Extended Forecast Discussion NWS Weather Prediction Center College Park MD 321 PM EST Wed Nov 27 2019 Valid 12Z Sat Nov 30 2019 - 12Z Wed Dec 04 2019 ...Major Winter Storm will track from the Northern Plains to the Northeast Saturday through Monday... ...Pattern overview and Guidance/Predictability Assessment... The medium range period (later Saturday through Wednesday) begins with a developed low over the north-central low pressure system as the low over The West shifts east, merging into the shortwave through that had been wrapping around and tracking through the Desert SW. This newly developed phase of this major winter storm then shifts east across the southern Great lakes through Sunday. Additional southern stream shortwave energy rounding the base of this cold core upper low allows for a new surface low to form off the northern Mid-Atlantic coast Sunday night which then tracks up the New England Coast through Monday. A notable difference in the latest guidance with the low track on Day 3/Saturday. The GFS continues to bring the system farther northwest, well into South Dakota while the consensus low is closer to the South Dakota/Nebraska border at 12Z Saturday. The cause of this track difference in the GFS appears to be a combination of a stronger shortwave coming in from the Southwest that is a bit ahead of the consensus and allows a track farther to the northwest. This low position has notable implications for where the warm sector develops and thus precipitation type. As a note on this low track, the swath of snow across the central Plains to Lake Superior may affect the low level temperature gradient and thus the exact track of the low, though probably more Saturday night as the low moves over IA. WPC pressures/fronts/temperatures/precipitation did incorporate the 06Z GFS in a blend with the 00Z ECMWF/UKMET/CMC through Day 5. There are further uncertainties with the exit of the low off New England on Day 6 with the GFS now closer to the New England coast on Tuesday. Therefore ensemble means were heavily weighed on Days 6/7, leaning toward the 00Z ECENS. The next low approaches The West Coast Saturday and wobbles nearer and farther from the coast as it drifts south to a point off southern California by the middle of next week. The ECMWF continues to have decent run-to-run continuity with this system while the 06Z GFS resembles the 00Z ECMWF enough to warrant those models being the focus of a model blend for that region. ...Weather Highlights/Threats... A major winter storm with widespread hazardous weather is expected for parts of the Central and Eastern U.S. over the Thanksgiving holiday weekend through Monday. To the north and west of the surface low, heavy and significant accumulating snow is likely from the Dakotas to the Upper Great Lakes Saturday into Sunday. Precipitation then focuses to the developing coastal low Sunday night through Monday with the risk for accumulating currently farther inland over New England. High winds will also accompany this storm, making for difficult and hazardous travel across much of the region. To the south, locally heavy rainfall is possible along the attendant cold front as it shifts eastward across the Deep South/Ohio Valley/Mid-Atlantic states this weekend. Severe thunderstorms are also possible across the Lower Mississippi Valley on Saturday as indicated by the latest Day 4 SPC severe outlook. Another round of heavy precipitation affects California mainly Saturday night through Monday as the offshore low brings onshore flow. Expect mountain snows in northern and central California, with rain in the lower elevations. As of now a wobble back toward the southern California coast Tuesday night into Wednesday would bring rain and high elevation snow to southern California. Temperatures remain cold across The West through Sunday with daytime highs 10 to 25 degrees below normal over much of the Great Basin, Rockies into the High Plains. This shifts to the eastern states Monday with high temperatures generally 10 to 15 degrees below normal which replaces weekend above normal temperatures (generally 10 to 20 degrees above normal over the central CONUS on Saturday). Anomalies moderate through the midweek as ridging develops over the west-central CONUS. 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 rain across portions of California, Sat-Mon, Nov 30-Dec 2. - Heavy snow across portions of the Central Great Basin, California, and the Southwest, Sat-Mon, Nov 30-Dec 2. - Heavy snow for parts of the Central Plains, the Great Lakes, the Upper Mississippi Valley, and the Northern Plains, Sat, Nov 30. - Heavy snow across portions of the Great Lakes, the Mid-Atlantic, the Northeast, the Central Appalachians, and the Upper Mississippi Valley, Sun-Mon, Dec 1-Dec 2. - Severe weather for parts of the Southeast, the Lower Mississippi Valley, the Southern Plains, and Tennessee Valley, Sat, Nov 30. - Flooding occurring or imminent across portions of the Northern Plains. - Flooding likely across portions of the Northern Plains. - High winds across portions of the Plains, the Central and Southern Rockies, the Central Great Basin, the Great Lakes, the Mississippi Valley, the Ohio Valley, and the Southwest, Sat-Sun, Nov 30-Dec 1. - Much below normal temperatures across portions of the Central Great Basin, the Northern Rockies, California, the Northern Great Basin, the Pacific Northwest, and the Southwest, Sat-Sun, Nov 30-Dec 1. - High significant wave heights for coastal portions of the Great Lakes and the Upper Mississippi Valley, Sat-Sun, Nov 30-Dec 1. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Sun-Tue, Dec 1-Dec 3. 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