Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1059 AM EST Mon Nov 04 2019 Valid 12Z Thu Nov 07 2019 - 12Z Mon Nov 11 2019 ...Pattern Overview and Guidance/Predictability Assessment... Latest guidance continues to show an amplified West Coast/Alaska ridge and east-central U.S. trough pattern that tends to have above average predictability for the large scale flow. However there are lower-confidence embedded details that will be important for resolving sensible weather effects over some areas. One significant difference involves potential surface development off the Northeast U.S. around day 4 Fri. Specifics of this feature are closely tied to the evolution/timing of a shortwave crossing the Upper Midwest/Great Lakes/Northeast Thu-Fri. Multiple ECMWF/CMC runs have depicted this system and the past 2-3 ECMWF mean runs capture it as well. Meanwhile the 00Z UKMET and GFS/GEFS mean are much farther east but the 06Z GFS/GEFS mean have adjusted westward closer to the ECMWF/CMC cluster. Overall preference follows a compromise among the past two ECMWF runs/00Z CMC with minority input from the 06Z GEFS/00Z ECMWF means. This maintains WPC continuity in representing a seemingly more plausible scenario given upstream ridge amplitude and baroclinic/dynamic environment to support development. Also teleconnections relative to the multi-day means' negative height anomaly center approximately between the Great Lakes and James Bay support increased precipitation potential over the Northeast. Short wavelength spacing and a distant Arctic/Alaska source region of the energy aloft--which tend to lower predictability--still keep confidence in specifics lower than desired. As for other issues, along the front that trails the above system the 00Z GFS becomes one of the more extreme western solutions for a wave off the southeastern coast by early day 5 Sat. This is due to a sharper shortwave aloft versus most other guidance. The 06Z GFS has trended eastward to agree better with remaining models/ensemble majority. By the latter half of the period there is a notable trend in the GFS/ECMWF and their means toward greater amplification/depth of the next shortwave digging into the long-term mean trough. This leads to faster progression of the next cold surge forecast to push into the central U.S. Also of note, the 00Z CMC and to some degree CMC mean erode the western ridge more than other solutions. This favors tilting the forecast toward the latest ECMWF/GFS runs and their means by days 6-7 Sun-Mon. ...Weather Highlights/Threats... To the west of the Rockies expect warm and mainly dry conditions. The one exception may be with a little Pacific moisture that could reach the northern Pacific Northwest terrain. Most locations will likely see highs 5-15F above normal through the period. The downstream pattern will favor periodic reinforcement of colder than normal temperatures from the Rockies and Central U.S. to the East as post-frontal high pressure centers track south/southeast from Canada. One cold airmass will cross the central/eastern states Thu-Sat with fairly broad coverage of highs 10-20F below normal and perhaps localized pockets colder than that, mainly on Thu-Fri. Then by Sun-Mon the next cold surge with highs 10-25F below normal should reach the central U.S. and begin to push eastward. One area of focused moisture will be along the front reaching into the South/East on Thu. Strong high pressure and sufficiently cold air behind the front may bring potential for some wintry precipitation into portions of the northeastern U.S. where amounts will be very sensitive to possible coastal/offshore low development by Fri. WPC Winter Weather Outlook graphics depict the probabilistic aspect of the forecast. Elsewhere, clipper systems and trailing cold cyclonic flow will bring periods of precipitation (mostly snow) to the Great Lakes/Northeast with activity prolonged by lake effect. Locations along the eastern slopes of the northern-central Rockies may see a period of snow as a front settles nearby. Any snow between these two areas should be fairly light and brief. Rausch/Schichtel 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