eastward slowly across AZ/NM tonight, before slowly beginning to fill over the TX/OK Panhandles Saturday. Downstream of this closed low, an upper jet streak will amplify across the Southern Plains, reaching 150 kts while emerging meridionally from near Baja. Together, these features will produce strong deep layer ascent into the Southern Rockies. At the same time, moisture being advected into the column will be impressive as both low-level moisture through S/SE flow into the system, and upper level moisture on SW isentropic ascent combine across the region, angling elevated PWs into the southern High Plains. The overlap of this deep layer lift and increasing moisture will result in an axis of moderate to heavy precipitation across NM and into the OK/TX Panhandles, with low-level easterly flow on Saturday contributing enhanced upslope ascent into the Sangre de Cristos and along the Raton Mesa. In general, snow levels will be 5000-6000 ft, but will crash through D1 to as low as 4000 ft before precip wanes by early D2, but before this occurs heavy snow is likely across the White Mountains of AZ and especially into the Sangre de Cristos and along the Raton Mesa where WPC probabilities are high (>70%) for 12+ inches of snow. Farther east into the Panhandles of TX/OK, the column is marginally conducive for wintry precipitation. However, strong ascent through both synoptic and mesoscale forcing could cause periods of dynamic cooling sufficient to bring snow to the surface. This is most likely across the TX Panhandle as reflected by HREF 1"/hr snow rate probabilities. The most likely timing for this heavy snow is during the afternoon hours which will also limit accumulations, but where dynamic cooling is strong enough and snow can persist, some locally moderate snowfall accumulations of 2-4" are possible (30-50% chance). ...Pacific and Interior Northwest... Days 2-3... A deepening trough over the Pacific will interact with a building ridge across the Desert Southwest to funnel strengthening S/SW flow into the Pacific Northwest beginning Sunday. This will begin to advect higher moisture onshore as IVT pushes above 250 kg/m/s according to GEFS and ECENS probabilities. Into this moistening column, despite the primary trough cutting off and remaining over the Pacific, a weak shortwave and accompanying vorticity lobe will swing onshore Sunday evening, and work together with the RRQ of a jet streak over Canada to induce lift. This will result in increasing wintry precipitation over the WA Cascades and Olympics, pivoting into the Northern Rockies by the end of the forecast period. Snow levels will generally be around 4000 ft during the heaviest precipitation, but will crash to as low as 1500 ft just before precip ends Monday aftn. This combined with the transient nature of forcing suggests most of the impactful snow will remain above pass levels, but WPC probabilities during D3 rise to as high as 70-90% for 4+ inches in the WA Cascades, Olympics, and near Glacier NP. Weiss