Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1207 AM EST Sun Dec 09 2018 Valid 12Z Wed Dec 12 2018 - 12Z Sun Dec 16 2018 ...Heavy rain/wrapped snow threat into parts of the eastern U.S. late week... ...Overview and Guidance Evaluation/Preferences... The weather pattern this week is expected to remain quite active across the Northwest and become increasingly wet for much of the eastern third of the nation later week. The models continue to waver in the details in an otherwise rather predictable longwave upper pattern that is well-represented in the latest ensemble means. Accordingly, the WPC medium range product suite was primarily derived from a composite blend of the compatable latest GEFS/ECMWF ensemble means and continuity, with modest weighting applied to the latest GFS/ECMWF. ...Weather Highlights and Hazards... Precipitation/wind periodically increases into the Northwest midweek and again into next weekend as heights fall with a succession of approaching shortwaves/frontal systems. Higher Pacific Northwest terrain will observe the heaviest rain/mountain snow, with activity then working to the north-central Great Basin/Rockies with system advance. By Thursday, lead Pacific shortwave energy dives from the Rockies to the southern Plains to reinforce upper troughing while spawning surface cyclogenesis. Gulf moisture/warm advection increasing ahead of the deepening system helps to expand the precipitation shield to the east and wrapped around to the north of the surface low. Relatively slow movement of the system will support a heavy rain threat and cold sector snows through the Midwest/Great Lakes and interior Mid-Atlantic/Northeast mainly to the northwest of the uncertain low track. Rainfall may be heavy from the east side of the Appalachians to the coastal plain with the infusion of Atlantic moisture as well, which may fall over areas receiving appreciable weekend snowfalls, especially over the southern Appalachians. Schichtel WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes 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 https://www.wpc.ncep.noaa.gov/heat_index.shtml