Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 435 PM EDT Wed Mar 27 2024 Valid 00Z Thu Mar 28 2024 - 00Z Sun Mar 31 2024 ...Upper Peninsula of Michigan... Day 1... A reinforcing trough rounding the upper low over Ontario will continue to provide cold westerly flow over Lake Superior tonight, producing locally heavy LES over the U.P. of Michigan. Day 1 WPC PWPF for >6" additional snow is 40-60% over southern portions of the Keweenaw Peninsula. Weakening flow and NVA causes the LES bands to diminish through Thursday. ...The West... Days 1-3... Closed low stalled west of Vancouver Island this afternoon will continue to direct moisture across the West Coast through the Northern and Central Rockies through Thursday. A reinforcing trough around this low pushes over far northern CA tonight, allowing the heavier precip focus on the Sierra Nevada where Day 1 PWPF for >8" are categorical with snow levels dropping from 6000ft to around 3500ft overnight. Moderate snow rates are expected over the Shasta- Siskiyou, up the Cascades and Olympics, then east over Blue, Sawtooth, Salmon River, and western WY ranges where Day 1 PWPF for >8" are generally 40-80% with snow levels falling as low as 3,000ft in the WA Cascades and Olympics. The next reinforcing trough rounding the upper low off the PacNW Thursday night/Friday has a partial phase which shifts the low pressure focus to off the far northern CA coast by late Friday. This disrupts the onshore moisture flux with a lull in heavy snow over Day 2 (00Z Fri-00Z Sat) with moderate snow focused over the remnant frontal zone over the eastern Great Basin to the northern CO Rockies where Day 2 PWPF for >8" is 30-50% over terrain from eastern NV over north-central UT to the northern CO Rockies. The reinvigorated low off CA focuses Pacific moisture influx across CA with renewed heavy snow for the length of the Sierra Nevada and higher elevations of the Transverse and Peninsular ranges with snow levels generally 5000ft. The cold front ahead of this low is still progged to be fairly progressive, so the heavy snow focus in the moisture swath of this frontal zone would shift south over CA Friday night through Saturday. Day 3 PWPF for >8" is 40-80% down the length of the Sierra Nevada and similar for the SoCal ranges. ...New England... Days 2/3... Southern stream wave currently over the western Gulf coast takes on a negative tilt off the Carolinas Thursday night before shifting north off the New England Coast Friday. This developed low poses the risk for decent banding on the western side of the comma head precip shield which would be over northern NH/Maine Friday/Friday night before the system lifts away Saturday. Guidance still has uncertainty with more snow farther west in the 12Z GFS/UKMET while the 12Z CMC/ECMWF went farther east. Will need to continue to monitor this back side heavy snow band threat. Jackson