Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 422 PM EDT Sun Mar 24 2024 Valid 00Z Mon Mar 25 2024 - 00Z Thu Mar 28 2024 ...The West/Great Basin/Northern Rockies/Four Corners... Days 1-3... Deep and broad upper trough moving through the Great Basin/Four Corners this evening will continue to advance into the Plains, being the driver for the northern Plains/Upper Midwest system. Light snow will continue over the Mogollon Rim, Wasatch, and CO Rockies D1 with higher accumulations at high elevations. Farther north, northern stream vorticity will swing through Montana, helping to spur additional snowfall over the Bitteroots. Into D2, upper jet will arc out of the northeast Pacific into NorCal and SW OR, favoring continued unsettled weather into the Pac NW and northern Great Basin, where light snow will continue in the mountains. Upper ridging will briefly push into the region late Tue/early Wed before another trough starts to enter the Pac NW by the end of the period. Moisture plume will focus into coastal WA/OR with snow for the Cascades and snow levels around 4000ft. ...High Plains/Central Rockies/Upper Midwest... Days 1-2... **Major Winter Storm to Impact Northern High Plains to the Upper Midwest into Early This Week** Low pressure over SE CO will start to trek northeastward tonight as the mid-level shortwave exits NM amid a sharpening upper flow. With the jet lifting into the Upper Midwest/Corn Belt, strong divergence beneath the LFQ of the increasinly S-shaped jet will promote widespread modest QPF over the northern tier tonight through Monday. 50-60kt southerly flow at 850mb will bring in substantial moisture to the region that will wrap around the surface cyclone moving into Iowa by Monday evening. Trailing mid-level vorticity will swing around the backside of the lead center as temperatures fall behind the storm below freezing. Over the eastern side of the CO Rockies to the Front Range and western central High Plains, this surge of colder air via a strong cold front will change rain to snow outside the mountains with northerly/north-northeasterly flow favoring the Palmer Divide into the Sangre de Cristos and higher totals into the Rockies themselves. WPC probabilities for at least 6 inches of snow are highest (>70%) above 5500-6000ft. Onto the Plains northeastward, the vigorous system will favor heavy snow to the northwest of its low track and increasing wind around the entire system, leading to blowing and drifting snow. Strong WAA northward will promoted heavier snow rates (1-2"/hr per the WPC snowband tool) amid robust FGEN deeper into the cold air, but overrunning milder air will also allow for a changeover from rain to snow with a period of icing and some sleet in between. The heavy snow axis will lie from western/central NE northewastward to northeastern SD and across central to northeastern MN where snow is the dominant or only p-type. Just to the southeast of that line will be an area of freezing rain which may accrete to a couple tenths of an inch, especially along the SD/MN border where the pivot point of the system will linger for a time as the lead 500mb vort is subsumed by the trailing one. By Monday evening/Tuesday morning, the low will continue to head northeastward into northwestern WI, enhancing low- level convergence along the west side of Lake Superior but also allowing for milder air aloft to change some areas over to freezing rain. The system will finally exit into Canada late Tuesday but with a fair amount of wrap-around snow showers over the Upper Midwest. Storm total probabilities of at least 8 inches of snow are at least 50% from roughly far northwestern KS northeastward to eastern SD and across much of central to northern and northeastern MN as well as far northwestern WI. Within this area, probabilities of at least 12 inches are highest over northeastern MN and through the Arrowhead along the Lake Superior shore. Fracasso ***Key Messages for Plains-Upper Midwest Winter Storm*** --A high-impact winter storm unfolding A vigorous storm will impact the Northern/Central Plains into the Upper Midwest through Tuesday. Heavy snow and increasingly gusty winds will expand through much of the region overnight along with some sleet and freezing rain. --Widespread heavy snow expected Heavy snow is forecast from western Nebraska northeastward to central and northern Minnesota. Snow may accumulate at 1-2"/hr in heavier bands tonight across Minnesota and Wisconsin as well as central Nebraska. Storm total snowfall may exceed a foot (>50% chance) over northern and northeastern Minnesota. --Hazardous impacts due to snow, snow load, and wind Heavy snow and gusty winds over 50 mph will produce blizzard conditions with near zero visibility into early Tuesday. Travel could be nearly impossible. Power outages and tree damage are likely in some areas due to the heavy and wet snow combined with icing and strong winds. --Strong wind gusts in the Central and Southern Plains Wind gusts over 50 mph today may result in power outages, blowing dust with reduced visibility, difficult travel, and property damage. Critical fire weather conditions are in effect this evening and tomorrow over the Southern High Plains into South Texas.