Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Wed Feb 20 2019 Valid 12Z Sat Feb 23 2019 - 12Z Wed Feb 27 2019 ...Excessive rainfall/flooding threat from the Lower Mississippi/Tennessee/Ohio Valleys to the Southern/Central Appalachians and a significant winter storm from the south-central Plains to the Upper Midwest/Great Lakes and interior New England this weekend... ...Pattern Overview and Weather Highlights/Hazards... Potent upper low/trough energy lifts northeastward this weekend from the southern Plains to the Northeast overtop an amplified and slow to erode Bahamas/Southeast U.S. upper ridge. This brings a threat for significant accumulating snow with some icing possible around an associated and deepening surface low with a pressure in the 980s by Sunday over the Great Lakes. This would likely result in gusty winds and potential blizzard conditions across the Upper Midwest and Great Lakes. Underneath, a multi-day heavy rain/training episode rejuvinates from the lower MS/TN/OH Valleys to the Southern/Central Appalachians Saturday, exiting the East Coast Sunday with frontal passage. Flooding/runoff issues will remain fueled by advection of highly anomalous moisture/warm air and deep cyclo/frontogenesis. SPC also shows a severe weather threat given system anomalous nature/vigor. A long-standing and wintry mean upper trough over the West will again be reinforced Sat-Mon as energy digs to the lee of a blocking Gulf of Alaska centered upper ridge. These systems will be less amplified than prior systems in this recent pattern, but will bring unsettled weather pattern through the Northwest and north-central Intermountain West and Rockies, with the best chance for accumulating snowfall over the Cascades. Guidance has not been very consistent recently with the evolution of the upstream flow next week, but now shifts the upper high/ridge northward over the Alaskan interior. This flattens and moderates flow into the West by Tue/Wed with emergence of undercutting but less certain southern stream Pacific flow and pattern with northern stream energy/height falls ejecting eastward over the n-central to northeastern U.S. This should keep the n-central U.S cold but also support system development that could lead to deeper development into the East in about a week. ...Guidance/Predictability Assessment and Preferences... Guidance is reasonably well clustered at mid-larger scales through much of the medium range period. WPC progs were primarily derived from a composite blend of the latest GFS/ECMWF and GEFS/ECMWF ensemble means. This maintains reasonable WPC continuity overall. Schichtel WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation and winter weather outlook probabilities are found 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