Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 230 AM EDT Sat Apr 6 2024 Valid 12Z Sat Apr 06 2024 - 12Z Tue Apr 09 2024 ...Northeast... Day 1... The long-lived nor'easter will finally start to exit the region today, with mainly light wrap-around snow for the Northeast (light rain on the southern side) and any additional appreciable snow limited to the highest peaks (e.g., the Presidential Range and the higher peaks of the Appalachians in Maine) where WPC probabilities for another 4" or more are >50%. ...Western U.S.... Days 1-3... Deep upper trough moving through the West has started to shift to its next phase -- closing off a mid-level center near the Four Corners and lifting that northeastward into the central Plains this evening. The northern extent of the trough over the interior PacNW/northern Great Basin/western Montana will slowly fill as the Plains system reaches maximum intensity Sunday morning. At the surface, low pressure will organize over northeastern CO this morning and lift northeastward while continuing to deepen, thanks to a strongly buckled upper jet over the southern Plains, resulting in broad lift over Nebraska and into western SD/eastern WY. This will carry a deep (mid 980s mb) low into western NE overnight tonight before scooting eastward Sunday afternoon. Strong dynamics with the system will promote areas of heavy precipitation east of the Continental Divide to the Plains, but antecedent cold air is lacking over much of the region outside the mountains and foothills. Nevertheless, these types of systems can induce a snowier profile as colder air gets wrapped into the system and dynamical cooling due to strong lift in the column can change rain to snow in heavier bursts. The areas of eastern WY, especially into the Bighorns and Laramie mountains, and into the Black Hills have the highest probabilities of at least a foot of snow through this event (WPC probabilities >70%), with lower to moderate probabilities in between. As the low intensifies, a modest tap of Gulf moisture will advect northward then northwestward into and around the low, with strong IVT (>99th percentile) over South Dakota nosing into the Black Hills this evening. This will support snow rates of 1-2"/hr into Sunday, along with gusty winds up to 50mph, producing blizzard-like conditions. Favorable FGEN coincident with a deformation axis oriented NW to SE over eastern WY will likely yield >2ft snowfall for some areas, especially in the higher terrain. This is supported in the WPC PWPF with probs for >24" >50% in the Bighorns. By D3, the system over the Plains will be gone, but another trough will bring some snow to the Cascades in WA while another sneaky shortwave on the far backside of the exiting Plains system strengthens into another close low into AZ and NM. This will spread some snowfall into the central/southern Rockies late in the period, with low-moderate (<50%) probabilities of at least 4 inches of snow into the Sangre de Cristos in CO/NM. Fracasso The probability of significant icing of at least 0.25 inches is less than 10 percent.