Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 442 PM EDT Sun Mar 26 2023 Valid 00Z Mon Mar 27 2023 - 00Z Thu Mar 30 2023 ...Great Lakes and Northeast... Days 1/2 and 3... Vort lobe that caused a narrow stripe of heavy snow over Neb/IA last night into today will redevelop this evening as it crosses into the L.P. of MI until it is replaced by a following impulse currently over the OK Panhandle crossing the Midwest late tonight and over the Northeast Monday before shifting off the northern Mid-Atlantic coast Monday evening. The availability of some Gulf-sourced moisture with these impulses will allow some moderate precip rates. Dynamic banding north of a weak surface low allows some localized heavy snow tonight over the L.P. of MI with a risk for moderate snow late tonight over the eastern Great Lakes including in the Buffalo metro. The developing coastal low over the Mid-Atlantic Monday allows broader precip development, though the majority of precip is during the max diurnal which here in late March usually greatly limits accumulation potential, though areas at elevation in PA/NY with the Day 1.5 snow probs for 4"+ 20 to 30 percent over western NY as well as the Catskills and the southern Adirondacks with further low probs in the Greens of southern VT into the Berkshires of western Mass. On Tuesday night, a shortwave trough rotating around a deep low centered over western Hudson Bay swings from western Ontario and crosses the northern Great Lakes on Wednesday. Continental air with this wave looks to limit precip, though LES develops in NWly flow raising low probabilities for 4"+ over the U.P. and northwestern L.P. of MI. The upper trough begins to eject east Monday evening with a consensus for snow to weaken as it crosses KS into MO Monday night. ...Northern Rockies, Central High Plains... Days 1-2... An upper low over WY this afternoon opens into a trough tonight, dipping into CO late tonight before slowly shifting onto the central High Plains Monday. Upslope flow around the Bighorns and Red Lodge continues tonight where there are moderately-high probs for 4"+ additional snow. A lee side trough develops over the High Plains of CO tonight with moderate to locally heavy snow developing across northeastern CO where there are moderate probs for 4"+ snowfall which extends over the borders into WY/Neb/KS. ...Oregon/California and Great Basin... Days 2-3... Potent upper low shifting south off the BC coast will remain offshore, but a reinforcing trough Monday causes it to shift toward the OR/CA coast Monday night before tracking south down the CA coast through Wednesday night. Plume of moisture will surge ahead of the low pressure and cold front into NorCal and southern OR Monday night as precipitable water values rise to between +1 to +2 sigma. Low snow levels around 2000ft will rise to 4000-5000ft for the CA coastal ranges in the milder/humid air ahead of the cold front with snow levels around 4000ft expected for the Sierra Nevada. Heavy snow is expected for the higher terrain with snowfall rates 1-2"/hr shifting southeast from the Klamath Monday night through the Sierra Nevada Tuesday/Tuesday night as the moisture plumes sinks southeastward. WPC probabilities for at least 12 inches of snow are high on Day 2 over the Klamath/Shasta Siskiyou and northern/central Sierra Nevada and then high over the southern Sierra on Day 3. The initial wave of heavy precip crosses SoCal Wednesday with snow levels there 5000-6000ft with Day 3 snow probabilities for 6"+ limited to the highest terrain there. The probability of significant icing Days 1-3 is less than 5%. Jackson