Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1058 AM EST Sat Dec 08 2018 Valid 12Z Tue Dec 11 2018 - 12Z Sat Dec 15 2018 ...Heavy rain threat for the east late next week... ...Overview and Guidance Evaluation/Preferences... The weather pattern is expected to remain quite active in the Pacific Northwest and become increasingly wet in much of the east later in the week next 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. Generally favored the deterministic models nearest the ensemble mean consensus and continuity which included the 00Z GFS/ECMWF. By next Fri/Sat, with upper ridging over Hudson Bay and deep troughing in the Bering Sea, teleconnections favor a closed low through the Tennessee and Ohio Valleys with a surface low track on the west side of the Appalachians toward the eastern Great Lakes. With a trend toward increased amplitude, favored the slower half of the solutions (i.e., 00Z GFS/ECMWF) as the ensemble trend has been slower overall the past several cycles. In the west, a blended solution should suffice downwind of a strong Pacific jet. ...Weather Highlights and Hazards... A departing coastal low off the Carolinas Tuesday offers a lingering maritime gale hazard being followed by OPC. In the wake of the low, cool temperatures and reinforcing dry high pressure will keep temperatures below average east of the Mississippi through midweek. Above average temperatures will outrun the lead and secondary Pacific systems through the Plains Tue-Thu before surging into the east Fri/Sat. Out West, precipitation and wind will periodically increase early-mid next week and into next weekend as heights fall with a succession of approaching shortwaves/frontal systems. Higher terrain of western Oregon/Washington have the potential for heaviest precipitation amounts (rain and mountain snow) as the systems move inland into the north-central Great Basin/Rockies. By late Wednesday into Thursday, secondary Pacific shortwave will dive through the Rockies into the southern Plains and overtake/reinforce upper troughing while spawning cyclogenesis at the surface over Oklahoma. Gulf moisture will increase ahead of the system helping to expand the precipitation shield to the east and then wrapped around to the north of the surface low. Relatively slow movement of the system will support a heavy rain threat and some cold sector snow through the Midwest/Great Lakes region to the northwest of the low track. Rainfall may be heavy along the east side of the Appalachians to the coastal plain with the infusion of Atlantic moisture as well, which could fall over areas that receive appreciable snowfall over the next couple of days (southern Appalachians). Fracasso 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