Subj : HVYSNOW: US Winter Storms To : All From : Dumas Walker Date : Fri Jan 05 2024 07:23 pm FOUS11 KWBC 052143 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 442 PM EST Fri Jan 05 2024 Valid 00Z Sat Jan 06 2024 - 00Z Tue Jan 09 2024 ....Southern Appalachians through New England... Days 1-3... Major winter storm to bring combination of freezing rain and heavy snow from the Southern Appalachians through New England. Overall, the forecast remains much the same with impactful ice expected along and east of the southern to central Appalachians into the Piedmont; followed by heavy snow impacting portions of the northern Mid-Atlantic and the Northeast. Low pressure now developing along the central Gulf Coast is forecast to move east through the overnight, directing moisture over an in-situ cold air wedge centered over the southern-central Appalachians/Piedmont. This will support the development of mixed precipitation across the area Saturday morning, with areas of significant icing still expected. WPC PWPF continues to show a solid stripe of at least moderate probabilities (greater than 40 percent) for ice accumulations of 0.10 inch or more extending along much of western North Carolina and Virginia, with the highest probabilities (greater than 70 percent) centered along and east of the Virginia Blue Ridge. Some of these areas may see accumulations exceeding 0.25 inch. As the system continues to evolve, with a deepening surface low forecast to move to the Delmarva coast by late Saturday, guidance continues to show heavy snow developing well northwest of the low within a left-exit upper jet region centered over the interior Mid Atlantic. The heaviest amounts through late Saturday are forecast to center over central Pennsylvania, where the WPC PWPF indicates that widespread accumulations of 4 inches are likely, with locally heavier amounts of 8 inches or more are possible. As the storm continues north along the Northeast coast it is expected to continue to strengthen ahead of an approaching shortwave moving across the eastern U.S. on Sunday Heavy snow will spread from the interior Mid Atlantic across much of interior southern to central New England. WPC PWPF shows at least moderate probabilities for accumulations of 8 inches or more extending from northeastern Pennsylvania to coastal Maine. Moderate probabilities for a foot or more extend from western coastal Maine back into the Worcester Hills of Massachusetts, as well as over portions of the Berkshires, Greens, and Catskills. ...Pacific Northwest/Great Basin/Sierra/Southwest.... Days 1-2... The region will remain active with an amplifying shortwave and an associated well-defined front moving into the Northwest on Saturday. Strong forcing, afforded in part by left-exit region upper jet forcing will support heavy precipitation along the Cascades, where snow levels are expected to drop below 2000 ft for much of the Washington and Oregon Cascades. Heavy accumulations well over a foot are likely across the favored higher peaks, with impactful amounts likely in the passes as well. WPC PWPF shows probabilities above 70 percent for accumulations of 8 inches or more falling within many of the major passes by late Saturday. The system will continue to amplify, carving out an anomalously deep 500 mb trough (2 to 3 standard deviations below normal) across the Southwest/Four Corners region by late Sunday. This will bring areas of heavy snow along the Sierra Nevada into the Great Basin and Southwest, along with a strong cold front pushing southeast across the region. In addition to the Sierra Nevada, areas impacted by heavy snow are expected to include the higher elevations of the central and northern Nevada mountains, northwestern Arizona southeastward along the Mogollon Rim to the White Mountains, and the Utah southwestern ranges. The WPC PWPF shows at least moderate probabilities (40 percent or greater) for accumulations of 6 inches or more across portions of these areas. Portions of the Sierra Nevada are likely to see some of the heaviest amounts, with a foot or likely for areas above 6000 ft. A well-defined ridge will follow the trough will dry conditions spreading across the Intermountain West and the Rockies on Monday. A warm front associated with an approaching shortwave will bring precipitation back into the Northwest on Monday. Snow levels will begin to increase but remain low at the onset, potentially bringing some additional impacts to the Cascade passes. ....Four Corners into the Southern/Central Plains... Days 2-3... A significant storm system is forecast to develop this Sunday (Day 2), initially taking shape over the Intermountain West as a digging 140 kt 300 mb jet results in vigorous upper-troughing and subsequent closed low formation over the Four Corners. Moderate to heavy mountain snows are expected to overspread the San Juans early Sunday beneath a focused region of left exit region forcing and accompanying height falls, with southwesterly 700 mb flow supporting appreciable moisture transport and orographic ascent with this system. The latest WPC snowfall probabilities of snowfall exceeding 4 inches sit squarely in the 80-90% range across the San Juans through this weekend, with 50-80% probabilities of exceeding 8 inches in the peaks of the terrain. As the ejecting closed low and lead shortwaves eject eastward into the Plains states, rapid leeside cyclonegenesis is expected to take shape by Monday (Day 3) with a rapidly expanding precipitation shield over the Heartland. An initial lead shortwave and focused area of low level WAA will support an initial bout of snowfall (with 40-50% probabilities of over 4 inches of snow) over portions of the Corn Belt early Monday morning along an inverted trough axis, while a focused axis of snowfall fills in upstream across the Central Plains along a deformation axis on the back side of the surface low. Guidance continues to differ somewhat as to the exact track of the surface low center, with ramifications for precip type and placement east of the Red River. However, there is a general consensus within the 12z deterministic guidance for a focused area of heavy blowing snowfall within the deformation axis across southwest Kansas into the Oklahoma/Texas Panhandle. The combination of enhanced snowfall rates and strong gradient wind within the rapidly intensifying system could result in blizzard conditions Monday over these areas, where the latest WSSI-P advertises a 40-50% chance of at least Moderate Winter Storm Impacts, primarily forced by blowing snow across portions of the Central/Southern High Plains through Day 3. Asherman/Pereira ***Key Messages for Jan 6-7 East Coast Winter Storm*** --Heavy Snow in the Northeast-- Expect heavy snow in interior portions of the northern Mid-Atlantic through New England Saturday afternoon into Sunday. There is a high chance (50-90%) of exceeding 8.. of snow from central Pennsylvania east through much of south-central New England. Local snowfall over 12 inches of snow is possible under the heaviest bands. --Impacts from Heavy, Wet Snow and Wind-- The combination of heavy, wet snow and gusty winds from northeast Pennsylvania through much of southern and central New England will result in difficult travel with some power outages and tree damage. --Minor Coastal Flooding Possible in the Northeast-- Gusty onshore winds may lead to minor flooding along the Mid-Atlantic and southern New England coasts during the Sunday morning high tide cycle. --Ice Impacts to Travel in Southern Appalachians-- The probability for ice accumulations in excess of 0.25.. along the Blue Ridge of North Carolina and Virginia are 30-50%. This icing, along with some areas of sleet, may produce hazardous travel conditions on tonight into Saturday. ***Key Messages for Jan 6-11 Major Winter Storm*** --Weather Impacts From Coast-to-Coast-- The next winter storm shifts down the West Coast Saturday crossing the Desert Southwest Sunday before rapidly strengthening over the southern Rockies/Plains Sunday night/Monday and then shifting through the Midwest/Northeast Tuesday/Wednesday. --Heavy Snow Expected; Blizzard Conditions Possible-- Expect heavy snow in the higher elevations near the West Coast and the Four Corners states this weekend before a swath of heavy snow develops over parts of the Southern/Central Plains Monday. Heavy snow then shifts through the Midwest Monday night and Tuesday. Given the intensity of the storm, strong winds may create areas of blizzard conditions over the Plains into the Midwest. --High Winds Ahead of the Storm-- Gusty winds on the warm side of the storm may exceed 50 MPH and cause damage over the Appalachians to the East Coast. Organized severe thunderstorms are possible along the Gulf Coast and Southeast Monday and Tuesday. --Flooding and Coastal Flooding Risk in the Eastern U.S.-- Heavy rain Tuesday into Wednesday is likely to lead to river and possibly flash flooding from the central Gulf Coast through the Northeast. Powerful onshore winds are also likely to lead to coastal flooding along much of the East Coast. $$ --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (21:1/175) .