Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 PM EST Fri Dec 13 2019 Valid 12Z Mon Dec 16 2019 - 12Z Fri Dec 20 2019 ...Wintry weather threat early next week from the Ohio Valley to the Northeast..with heavy rain over parts of the interior Southeast... ...Pattern Overview and Guidance/Predictability Assessment with Weather Highlights/Threats... A low pressure system will track from the Lower Mississippi Valley on Monday into the Northeast on Tuesday. This should be a quick moving system so lingering and significant effects are not expected, though a swath of wintry precipitation is possible from parts of the Ohio Valley, through the northern/interior Mid-Atlantic, and into parts of New England. Models have come into better agreement with the setup and track of the low, though the GFS continues to be faster than the best consensus. Along the attendant cold front, areas of heavy rainfall are also likely across the interior Southeast/Tennessee Valley. SPC also highlights a 15% probability area for severe thunderstorms Monday across the Lower Mississippi Valley. The air mass behind the system will not be tremendously cold, although much of the eastern two-thirds of the country will be colder than normal through the middle of next week. Meanwhile, models indicate that a Pacific cyclone will approach the West Coast by about Wednesday of next week. The GFS again shows a faster forward motion with this system and weaker/flatter downstream ridging across the Four Corners region. The ensemble means also support the faster GFS, and even though the ECMWF is notably slower/stronger with this system, it has support from the CMC and the UKMET (through day 5), along with good run-to-run continuity so it does not seem totally unreasonable. Given the uncertainty though, a blend closer to the ensemble means was a good starting point, and fit well with previous WPC continuity. Precipitation ahead of this cyclone should first reach California and the Pacific Northwest on Wednesday, with slow inland progression. Snow is possible in the higher elevations, with potentially heavy snowfall in the Cascades late next week. Depending on how quickly the trough ejects into the Southwest, return moisture out of the Gulf of Mexico may also begin impacting parts of South Texas next Friday. Santorelli/Kong 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 - Heavy precipitation across portions of California, and the Pacific Northwest, Thu-Fri, Dec 19-Dec 20. - Heavy precipitation across Ohio Valley, the Mid-Atlantic, and the Northeast, Mon-Tue, Dec 16-Dec 17. - Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Fri, Dec 20. - Heavy rain across portions of the Lower Mississippi Valley, the Southeast, and Central Appalachians, Mon-Tue, Dec 16-Dec 17. - Heavy snow across portions of the Mid-Atlantic and Northeast, Mon-Tue, Dec 16-Dec 17. - Severe weather across portions of the Lower Mississippi Valley and the Southeast, Mon, Dec 16. - Flooding occurring or imminent across portions of the Northern Plains. - Flooding likely across portions of the Northern Plains. 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