Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 424 AM EST Fri Jan 12 2024 Valid 12Z Fri Jan 12 2024 - 12Z Mon Jan 15 2024 ...Central Plains to the Great Lakes and Interior Northeast... Days 1-3... A soon-to-be negatively-tilted trough axis over North Texas early this morning will continue to rapidly develop as it turns northeast over MO today, reaching southern Lake Michigan by this evening. Complimentary jet become S-shaped across the Great Lakes will drive strong upper level divergence and robust surface cyclogenesis with a deepening area of low pressure lifting from the Ozarks early this morning to the L.P. of MI tonight. A swath of heavy snow from eastern Neb through IA into northern IL will continue to slowly pivot northeast downstream of the low, lifting over WI and MI through tonight. As the low tracks northeast to Quebec on Saturday, intense lake-effect snow will develop, covering all five Great Lakes by Saturday night which continues into midweek. A wintry mix in the rain to snow transition zone through the WAA precip continues this morning in a stripe over northern IL before the system becomes dominated by just a rain-snow delineation. North in the snow zone, significant snowfall is expected on the northwest side of the low as a deformation band forms and slowly pivots across the area, coincident with an intense TROWAL as the WCB wraps into the low with a deep DGZ. The areas of greatest snow potential (15-20 inches) remain eastern WI where the pivoting band has lake enhancement which is also present over northeast portions of the L.P. and in the Huron Mtns of the U.P. where lake enhancement turns into lake effect snow. The powerful cyclone reaches peak intensity over the L.P. tonight with MSLP in the low to mid 970s making for very strong winds and likely blizzard conditions north and then west of the low. Day 1 WPC probabilities for at least 12 inches after 12Z are greater than 50% over southern and eastern WI, northeastern portions of the L.P. and the Huron Mtns in the U.P. which is the favored snow belt favored in N-NW flow. There, strong northwest to eventually west flow on the back side of the low envelopes all of the Great Lakes with LES beginning off Lake Superior Saturday and the rest of the Great Lakes by late Saturday night and continuing in earnest through at least Sunday night with LES persisting over all the lakes into Wednesday. Day 2 snow probs for more than 8 inches are over 50% for typical NW and W snow belts in the U.P. including the Porcupine Mtns and 20-40% along the western shore of MI, around Buffalo, and the Tug Hill. The powerful wind should fracture dendrites which should limit max SLRs despite the deep, saturated DGZ. Day 3 snow probs for more than 6 inches are high around Buffalo and on the Tug Hill with some additional values in the eastern U.P. Westerly flow LES then continues trough Tuesday/possibly Wednesday. On the eastern side of the approaching front, cold air mass in place over the interior Northeast will slowly be eroded as broad southerly flow scours out sub-freezing temperatures. The uneven erosion in the column will likely lead to a period of snow to freezing rain to rain in most areas of eastern NY and interior New England outside northern Maine as a triple point low moves across the area. Before the changeover, several inches of snow will likely accumulate over terrain in interior portions of the Northeast with Day 1.5 WPC snow probabilities for more than 6 inches highest (generally >70%) over the Adirondacks, Green & White Mtns, and interior Maine (North Woods). ...The West... Days 1-3... An active wintry pattern will continue throughout much of the mountain ranges along the West Coast, much of the Great Basin to the Colorado Rockies through this weekend across the boundary of Arctic cold air over this region. A shortwave trough pushing into WA from BC is rounding a deep low centered over Alberta and send a surge of potently cold air over the Northwest today before stalling over southern OR where it will persist through this weekend. A rich plume of 850-700mb moisture running along this boundary, along with topographic lift will allow heavy snow to continue over the OR Cascades, across southern ID, northern UT and the Wasatch, to the CO Rockies today. Day 1 PWPF for >8" are high (over 90%) along the OR Cascades and the Wasatch and moderate (40-70%) over southern ID into northern NV. Strong winds are expected in this tight baroclinic zone with blizzard warnings up in southern ID. Meanwhile a compact southern stream low cuts through the North Pacific/Alaska ridge tonight, reaching the OR Coast late Saturday. This storm system will tap into a conveyor belt of moisture that has origins into the subtropics. The combination of anomalous moisture and a strong 850mb jet will lead to IVT values approaching the 99th climatological percentile being directed at southern Oregon and northern California. This brings further heavy snowfall in the Oregon Cascades with the footprint expanding south through the Sierra Nevada. Confidence is highest in heavy snowfall accumulations along the stationary front from southern Oregon and northern Nevada to the Wasatch which is at the nose of the strong IVT plume emanating out from the northeast Pacific. Day 2 WPC PWPF sports high chances (>80%) for more than 8 inches of snowfall over the OR Cascades/Trinity Alps/Sierra Nevada east through the northern Great Basin ranges, the Wasatch and the CO Rockies. As this wave comes ashore, warm air riding over the Arctic air at the surface sets up a significant freezing rain case for northwest OR into southwest WA. Day 2 PWPF for more than 0.25 inches of ice area 30 to 60% over much of the Willamette Valley south of Portland west through the Coastal Ranges. Ridging begins to shift east into The West Sunday, with precip shifting east. Day 3 PWPF for more than 8 inches is moderately high (50-80%) over the Wasatch and CO Rockies south through the NBM border in the San Juans. All told, three day totals of over 4 feet are expected on the highest OR Cascades and Wasatch with 2 feet or so for the Sierra Nevada and CO Rockies. Also noteworthy are low probabilities for more than two inches over the Portland metro on both Days 1 and 2. ...Mid-South... Day 3... The southern stream shortwave trough that slices through the North Pacific/Alaska ridge tonight crosses the southern Rockies Sunday and rounds the base of the expansive trough over the central part of North America Sunday night. Gulf moisture is available to ridge up and over the cold front that pushes through Texas and well into the Gulf, allowing precip to break out over North Texas/OK before crossing AR into TN and northern MS/AL. Sufficient cold air in this Arctic airmass allows moisture in the DGZ with SLRs in the mid to upper teens. There remains uncertainty with the strength/timing of this wave/reinforcing waves with the 00Z ECMWF stepping back its QPF footprint over the area, but for now the Day 3 snow probs for >4" are 10 to 40% from OK across northern AR well into western TN. Given the strength of the jet under this trough and the particularly cold air, having accumulating snow over this area is a good bet, so stay tuned for further updates. Jackson ***Key Messages for Jan 10-14 Major Winter Storm over the Midwest*** --Conditions Deteriorate Rapidly Today in Midwest Heavy snow will continue to spread across the Upper Midwest today. Snowfall rates of 1 to locally 2 inches per hour will lead to hazardous travel conditions over much of the region --Blizzard Conditions Likely with Strong Winds Winds will increase through tonight in the Midwest and Great Lakes as the storm system rapidly strengthens. Blizzard conditions are likely, particularly in exposed areas. Travel will become dangerous to impossible with whiteout conditions. Power outages are possible. --Lake Effect Snow Persists This Weekend While the larger snow area will diminish on Saturday, the arrival of colder air will generate heavy, wind-driven snow downwind of the Great Lakes this weekend into midweek. Whiteout conditions in the blowing lake effect snow are expected in the stronger lake effect snow bands. --Flooding and Severe Storms in the South and East Severe storms will be possible in the South today and damaging gusts may occur outside of thunderstorms. Heavy rain in the Mid-Atlantic and Northeast tonight and Saturday will lead to renewed rises on rivers and streams and possible flooding. Moderate coastal flooding is likely in the Mid-Atlantic and Northeast Saturday, with significant impacts. Major coastal flooding is possible in New Hampshire and Maine. ***Key Messages for mid-January Arctic Blast*** --Bitter Cold Surges South and Affects Most of U.S. The first significant Arctic outbreak of the winter arrives into the Northwest, the northern Rockies, and northern Plains today, before advancing farther south and east this weekend and early next week. Numerous daily cold records are likely. --Dangerously Cold Wind Chills Expected Sub-zero wind chills will affect much of the U.S. and reach into portions of the South. Wind chills this weekend across the northern Plains and northern Rockies will be below negative 30 degrees on a widespread basis, and as cold as negative 50 to 60 degrees on Saturday morning in Montana and the western Dakotas. This will pose an increased risk of frostbite on exposed skin and hypothermia. Have a cold survival kit if you must travel. --Heavy Snow in the West Today and Saturday Arctic air will gradually lower snow levels in time for the arrival of another storm system in the West today. This will lead to snow and considerable impacts in valleys in Oregon, Idaho, Nevada, and Utah, including the Portland, Boise, and Salt Lake City metro areas. Significant freezing rain is likely Saturday in northwestern Oregon. --Additional Wintry Precipitation Early Next Week Areas of snow, sleet, and freezing rain are likely on the periphery of the advancing Arctic air mass from the interior South into the Northeast. Stay tuned for further details as the forecast may change.