Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 349 AM EST Fri Feb 16 2024 Valid 12Z Fri Feb 16 2024 - 12Z Mon Feb 19 2024 ...North-Central Rockies... Day 1... An upper level trough on the downwind side of an omega high centered over the Yukon will slowly eject southeast from eastern Washington to the Colorado Rockies through tonight. The heaviest snow continues ahead of this trough axis over western Wyoming to northern Utah and over southern Wyoming through northern Colorado ranges where Day 1 PWPF are over 50% for an additional >6" with snow levels generally 4000-5000ft. ...Great Lakes... Days 1-3... Lake Effect Snow (LES) on WNWly flow into the U.P. continues today in conjunction with height falls out of Ontario. This flow and associated LES expands over the eastern Great Lakes tonight in the wake of low pressure shifting east over the Mid-Atlantic and continues until turning Wly Saturday night. Single band LES into the Tug Hill is likely on Lake Ontario Sunday where Day 3 probs are 40-60% for >4". ...Mid-MS Valley through Central Appalachians/Mid-Atlantic... Day 1... A positively-tilted mid-level trough shifting from MN through the Great Lakes tonight combines with a shortwave trough from the central Plains to promote development of a surface low currently over the southern Plains as it moves over Tennessee today and the southern Mid-Atlantic tonight. To the north of this low, a transition from rain to snow will occur deeper into the colder air, with banded snow aided by an advancing arc of FGEN that will promote increasingly moderate snow bands this morning over northern Missouri and central Illinois/Indiana and then this evening over the central Appalachians, then overnight along the Mason-Dixon line to central NJ. SLRs will trend from near/below 10:1 near the low to over 15:1 well into the cold side where more energetic lift into a favorable DGZ occurs. Day 1 PWPF for >4" snow are 40-70% north of St Louis from northeastern Missouri through central Illinois along I-72. Values decrease to 20-30% across central Indiana along I-74/70 before diminishing over southern Ohio. However, PWPF rapidly increases east from the Ohio River over West Virginia, western Maryland and into the Laurel Highlands where values for >6" are 40-70%. An axis of heavier snow is likely in this zone with the ridges east of the Allegheny Front to the Blue Ridge in Virginia most likely to see 6" tonight. This fast moving system, riding a 175kt+ Wly jet redevelops over along the North Carolina/Virginia border overnight before it quickly shifts east of the southern DelMarVa Peninsula. PWPF for >4" are 40-60% extend east mainly on the north side of the Mason-Dixon line through the Philly metro and into central NJ where the most favorable FGEN and dendritic growth persists. Just south, 20-40% probs do extend over northern Virginia/central Maryland and northern Delaware where more progressive, but still locally heavy bands are expected north of the low center. ...West Coast... Days 2/3... The Omega high breaks down/drifts inland over western Canada tonight through Saturday as the next Pacific trough approaches the Pacific Northwest and directs an Atmospheric River into California. Strong southerly flow will raise snow levels to around 6000ft as precip moves inland Saturday afternoon/night before diminishing into the ridge with a weakening mid-level shortwave carrying light snow into the northern Great Basin into Idaho, western Wyoming and northern Utah. The next low then approaches the Oregon/California border on Sunday. Day 2 PWPF for >6" remain 40-80% for the Sierra Nevada, Shasta/Siskiyou, and higher OR Cascades with Day 3 similar for the California ranges as well as 30-40% probs for selected ranges of ID into WY. Resident cold air over the Columbia Basin/Gorge does allow for some risk for light freezing rain in the surrounding Cascades and perhaps the northern Oregon Coast Ranges Saturday/Saturday night where Day 2 PWPF for >0.1" are 10-20%. Jackson