Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 342 PM EST Tue Mar 05 2024 Valid 00Z Wed Mar 06 2024 - 00Z Sat Mar 09 2024 ...Western U.S... Days 1-2... An axis of moisture ahead of an upper low off well off the CA coast continues to be reinforced over far northern CA through the WY Rockies, producing moderate to topographically enhanced heavy snow through Wednesday morning with snow levels generally around 5000ft. Day 1 PWPF for >8" are 40-80% for terrain ENE from the Shasta Siskiyou through the western WY ranges. The upper low will move into central/southern CA Wednesday evening with moisture into SoCal with snow levels generally around 6000ft for Transverse/Peninsular ranges. Day 2 PWPF are 10-40% for >6" in the highest portions of those ranges. ...Central/Southern Rockies onto the Plains... Day 3... The reinforcing low rounding the Western U.S. trough reaches southern CA Wednesday night before tracking over southern NM Thursday night and the TX Panhandle on Friday. Lee-side cyclogenesis develops over eastern NM Thursday afternoon which is met by a cold front pushing down the Front Range that reaches northeastern NM/the TX Panhandle by Thursday evening. Along with the help from a 1030mb sfc high centered over the northern Plains, a tight baroclinic zone sets up near the CO/NM border with northeasterly upslope flow into the Sangre de Christos and adjacent high Plains Thursday night. Gulf-sourced moisture rounding the low and developing inverted trough over the southern/central Plains allows a focus of moderate to locally heavy snow to focus on the Raton Mesa/Sangre de Christos into Friday while upslope snow over southern WY/the CO Front Range should be more progressive. The Day 3 PWPF for >8" snow is 40-70% for the eastern slopes of the CO Front Range/Pikes Peak/Sangre de Christos with 40-60% probabilities over the I-25 corridor on the north slope of the Raton Mesa. Bands of snow are expected farther east over the central High Plains in NE/KS inverted trough shifts east Thursday night/Friday. As of now the best chances out on the plains are Day 2.5 in southwest Neb where probabilities for >6" are 20-30%. ...Northern Plains... Days 1/2... A compact mid-level low over southern Alberta this evening will shift ESE to the northern Dakota border through Wednesday before lifting a bit into Manitoba Wednesday night. Meanwhile, a lee-side low over the eastern MT/WY border shifts to the Neb/SB border tonight before lifting to northern MN by Wednesday evening. Southerly flow ahead of the sfc low brings moderate bands of snow to northern ND and far northwestern MN Wednesday afternoon/evening. Sufficient cold conditions ahead of the wave look to keep it all snow along the Canadian border where Day 1.5 PWPF for >6" is 20-30%. ...Northern New England... Day 2... A northern stream shortwave trough over Quebec will push a over northern New England early Wednesday with a southern stream coastal low developing over the northern Mid-Atlantic coast Wednesday evening. A 1035mb sfc high pressure over James Bay/northern Quebec push colder/drier air down the St. Lawrence Valley and northern Maine, allowing snow bands to develop over northern Maine late Wednesday night into Thursday on the north side of the precipitation shield. Guidance is still dispersive with the intensity of these snow bands with Day 2 PWPF currently around 10% for >6" in northern Maine, though individual 12Z deterministic runs indicate the potential for heavy snow including the GFS and NAM. Will need to continue monitoring for heavy snow potential in northern Maine. The probability of 0.25" icing is less than 10 percent Days 1-3. Jackson