Extended Forecast Discussion NWS Weather Prediction Center College Park MD 212 PM EST Fri Nov 13 2020 Valid 12Z Mon Nov 16 2020 - 12Z Fri Nov 20 2020 ...Overview... The Pacific Northwest and portions of the West Coast will be in an active, wet pattern through the duration of the extended period as an eastern Pacific trough moves onshore. Downstream, the ridge will progress into the Plains and an amplified trough track across the East Coast early in the week. The Trough will pull offshore by the mid-week onward. ...Guidance Evaluation/Preferences... Model consensus was in decent agreement with the evolution of the deepening closed low/trough over the eastern Pacific Ocean. Like previous cycles, the CMC was slower which the resultant QPF for Vancouver Island and surrounding areas were several inches higher than other solutions. The UK was also slower this cycle. The 00Z ECWMF and the 00/06Z GFS were comparable with the the eastern Pacific trough moving onshore and the shortwave energy ejecting out of it. The GFS is favoring a further south placement of the mid/low-level low as it moves toward the West Coast and as such, the QPF extends further south as well. The ensemble means of both models help reduce the timing, magnitude and placement of specific details. Opted to maintain continuity in model preference by combining th ECWMF/GFS/GEFS mean/EC ensemble means with slightly more weighting of he means by he middle and later periods. ...Sensible weather and hazards... Onshore flow across the Pacific Northwest an California will bring moderate rains to the lower elevations an snow in the mountains. Precipitation intensity may become heavy at times, especially for portions of he Coastal and Cascade ranges. The nearly perpendicular flow over the terrain will result in enhanced lift and may result in periods of higher rainfall rates. As the storm deepens strong winds will accompany it. Some of the moisture will extend into the northern Rockies through the week and perhaps into the Northern Plains by next Friday. As the week progresses, the rain will trend light across the West. Elsewhere, some areas of precipitation will be possible to the lee of the upper-eastern Great Lakes during the first half of the week while some areas of mostly light precipitation may accompany the frontal system traversing the northern tier U.S. into New England mid-late week. A large portion of the western and central U.S. will see above to well above normal temperatures during the period. Greatest anomalies of plus 10-20F or slightly greater are most likely over the north-central through southern High Plains and over/near the Southwest. Best potential for some daily record highs should be over the Southwest. Expect the upper trough arriving from the Pacific and leading surface front to bring highs down to near or slightly below normal values by next Fri over the West Coast states and western Great Basin. Meanwhile some of the Plains warmth should extend into the Midwest/Ohio Valley late in the week, reversing an early-mid week episode of chilly weather over the East. Within this chilly period the best potential for double-digit anomalies may be on Wed when parts of the Mid-Atlantic/Northeast could see highs up to 10-15F below normal. Campbell 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 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