Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 511 PM EDT Fri Mar 28 2025 Valid 00Z Sat Mar 29 2025 - 00Z Tue Apr 01 2025 ...Northern/Central Rockies... Days 1/2... A shortwave trough ejecting from the remnant/occluded low off WA crosses the PacNW tonight and the Great Basin through Saturday night. This maintains moisture spreading across the northern Great Basin and Rockies will begin to interact with a developing low-to- mid level baroclinic zone and periods of enhanced forcing associated with the inland moving troughs to produce light-to- moderate precipitation, including mountain snow from the northern to the central Rockies. Precipitation coverage is expected to increase tonight, with unsettled weather continuing into Sunday with a weak area of convergence on Sunday between western MT and northern CO. Snow levels beginning above 5000ft in the northern Rockies are forecast to dip below 4000ft in some location by late Saturday. In the central Rockies, snow levels will drop to 7000-8000ft in the Colorado ranges and around 5000-6000ft across northern Utah. WPC Day 2 probabilities for >8" of snow are generally 40-70% over southwest MT, the Absarokas and Wind River Range, and the Park Range and Medicine Bow Mountains of northern CO. ...South Dakota, Minnesota, and Northern Wisconsin/Michigan... Days 1/2... ...Back to back impactful winter systems through Sunday... Inverted trough from central High Plains up through lower MI persists tonight as an upper low approaching the northern Rockies this afternoon allows lee-side cyclogenesis to focus over western KS through Saturday morning with a more potent low track from KS to MI Saturday through Sunday evening. A very strong baroclinic zone (it's currently low 80s in southwest MN and mid 20s in the Arrowhead) maintains cold over northern MN/WI/the U.P. through this weekend while warm air rides over the boundary to the south. Ongoing wintry mix continues tonight with a slow southward shift. Day 1 ice probs for >0.1" additional after 00Z is about 20% over far northern WI into the western U.P., but 50-80% over far northeast WI and central/eastern U.P. and northern L.P. with 70% probs for >0.25" over the northern L.P. The developing low track over KS on Saturday allows fgen/deformation banding to develop over over southwest SD into northwest Neb. Localized banding should overcome the strong March diurnal insolation, but that should be fairly narrow. Day 1.5 snow probs for >4" are 30-60% mainly over south-central SD and the Black Hills. The impactful wintry weather continues resumes Saturday night over MN/WI/MI as snow bands intensify in the increasing right entrance jet dynamics and the comma head forcing from the low tracking over IA. These snow bands are increasingly likely over north-central MN, far northern WI and western/central U.P. which would put heavy wet snow over areas currently getting ice accretion. Day 2 snow probs for >4" are 30-60% from the Sisseton Hills of northeast SD through the central U.P. and North Shore of MN with 50-70% probs for >6" over far northern WI through the Keweenaw Peninsula. The wintry mix swath is just south of the snow with accumulating sleet and ice expected to expand south as the cold air wins/advances. Day 2 ice probs for >0.25" are 30-70% from central MN through northern WI/southern/eastern U.P. and the northern L.P. with a max around 80% in northeast WI. ...Northeast... Days 1-3... ...Prolonged wintry mix over northern NY/New England through Sunday... The inverted trough causing a wintry mix over the northern Great Lakes today spreads east over northern NY and central New England this evening with the strong baroclinic zone maintaining fgen precip/wintry mix through this weekend for portions of New England. The approaching low crosses New England on Monday. The heavy snowfall threat peaks late tonight from Lake Champlain through northern NH into southern Maine as a jet max passes to the north of New England and 925-850mb WAA is strongest. 12Z HREF depicts 30-40% chances for 1"/hr snowfall rates from 06Z to 13Z Saturday across the northern tip of NY and northern VT/NH. Day 1 WPC snowfall probabilities for >6" are 30-60% mainly over the northern Greens and the Presidential Range of NH. South of this heavy snow threat between the northern Adirondacks and much of central/southern VT and NH, 850-750mb warm nose allows for a transition zone of sleet/freezing rain. After the brief burst of heavier precip early Sat, forcing weakens and there is left a weak stream of moisture overrunning a CAD signature due to a strong 1030mb High situated over the James Bay. This potentially significant icing threat is expected to linger through Sunday until the surface low across the Midwest begins to strengthen and push warmer air northward across New England by Sunday evening. However, the CAD signature in place will continue to support freezing rain across the typically colder valley locations and areas banked along the Green/White mountains. Day 1 WPC probabilities for >0.25" ice (ending 00Z/Sun) are 40-70% for the Thousand Islands area, the northern Adirondacks and south-central VT/NH. This is followed by Day 2 values of 20-50% for an additional 0.25" over the same areas with some expansion through central VT/NH. ...OR Cascades...Klamath...and northern/central Sierra Nevada... Day 3... The next cold core low drifts toward OR, but remains offshore Sunday through Monday. A rich plume of moisture shifts inland Sunday with renewed enhancement from an ejecting shortwave trough Sunday night producing heavy precip over the northern half of CA Monday. Day 3 snow probs for >8" are 40-90% in the southern OR Cascades, the Klamath/Trinity Alps, and northern/central Sierra Nevada with snow levels of 5000-6000ft Sunday dropping to 4000-5000ft by Monday morning. Jackson