Subj : HVYSNOW: Major US Storm To : All From : Dumas Walker Date : Thu Jan 11 2024 08:54 am FOUS11 KWBC 110857 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 356 AM EST Thu Jan 11 2024 Valid 12Z Thu Jan 11 2024 - 12Z Sun Jan 14 2024 ....Great Lakes and Northeast... Day 1... Well-defined shortwave trough over southern WI will quickly shift east across MI and the Northeast today given the strengthening jet to its south while another impulse over northeast ND will drift east across northern MN today. Both will produce Great Lake enhanced snow today with 40-60% Day 1 snow probs for >6" over the North Shore of MN and 40-60% probs for >4" east of Lakes Erie and Ontario for westerly flow lake enhanced snow this afternoon/evening in NY. ....Central Plains, Great Lakes and interior Northeast... Days 1-3... A digging trough crossing AZ today will take on a negative tilt after crossing the southern Rockies this evening as a double-barreled jet becomes more buckled and S-shaped across the Great Lakes into Friday. This will drive strong upper level divergence and rapid surface cyclogenesis with a deepening area of low pressure lifting Friday from the Ozarks through the Midwest and over the L.P. of MI Friday night. This is a strikingly similar track to the exiting system though it forms farther east over the Plains). Snow will rapidly increase in coverage and intensity north of the low this evening over the central Plains and then IA through MI late tonight through Friday evening. As the low tracks away on Saturday, intense lake-effect snow develops, covering all five Great Lakes by Saturday night. Initial WAA over colder sfc air tonight will likely support a wintry mix in the rain to snow transition zone from northeast KS into northern IL. 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. High-end potential is >18" per PWPF from peak development and lake enhancement in southeast WI and northeast portions of the L.P., driven by strong UVV into a sufficiently deep DGZ. Day 1.5 snow probs for >8" are 20-50% from eastern Neb through central IA, increasing on the Day 2 to 40-90% from the WI/IL border across the L.P. The powerful cyclone reaches peak intensity over the L.P. Friday night with MSLP in the low 970s making for very strong winds and a blizzard threat north and west of the low through this time. Strong northwest to west flow on the back side of the low envelopes the Great Lakes in the wake 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. Day 3 snow probs for >6" are 40-80% for typical NW and W snow belts. On the eastern side, cold air mass in place will slowly be eroded as broad southerly flow once again erodes 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 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 2.5 WPC snow probabilities for >6" are 40-80% over the Adirondacks and White Mtns. ....The West... Days 1-3... Active winter pattern continues over The West through this weekend. A positively-tilted trough digging down the Sierra Nevada early this morning crosses Arizona today and the southern Rockies this evening. Snow levels around 4000ft along the Mogollon Rim and north-central NM ranges along with decent Pacific-sourced moisture brings 40-80% Day 1 snow probs for >6" to these areas. A shortwave trough digging down British Columbia as it rounds a low over northern Alberta is the leading edge of the coldest air-mass of the winter season to date, reaching into the interior Northwest starting tonight and spreading across the Great Plains through Saturday. Northwesterly flow off the coast of British Columbia will strengthen as Alberta low and an expansive ridge extending north through Alaska funnel Pacific moisture into the Northwest and up the Columbia River Gorge today. With a strong dome of Arctic high pressure (possibly approaching record high pressure observations for the time of year in southwest Canada), a plume of moisture running into the boundary, and the added help of strong topographic ascent along ranges oriented orthogonally to the mean flow, heavy snow mountain snow is expected to develop across the southern WA through the OR Cascades into the northern Rockies today with snow levels generally 2000ft or less. Day 1 WPC PWPF shows high chances (>70%) for >12" of snowfall in the OR Cascades and Blue Mountains and moderate (around 50% for the ID Bitterroots to the Sawtooth. This focus shifts south through Friday before being reinforced by a ridge cutting shortwave trough that reaches the OR coast on Saturday with Day 2 probs expanded to even larger areas of the OR Cascades, Sawtooth and the Wasatch. A vorticity maximum shearing off from a long wave trough over the northeast Pacific will develop an area of low pressure that tracks towards Oregon coast Saturday morning. This wave will direct an atmospheric river to far southern OR through far northern CA Friday night with IVT values topping the 97.5 climatological percentile. With cold initial conditions from the Arctic air spreading south, heavy snow is expected at the onset with snow levels in northern CA initially around 3000ft before rising to 5500ft on Saturday. Day 3 PWPF for >8" is 50-80% over the OR Cascades, down the Sierra Nevada, across the ranges of the northern Great basin, the Wasatch, and the western CO Rockies. The warming onshore flow on Saturday looks to also cause a wintry mix over west-central OR where a glaze of ice is possible. Day 3 PWPF for >0.25" are 30-40% over the southern Willamette Valley west into the Coast Ranges. Jackson ***Key Messages for Jan 11-14 Major Winter Storm over the Midwest*** -High Confidence in Major Midwest Snowstorm Heavy snow is expected in the Midwest with a powerful winter storm. The greatest confidence in heavy snow exists in southern and eastern Wisconsin, and western and northern Lower Michigan, where over 12 inches of snow is likely (60-80%), causing considerable disruption. -Blizzard Conditions Possible with Strong Winds Strong winds will spread into the Midwest and Great Lakes on Friday and Saturday with the unusually powerful low pressure system. This will make blizzard conditions possible, particularly in exposed areas. Winds will increase on Friday night and the drastically reduced visibility will make travel dangerous to impossible. Wind gusts of 40 to 50 MPH may also lead to some power outages. -Lake Effect Snow Persists This Weekend While the larger area of snow will begin to diminish on Saturday, the arrival of colder air will generate heavy snow downwind of the Great Lakes this weekend. Winds will remain strong, posing a risk for significant blowing snow. -Flooding and Severe Storms in the South and East Severe thunderstorms will be possible Thursday and Friday in the Gulf Coast and Southeast. Another round of rain in the Mid-Atlantic and Northeast will lead to renewed rises on rivers and streams and possibly flooding. Moderate coastal flooding is also likely in the Mid-Atlantic and Northeast. ***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 will arrive in the northern Rockies and northern Plains Thursday night and Friday, before advancing farther south and east through much of the Plains and Midwest this weekend. Numerous daily cold records are likely in the south-central U.S. on Sunday, Monday, and Tuesday. -Dangerously Cold Wind Chills Expected At the peak of the Arctic outbreak early next week, minimum wind chills should fall below zero into Texas and the interior Southeast. Wind chills this weekend across the northern Plains and northern Rockies should be below negative 30 degrees. 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 Friday and Saturday Arctic air will gradually lower snow levels in time for the arrival of another storm system in the West on Friday. This may lead to snow and considerable impacts in valleys in Oregon, Idaho, Nevada, and Utah, including the Portland, Boise, and Salt Lake City metro areas. Freezing rain is likely Saturday in western Oregon. -Southern, Northeast Snow Early Next Week Snow is likely on the periphery of the advancing Arctic air mass from the interior South into the Mid-Atlantic Sunday into Monday and possibly over the Northeast into midweek. Stay tuned for further details. $$ --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (21:1/175) .