Extended Forecast Discussion NWS Weather Prediction Center College Park MD 257 PM EST Fri Feb 14 2020 Valid 12Z Mon Feb 17 2020 - 12Z Fri Feb 21 2020 1545 UTC Update... The forecast was updated to incorporate the latest guidance, including a 00Z ECMWF/06Z GFS blend during days 3-5 (Mon-Wed), and a gradual trend toward increased ECENS/GEFS ensemble mean weighting during days 6-7 (Thu-Fri). Overall, models continue to show relatively good consistency with respect to the most significant systems affecting sensible weather across the CONUS during the medium range. Resultant changes to the ongoing forecast were relatively minor. Ryan Previous Discussion (issued at 0713 UTC)... ...Guidance/Predictability Assessment... Model and ensemble forecast variability remains less than stellar aloft through medium range time scales, but actually offers much better continuity with surface feature evolutions and precipitation coverage. The WPC medium range product suite was primarily derived from a blend of the GFS/ECMWF and GEFS/NAEFS/ECMWF ensemble means along with the National Blend of Models. This composite solution acts to mitigate the less predictable timing/emphasis variance aloft without sacrificing lower atmospheric detail and weather focus as consistent with predictability. ...Weather Pattern and Hazard Highlights... A series of impulses digging to the lee of a eastern Pacific upper ridge will reinforce a western U.S. mid-upper level trough position and surface cold frontal passages into early next week to favor cold flow with swaths of moderate precipitation including a threat of heavy terrain enhanced snows from the Pacific Northwest inland across the Great Basin/Rockies. Less certain mid-upper level trough energies will progress downstream over the Plains to spawn cyclogenesis and frontogenesis along with an emerging lead threat of widespread precipitation with warm sector rains and snow/ice on the northern periphery across the Midwest/Great lakes/Northeast with advent of southeastward surging post-frontal arctic air. The main wavy front is expected to consolidate and push out across the central and eastern U.S. Tue/Wed. While this will act to push lead moderate precipitation into the western Atlantic by midweek, expect lingering focus will remain along a trailing frontal zone back across the southern U.S. tier into later next week as additional impulses progress over the region. This may include some threat of overrunning wintry precipitation into the cold post-frontal airmass from the southern Rockies/Plains and South to the southern Appalachians/Mid-Atlantic. Schichtel 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 Southern Rockies and the Southern Plains, Wed-Thu, Feb 19-Feb 20. - Heavy rain across portions of the Southern Plains, Wed-Thu, Feb 19-Feb 20. - Heavy rain across portions of the Southeast, the Mid-Atlantic, the Lower Mississippi Valley, the Southern Appalachians, and the Tennessee Valley, Mon-Tue, Feb 17-Feb 18. - Heavy snow across portions of the Great Lakes, and the Upper Mississippi Valley, Mon, Feb 17 and portions of the Northeast and the Great Lakes, Tue, Feb 18. - Heavy snow across portions of the Central and Southern Rockies, Mon-Tues, Feb 17-18. - Flooding possible across portions of the Southeast, the Lower Mississippi Valley, and the Southern Plains. - 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, the Ohio Valley, and the Tennessee 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 Southern Plains, and the Southwest, Tue-Thu, Feb 18-Feb 20. - Much below normal temperatures across portions of the Middle Mississippi Valley, the Great Lakes, the Upper Mississippi Valley, and the Northern Plains, Tue-Wed, Feb 18-Feb 19. - Heavy precipitation across portions of the Alaska Panhandle and southern mainland Alaska, Tue-Fri, Feb 18-Feb 21. - Heavy snow across portions of southern mainland Alaska, Mon-Thu, Feb 17-Feb 20. - Much below normal temperatures across portions of mainland Alaska, Mon, Feb 17 and Thu-Fri, Feb 20-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