Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1048 AM EST Wed Dec 12 2018 Valid 12Z Sat Dec 15 2018 - 12Z Wed Dec 19 2018 ...Significant precipitation for the Northwest... ...Overview and Guidance Evaluation/Preferences... A deep closed low will exit off the southern Mid-Atlantic coast late this weekend and take its frontal system into the Atlantic, paving the way for a dry period in the east early next week. The Pacific Northwest will remain quite active as several systems push into/through the region downstream of a strong 170kt+ central Pacific jet. The models and ensembles continue to differ on the timing/track of the embedded systems across the lower 48, but the ECMWF ensemble mean again seemed to be the best base of the forecast, followed by the 00Z ECMWF as they have been slower with the exiting closed low out of the Southeast than the GFS/GEFS (which have trended slower). This stayed close to WPC continuity with the progression of systems. ...Weather Highlights and Hazards... Southeastern/mid-Atlantic frontal system will exit the coast along with some locally heavier rain (mostly in the short range period) and perhaps some wintry weather in northern New England. Temperatures will generally be near to above average except over Florida behind the front this weekend and the Northeast early next week as a northern stream cold front passes through. Upstream, precipitation/wind substantially increases from coastal Washington to northern CA through the weekend with resurgence early-mid next week as a succession of energetic Pacific shortwaves/frontal systems pass through the region. Higher Pacific Northwest terrain will see the heaviest rain/mountain snow (with varying snow levels as temperatures rise and fall between each system), with snows then working to the north-central Great Basin/Rockies. While this activity remains concentrated within a pronounced northern stream flow, a separated southern stream trough will carve out over the Southwest U.S./northern Mexico around Tuesday. This associated surface system may tap western Gulf moisture midweek next week with an increase in rainfall along the Rio Grande. Fracasso/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