Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 412 PM EDT Tue Apr 23 2024 Valid 00Z Wed Apr 24 2024 - 00Z Sat Apr 27 2024 ...Northern Maine... Days 1/2... A potent lobe of a mid-level low east of Hudson Bay is crossing James Bay this afternoon and will take on a negative tilt as it reaches northern Maine Wednesday afternoon. Strong ridging and cold air quickly follows this wave which will bring a quick end to precipitation. The question is how much precipitation can fall Wednesday afternoon over northern Maine after the column is cold enough for snow. As of now the most likely forecast is 1-3" over far northern Maine, though a few ensemble members and the 12Z GFS have heavier snow which leads to Day 1.5 PWPF for >4" of 40% over the northern border of Maine. ...White Mountains Along California/Nevada Border... Days 1/2.... A mid-level southern stream low in a positively-tilted trough is currently well west of SoCal, but as it approaches/opens into a wave on Wednesday flow will promote low level cyclogenesis over the Great Basin which will direct Pacific moisture back to the White Mountains and the south-central Sierra Nevada. A narrow swath of precip over central NV back southwest through this terrain is expected to develop Wednesday afternoon, then continue until the trough axis passage late Wednesday night. Little movement to this swath could lead to moderate to locally heavy snowfall above the snow level which will be around 9000ft. High terrain of the White Mtns snowfall of 8-12" is possible with Day 1.5 PWPF for >8" around 40% (though smoothing is likely limiting values of this narrow mountain range). ...The West... Day 3... The aforementioned southern stream wave crossing the Southwest Wednesday night will shift ENE over the southern Rockies late Thursday with generally moderate snowfall over high terrain with snow levels around 9000ft. The next wave is currently a series of impulses over the northern Pacific that will track south of a low currently over the Alaskan Panhandle and develop into a trough into the Pacific Northwest late Thursday that digs southeast/amplifies into a more significant trough over the Great Basin by late Friday. As the trough develops, broad Pacific flow into the West Coast brings moisture quickly east to the Rockies Thursday night/Friday. Height falls under the trough allows snow levels to drop to around 5000ft over the Northwest, to around 6000ft over the Intermountain West/northern Rockies, and 7000-8000ft over the central/southern Rockies. The Day 3 PWPF for >6" is 30-60% over the OR/southern WA Cascades, higher terrain over the Great Basin ranges, especially over northeast NV and UT, and the greater Absarokas in ID/MT/WY. This wave further develops Friday night with continued snow expected over the central/southern Rockies well into the weekend. The probability of significant icing is less than 10 percent. Jackson