Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 352 PM EDT Mon Mar 25 2024 Valid 00Z Tue Mar 26 2024 - 00Z Fri Mar 29 2024 ...Southern Rockies... Day 1... Southwest side of the broad troughing over the western/central US will carry some embedded vorticity through the Southwest/Southern Rockies this evening and into Tuesday. A few inches of additional snowfall are likely over much of the mountainous areas, especially the White and Mogollon Mountains in AZ and NM, respectively where over ten inches are possible. ...Northern Plains & Upper Midwest... Day 1... Major winter storm will progress through the Corn Belt into the Upper Midwest tonight/early Tuesday, with the trailing mid-level vort center becomming the dominant entity that will help carry it into western Ontario late Tue into early Wed (though again trailed by another vort center). Deformation snow on the NW side of the low will continue to translate northeastward this evening over MN with mid-level-forced snow over NE/KS moving eastward in tandem with CAA behind the front. Winds will remain quite gusty this evening with blizzard conditions due to blowing snow possible. Additional snow will be light- modest, with the highest totals after 00Z over northern/northeastern MN where WPC probabilities for at least 4 more inches are high (>70%). Southeast of this axis, warm air aloft atop sub-freezing surface temperatures will promote a SW to NE axis of freezing rain/sleet from southern MN northeastward across the Arrowhead. Additional icing will be around several hundredths to just over a tenth of an inch or so. The entire system will slowly ramp down with plenty of wrap-around light snow over northern MN into Tuesday, but with only an inch or two likely except for perhaps right along the Canadian border. ...PacNW/Northern Great Basin... Days 1-3... Northwest flow downstream of an upper ridge axis south of the Gulf of Alaska will continue to funnel mid-level impulses into the Pacific Northwest and northern Great Basin through Tuesday, with snow confined to the Cascades and northern/central Rockies as the upper jet slowly weakens and moves eastward. By Wednesday, a much more coherent upper low will form/deepen just south of 50N near 140W with a plume of moisture tied back to the subtropics approaching the WA/OR coast. This will move ashore starting early Wednesday with snow levels rising to around 5000ft ahead of the cold front in the Cascades mid-day Wednesday then fall back to around 4000ft post-FROPA as precipitation starts to wane and eventually as low as about 3000ft by Thursday morning. In the Cascades, WPC probabilities for at least eight inches over the next few days are >50% above about 4000ft. Precipitation will continue into the northern Rockies/Great Basin beneath the LFQ of the advancing upper jet, favored over the Blue Mountains into the central ID ranges and western WY where WPC probabilities for at least six inches are high (>70%). Farther south into California, moisture plume will be a bit more potent, with IVT values > 400 kg/m/s (~98th percentile) into the NorCal ranges (Shasta/Siskiyous/Trinity) by late Wednesday (with the cold front) through Thursday (associated with the trailing upper jet streak). Snow levels >6000ft ahead of the front will fall to <5000ft behind it, then even to 4500ft or so by Thursday with continued onshore flow. Snowfall days 2-3 will be modest over the northern to central Sierra, with WPC probabilities for at least 12 inches >50% above about 6000ft or so. Fracasso ***Key Messages for Plains-Upper Midwest Winter Storm*** --Major winter storm continues into Tuesday Snow and strong winds will continue from the Central Plains to northern Minnesota through tonight, along with sleet and freezing rain in parts of the Upper Mississippi Valley. --Hazardous impacts due to snow and wind Plan on slippery road conditions. Blowing and falling snow will significantly reduce visibility, and blizzard conditions will persist into Tuesday across portions of the Plains and northern Minnesota. Travel may be very difficult or impossible at times. Power outages and tree damage are possible in some areas due to heavy snow, icing, and strong winds. --Gradual Improvements Snow and winds will gradually diminish from southwest to northeast across the region on Tuesday. However, areas of blowing snow may persist.