Extended Forecast Discussion NWS Weather Prediction Center College Park MD 309 PM EST Wed Feb 05 2020 Valid 12Z Sat Feb 08 2020 - 12Z Wed Feb 12 2020 ...Heavy rain threat for parts of the Southern Plains/Lower Mississippi Valley to the Tennessee Valley next week... ...Overview and Guidance/Predictability Assessment... Upper pattern will shift next week toward western troughing and a resurgence of the subtropical ridge over Cuba. A lead shortwave over the Pacific Northwest Saturday will drop southward across the Great Basin Sunday, likely deepening into a closed low by Monday over southern California by early Monday. As this weakens and lifts northeastward next Tuesday into Wednesday, a heavy rain threat will expand over the Southern Plains/Lower Mississippi Valley to the Tennessee Valley along a stationary frontal boundary. Yet another shortwave is forecast to sink southward out of British Columbia around next Tuesday into the Northwest, reinforcing the western trough. A deterministic blend (06Z GFS and 00Z ECMWF/CMC/UKMET) worked well for the Sat-Mon period with some lingering timing/location differences in the upper trough. Uncertainty increased by the end of the period with the evolution of the system in the Southwest (how quickly it may lift northeastward and weaken) as well as the northern stream flow over southern Canada through the Northeast. Favored a majority ensemble mean blend (06Z GEFS mean and 00Z ECMWF ensemble mean) along with continuity for next Tue/Wed. Confidence remains above average in the overall pattern, though details remain expectedly less clear by next week. ...Weather/Hazard Highlights... A weak system crossing the Appalachians this weekend may lay down minor accumulating snow over parts of the southern/central Appalachians Saturday into Sunday before moving offshore. Weak high pressure will settle into the Northeast on Sunday before another front from the Great Lakes moves into the region Monday. This may bring a band of accumulating snow to parts of the Upper Midwest Sunday. Several frontal systems out of the Northeast Pacific will bring modest to possibly heavy snowfall to the mountains of the Pacific Northwest into the northern/central Rockies on Saturday. As the western front sinks southward through the West, rain and mountain snow will push through California and the Great Basin. Light to modest amounts are possible over southern California through the deserts and into the Four Corners region. By early next week, as the upper low moves through the Southwest and ridging increases over the Gulf, a frontal boundary will settle across the mid-Mississippi and Tennessee Valleys. Gulf moisture will increase initially into the Southern Plains/Lower Mississippi Valley Monday and then spread northward and eastward into the Tennessee Valley by Tuesday into Wednesday along the frontal boundary. Convectively-enhanced rainfall supports a locally heavy rain threat in these areas. Some snow is possible on the northern edge of the precipitation shield from the mid-Mississippi Valley to the Midwest, but temperatures will likely be marginal. Temperatures in the East will trend milder/warmer through the period, with daytime highs 5 to 15 degrees above average returning by the middle of next week. Out West, cooler temperatures will settle into the area as troughing moves through the region. The Central U.S. should stay near average through the entire period. Fracasso 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 Pacific Northwest and the Northern Great Basin, Sat, Feb 8. - Heavy precipitation across portions of the Pacific Northwest, Mon-Tue, Feb 10-Feb 11. - Heavy rain across portions of the Southern Plains, the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, the Southern Plains, and the Ohio Valley, Mon-Wed, Feb 10-Feb 12. - Heavy snow across portions of the Central Plains, the Central Great Basin, the Northern Plains, the Northern Rockies, the Central Rockies, and the Northern Great Basin, Sat, Feb 8. - Flooding possible across portions of the Southeast, the Southern Appalachians, the Mid-Atlantic, the Northeast, and the Central Appalachians. - Flooding occurring or imminent across portions of the Lower Mississippi Valley, the Pacific Northwest, and the Northern Plains. - Flooding likely across portions of the Pacific Northwest. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Sat, Feb 8. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Sun, Feb 9. - High winds across portions of mainland Alaska and the Aleutians, Sat-Mon, Feb 8-Feb 10. 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