Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 359 PM EST Sat Feb 10 2024 Valid 00Z Sun Feb 11 2024 - 00Z Wed Feb 14 2024 ...Southern Rockies to Texas Panhandle into Oklahoma... Day 1... Positively-tilted upper trough with base along the Arizona/Mexico border with a lee-side low over southwest TX and high pressure over WY will allow precip to blossom over the southern Rockies/southern High Plains through this evening and expand over the TX Panhandle overnight. The upper trough closes back into a low over the TX Panhandle Sunday, increasing PVA and causing the 700-850mb moisture flux to pivot over the southern portions of the Panhandle where snow bands should have hourly snowfall exceeding 1". This area shifts east with the system through the day, reaching the central OK/TX border by late afternoon. Day 1 snow probs for >6" are above 60% in the Sangre de Christos and Sacramento Mtns of NM as well as east-adjacent High Plains and across the southern TX Panhandle. ...Oklahoma/Ozarks to Ohio Valley... Day 2... The upper low further strengthens as it tracks along the Red River into Arkansas Sunday night. This allows dynamic cooling aloft within the deformation axis to sustain moderate-to-heavy snow bands in an otherwise marginal thermal environment from central OK through southern MO through the night. Additional topographic effects from the Ozarks should further enhance the risk of heavy snow there into Monday. The methods used in the WPC PWPF are insufficient for capturing these dynamically cooled bands in marginal thermals, so snow coverage and intensity is often suppressed. Farther east over southern IL/IN, there is a continued risk for localized heavy snow bands, but diurnal effects and lower elevations should mitigate the risk somewhat Monday afternoon. There is a sizable risk for 4-8 inches of snow from central OK through southern MO per deterministic guidance like the 12Z GFS/NAM/ECMWF and for some reason the 12Z CMC suite continues to be very suppressed with snow totals in this storm. ...Upper Ohio Valley through the Northeast... Day 3... The upper low reaches the west side of the central Appalachians by Monday evening, directing high moisture air northward through the Mid-Atlantic and along the Northeast coast. The southern stream Wly jet over the Southeast turns SWly over the Mid-Atlantic, placing the south side coastal low development area over the Chesapeake in its diffluent left exit region off the Mid-Atlantic coast Monday night. The north side of the coastal low is in the diffluent right entrance region of a strong SWly jet over New England, a "kissing jets" setup that will foster rapid coastal low development as it shifts ENE through Tuesday. This setup features no shortage of atmospheric moisture (ECMWF ENS continues to show >90th climatological percentile 500-700mb specific humidity values from the Laurel Highlands on east to the Northeast coast 06Z Tuesday) and the aforementioned synoptic-scale setup is classic for strong upper level divergence, though an overall lack of cold air. This requires snow bands to overcome marginal boundary layer temps via dynamic cooling within the atmospheric column which the 12Z deterministic GFS and ECMWF continue to depict in spades thanks to robust 850-700mb frontogenesis setting up from the upper Ohio Valley through PA Monday night and through southern New England Tuesday morning. These areas beneath this axis of strong frontogenesis should see snowfall rates between 1-2"/hr. Farther south, the lack of cold air will be difficult to over come in locations such as the DC/Baltimore/Philly metro areas Monday night into Tuesday. Increased confidence in the coastal low tracking off the central Mid-Atlantic coast Monday night hones in on the snow swath area a bit with this cycle. Day 3 PWPF for >6" is over 50% from the Laurel Highlands and Alleghenies of western Pennsylvania across the northern half of Pennsylvania, far northern NJ, southern NY (just north of NYC where thermals quickly improve from the coast) and across southern New England except for the southern Cape Cod and Islands. North/south shifts in the track can continue to be expected and given a likely tight northern cutoff to the precip shield, this could have notable effects on snow call in the NY Capital Region for instance. Finally, this low will get down to near 980mb south of Cape Cod Tuesday morning, damaging winds and coastal flooding can be expected. ...Northwest... Days 1-3... A 500mb shortwave trough reaches the western WA Coast late tonight which will direct an influx of 850-500mb moisture into the Pacific Northwest that leads to mountain snow in the Cascades on Sunday. Snow levels in the Cascades will be as low as 3,000ft, but the heaviest totals will generally be confined to elevations above 5,000ft. Snow will continue along the Cascades into Monday as a trailing 500mb disturbance sustains orthogonally-oriented westerly 850-300mb winds into the region, keeping a prolonged period of upslope flow into the mountain range. Day 1.5 WPC PWPF shows high probabilities >70%) for snowfall >6" at elevations above 5,000ft in the Washington Cascades. Farther inland, the initial shortwave trough will advance inland into the Northern Rockies and delivering the same surge in 850-500mb moisture flux into northern Idaho and western Montana starting Sunday and lingering into Monday where Day 2 WPC PWPF are moderate-to-high (40-70%) for snowfall totals >6". Moderate snow then continues Tuesday with Day 3 PWPF for >6" additional above 50% for the Lewis Range and other ranges near Glacier NP. Jackson Key Messages For a Southern Rockies to Northeast Winter Storm... ..Heavy Snow Southern Rockies/Plains Travel impacts expand over the southern Rockies/ High Plains tonight and over the Texas Panhandle into Oklahoma Sunday as the storm drifts east. ..Narrow Heavy Snow Oklahoma to Ohio Valley The storm shifts east-northeast Sunday night through Monday, producing narrow, but heavy bands of snow that impact travel along a path from central Oklahoma into Ohio. ..Northeast Coverage and Impacts Further strengthening into a NorÂEaster along the northern Mid-Atlantic coast Monday night widens the snow bands and coverage of heavy, wet snow over much of the Northeast and southern New England Monday night through Tuesday. This fast-moving storm currently has the highest potential for over 8Â across much of Pennsylvania through southern New England with notable variability persisting in track and strength of the low. Powerful winds and heavy/wet snow should cause damage to trees and powerlines as well as overland travel. Coastal Flooding can also be expected.