Extended Forecast Discussion NWS Weather Prediction Center College Park MD 254 PM EST Tue Feb 18 2020 Valid 12Z Fri Feb 21 2020 - 12Z Tue Feb 25 2020 ...Guidance/Predictability Assessment... The above normal agreement among the global guidance continues into this weekend for shortwave activity over the north-central CONUS and the closed low off CA. The divergence begins with the next trough approaching the Pacific Northwest Saturday night with the GFS/UKMET continuing to be more amplified and faster than the ECMWF/CMC. As a result the typical blend of 06Z GFS/00Z ECMWF/UKMET/CMC was used through Day 4 with increasing usage of the 06Z GEFS and 00Z ECENS ensemble means Days 5-7. ...Weather Pattern and Hazard Highlights... Strong high pressure will slowly drift east from the central CONUS Friday through Saturday which combined with the low off CA results in rather little precipitation coverage for the entire CONUS Friday. The CA low ejects east across the southwest Friday night, pushing onto the southern Plains Saturday night, bringing moisture and precipitation across southern California and the Four Corners states. There looks to be a brief period of enhanced rain and high elevation snow with this system over the Four Corners region. As height falls and the surface system continue eastward expect precipitation to develop over the Plains/Mississippi Valley this weekend and spread into the eastern states through early next week. Gulf of Mexico return flow will promote locally moderate to heavy rainfall over parts of the mid-lower Mississippi and Tennessee Valleys/southern Appalachians, areas that will be sensitive to additional rainfall given ongoing runoff issues. This will be a fairly warm system, but there is a risk for snow/ice on the northern periphery (particularly for the Northeast) of the growing precipitation shield as the ambient/cold high pressure dome recedes. Upstream, the upper trough/surface system moving into the West Saturday night/reaching the northern Rockies Sunday night will bring enhanced rain and higher elevation snow to the Pacific Northwest, with snows spreading into north-central portions of the Great Basin/Rockies/Plains with slow system progression and reinforcement. Much below normal temperatures spread east with the dome of high pressure Friday into Saturday. Temperatures of 10 to 15 degrees below normal are expected from the southern Plains to the Eastern Seaboard Friday and just the Southeast on Saturday. Temperatures will moderate across these areas through early next week. The system moving into the Northwest will bring below normal temperatures to most of the region Sunday into Monday, expanding to the Rockies/Plains Monday into Tuesday. 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 Pacific Northwest, Sun-Mon, Feb 23-Feb 24. - Heavy rain across portions of the Central 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, Sun-Mon, Feb 23-Feb 24. - Heavy snow across portions of the Pacific Northwest, the Northern Rockies, and the Northern Great Basin, Sun-Mon, Feb 23-Feb 24. - Heavy snow across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Southern Rockies, the Southern Plains, and the Southwest, Sat-Sun, Feb 22-Feb 23. - Flooding possible across portions of the Southeast. - Flooding occurring or imminent across portions of the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Mid-Atlantic, the Southeast, the Pacific Northwest, and the Ohio Valley. - Flooding likely across portions of the Southeast and the Ohio Valley. - 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, the Northern Great Basin, the Southern Plains, and the Southwest, Mon-Tue, Feb 24-Feb 25. - Much below normal temperatures across portions of the Southeast, the Mid-Atlantic, the Southern Appalachians, and the Tennessee Valley, Fri-Sat, Feb 21-Feb 22. - Much below normal temperatures across portions of the Northeast, Fri, Feb 21. 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