Extended Forecast Discussion NWS Weather Prediction Center College Park MD 127 PM EST Thu Nov 28 2019 Valid 12Z Sun Dec 01 2019 - 12Z Thu Dec 05 2019 ...Major Winter Storm will intensify over the Northeast Sunday night into Tuesday... ...Pattern overview and Guidance/Predictability Assessment... The medium range period (late Sunday through Thursday) begins with the deep cold core low over the southern Great Lakes. The low levels of this storm will be weakening/filling over the Midwest, but the mid/upper levels remain strong/cold. The surface low refocuses to the northern Mid-Atlantic coast Sunday night with rapid cyclogenesis then through Monday as the low stalls off the New England coast. The attendant cold front sweeps across the Mid-Atlantic and Southeast through Sunday night. The 00Z CMC remained an outlier as the fastest global guidance with this low and was thus greatly limited in the model blend. Otherwise there was excellent agreement among global deterministic guidance with the track of this low through Day 4. Differences remain with the timing of the low tracking through the Canadian Maritimes Tuesday night/Wednesday with the 06Z GFS a little slower than the rest of the deterministic guidance as well as the 06Z GEFS mean. Therefore, emphasis toward the ensemble means begins on Day 5. Meanwhile, an upper level low shifting south off the Northwest coast Sunday will remain off California through Tuesday/Day 5 before shifting inland sometime on Wednesday. The 00Z CMC is an outlier here too with a track much farther west. A non-CMC blend worked well through Day 5 with a focus on the ensemble means for the eastward ejection for Day 6/7 which are slower than the 00Z operational ECMWF. ...Weather Highlights/Threats... The major winter storm to start the period over the Upper Midwest will be weakening as its comma head precipitation shield crosses the Great Lakes. However, rapid low development off the southern New England coast Sunday night will refocus heavy wintry precipitation over much of the interior Northeast. A deformation band the tracks up interior New England Monday with some precipitation continuing Monday night as the upper portions of the storm pivots northeast/takes on a more negative tilt as further shortwave activity wraps around. Strong winds will accompany this storm over the Great Lakes and over the Northeast, making for difficult and hazardous travel across much of the region. Behind the cold front temperatures across the Southeast and up the Eastern Seaboard look to be 10 to 15 degrees below normal Monday and Tuesday before moderating through the midweek as a ridge builds in behind the low. In the West, another round of heavy precipitation affects central and northern California into Monday with heavy mountain snows expected and the heaviest rain along the coast. Locally heavy rain and mountain snow may also shift into Southern California and parts of the Southwest Tuesday night/Wednesday depending on when and how the low ejects east. A chilly Sunday across the interior West is expected under high pressure with temperatures generally 15 degrees below normal. Temperatures then moderate over The West except for over the Great Basin where high pressure lingers until the low shifts inland on Day 6/7. 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, Sun-Mon, Dec 1-Dec 2. - Heavy snow across portions of the Northeast, the Central Great Basin, the Mid-Atlantic, California, the Upper Mississippi Valley, the Central Appalachians, the Great Lakes, and the Southwest, Sun-Mon, Dec 1-Dec 2. - Flooding possible across portions of the Northern Plains. - Flooding occurring or imminent across portions of the Northern Plains. - Flooding likely across portions of the Northern Plains and the Southwest. - High winds across portions of the Central Plains, the Lower Mississippi Valley, the Northern Plains, the Great Lakes, the Middle Mississippi Valley, the Upper Mississippi Valley, the Southern Plains, and the Ohio Valley, Sun, Dec 1. - High winds across portions of the Northeast, Sun-Mon, Dec 1-Dec 2. - Much below normal temperatures over parts of the Central Great Basin, Sun, Dec 1. - High significant wave heights for coastal portions of the Great Lakes and the Upper Mississippi Valley, Sun, Dec 1. - High significant wave heights for coastal portions of the Northeast, Sun-Mon, Dec 1-Dec 2. 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