Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 356 AM EST Sun Mar 05 2023 Valid 12Z Sun Mar 05 2023 - 12Z Wed Mar 08 2023 ...Sierra Nevada up through southern Oregon Coastal Ranges, the Pacific Northwest and the Intermountain West... Days 1-3... A persistent, nearly stationary upper level low will remain just offshore the Oregon/Washington coast through Tuesday. Multiple lobes of vorticity will pivot underneath the main low center with the strongest today as the westerly Pacific jet over northern California east to the central Rockies reaches 150+ kts. This has led to a favorable overlap of height falls, PVA, and left exit diffluence to provide a large area of synoptic support for widespread precipitation over central and northern CA and terrain over central Utah/northern Colorado into tonight. Snow levels remain below 2000ft through the event. Impactful snow is likely at many of the mountain passes with at least moderate accumulations in the coastal ranges and light snow likely even in the lowlands of California with cold air and generally light onshore flow over the Pacific Northwest leading to localized moderate snowfall. Day 1 snow probabilities are high for 8-12"+ over the Sierra Nevada with localized amounts of two feet likely in the High Sierra through tonight. A reinforcing trough rounding the offshore low will focus energy out there Monday with the only Day 2 probabilities for >6" (and moderate at that) over the Klamath, California Cascades, and Sierra Nevada. Similar results on Tuesday with just a nudge north with moderate >6" probs for the northern Sierra Nevada, Klamath and Cascades from California into southern Oregon. ...Northern Plains through Upper Midwest/Northern Great Lakes... Days 1-2... A shortwave trough currently over Nevada ejects ENE over the north-central Rockies tonight with lee cyclogenesis over the north-central High Plains today that shifts east over the Upper Midwest tonight into Monday. Favorable synoptic support for snow exists thanks to left exit region upper diffluence from the potent Pacific jet spreading in, height falls, and PVA while moist advection ahead of this low will lift up the MS Valley and into the Northern Plains with PWs around 0.5in (+1 sigma). This will lead to an enhanced area of frontogenetical forcing where a stripe of moderate to locally heavy snowfall is expected. 00Z guidance has shifted south a bit with the Day 1 snow probs for >6" moderate over much of southern ND through the SD border. An increasingly tight pressure gradient across North Dakota will result in strong winds and increase impacts. Combined with the falling snow, reduced visibility and blowing snow is likely. Translation to a Midwest surface low occurs this afternoon/evening with a resultant gap in notable snowfall over north-central MN before refocusing over the North Shore of MN (which will have Superior lake enhancement) and over northern WI and the U.P where there are low to moderate probabilities for >6" for Day 1.5. This area then shifts east slowly with Day 2 snow probs for >6" moderate over the U.P. and northern L.P. of MI. The probability of significant icing into the midweek is less than 10 percent. Jackson