Extended Forecast Discussion NWS Weather Prediction Center College Park MD 158 PM EST Tue Nov 26 2019 Valid 12Z Fri Nov 29 2019 - 12Z Tue Dec 03 2019 ...Major Winter Storm Crosses Country Thanksgiving Weekend... ...Pattern overview and Guidance/Predictability Assessment... A deep cold core low centered over the Great Basin early Friday shifts east across the rest of the CONUS through Monday, potentially lingering near New England through Tuesday. Shortwave energy rounding the base of the low ejects northeast from the Desert SW Friday, reaching the north-central Plains Friday evening. Surface low pressure develops in the lee of the CO Rockies Friday and rapidly strengthens as it shifts northeast to South Dakota Friday night. The shortwave energy wraps into the parent low over South Dakota Saturday with the system turning east which reaches them crosses the southern Great Lakes before reaching the northern Mid-Atlantic coast Sunday night. There is a risk for further southern stream energy to wrap in with new surface low development along the Mid-Atlantic coast up to the New England Coast through Monday. The next low/trough approaches shifts southeast off The West Coast this weekend with multiple rounds of energy shifting this system south off or near the coast through the early part of next week. 00Z/06Z deterministic guidance was in good agreement (except for the 00Z UKMET noted below) with both systems and associated ridges through Day 5 before timing differences on the low tracking up the northeast coast. The 00Z UKMET remained slower with the ejection of shortwave energy over the Desert SW on Day 3 which leads to outlier placement of associated features and precipitation, so it was excluded from the medium range model blend which favors the 00Z ECMWF and 06Z GFS for Days 3-5. The 06Z GFS remained farther east/more progressive with the low off New England for Days 6/7 than the 00Z ECMWF, while the mean trough axis in the 06Z GEFS and 00Z ECENS is similar. Therefore the heaviest weight for Days 6/7 were with the ensemble guidance. ...Weather Highlights/Threats... Widespread hazardous weather is expected as the low ejects across the country through the Thanksgiving holiday weekend. Heavy, rather low elevation mountain snows are expected Friday into Saturday for much of the Central and Southern Rockies. As the surface low moves and rapidly develops into the northern Plains, a swath of heavy and rather significant accumulating snow is likely north and west of the low on the Plains from eastern Montana/northeastern Wyoming across the Dakotas to the Upper Great Lakes through Saturday night. The focus then shifts to the developing coastal low off the Mid-Atlantic Sunday night, continuing up the New England coast into Tuesday. High winds look to accompany all phases of this system making for difficult and hazardous travel across much of the region. Along and ahead of the attendant cold front, locally heavy rainfall is likely from the Southern Plains/Gulf Coast to the Ohio Valley. The latest SPC severe weather outlook has a 15 percent chance of severe weather for Friday across the Southern Plains, shifting southeast to the west-central Gulf coast with another 15 percent chance of severe weather for Saturday. Notable temperature anomalies are expected with the system crossing the country. Cold air will focus across The West through the weekend with daytime highs 15 to 25 degrees below normal spreading east from the Great Basin Friday into the lee of the Rockies Saturday. A sweeping cold front crossing the country through Sunday night spreads below normal temperatures (generally 10 degrees or so below normal). Temperatures will be above normal (max temperatures 10 to 15 degrees above normal) over the southern Plains and Midwest Friday/Saturday ahead of the cold front. Jackson Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: - Heavy precipitation across portions of the Central Great Basin, California, and the Southwest, Sat-Mon, Nov 30-Dec 2. - Heavy rain across portions of California, Sat-Mon, Nov 30-Dec 2. - Heavy rain across portions of the Central Plains, the Lower Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Middle Mississippi Valley, the Southern Appalachians, the Southern Plains, and the Ohio Valley, Fri-Sun, Nov 29-Dec 1. - Heavy snow across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Northern Plains, the Northern Rockies, the Southern Rockies, the Northern Great Basin, the Southern Plains, and the Southwest, Fri-Sat, Nov 29-Nov 30. - Heavy snow across portions of the Central Plains, the Great Lakes, the Upper Mississippi Valley, and the Northern Plains, Fri-Sun, Nov 29-Dec 1. - Heavy snow across portions of the Mid-Atlantic, the Northeast, and the Great Lakes, Sun-Mon, Dec 1-Dec 2. - Severe weather across portions of the Central Plains, the Lower Mississippi Valley, and the Southern Plains, Fri, Nov 29. - Severe weather across portions of the Lower Mississippi Valley and the Southern Plains, Sat, Nov 30. - Flooding occurring or imminent across portions of the Northern Plains. - High winds across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Northern Plains, the Southern Rockies, the Middle Mississippi Valley, the Upper Mississippi Valley, the Southern Plains, and the Southwest, Fri-Sun, Nov 29-Dec 1. - High winds across portions of the Great Lakes and the Upper Mississippi Valley, Sun-Mon, Dec 1-Dec 2. - Much below normal temperatures across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Northern Plains, the Northern Rockies, the Southern Rockies, California, the Northern Great Basin, the Pacific Northwest, and the Southwest, Fri-Sun, Nov 29-Dec 1. WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml