Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1128 AM EST Mon Nov 08 2021 Valid 12Z Thu Nov 11 2021 - 12Z Mon Nov 15 2021 ...Robust Midwest/Great Lakes Low into later this week... ...Multiple rounds of precipitation into the Pacific Northwest later this week... ...Pattern Overview... Upper ridging to the southwest of California as well as over the Canadian archipelago favors amplified troughing over the central to eastern CONUS later this week into the weekend. This favors a deepening central states cyclone that will lift northeastward through the Midwest/Great Lakes into Canada Thu-Sat. Milder air over much of the Lower 48 will trend cooler with time as the attendant cold front sweeps eastward, favoring a widespread swath of modest to locally heavy rain across much of the East. Within the western half of the low pressure area, wrap-around and then lake effect snow is likely over the Dakotas/Upper Midwest/Great Lakes late week and then the central/northern Appalachians. Upstream, there is a growing guidance signal bringing a long fetch plume of Pacific moisture into the Pacific Northwest, especially later this week. Favorable flow should focus heavy rains and elevation snows over the Olympics and Cascades. ...Guidance/Predictability Assessment... Guidance continues to illustrate a reasonably similar larger scale pattern evolution and forecast clustering has improved slightly Thu into Fri. A composite blend of the GFS/ECMWF/Canadian/UKMET seems reasonable, is in line with the NBM and GEFS/NAEFS/ECMWF ensemble means and maintains good WPC continuity in this time frame. However, the 00z Canadian and UKMET guidance become flatter and appear to retrograde the Western ridge into the Pacific, which by the end of the period leaves them verging on being completely out of phase with the other guidance. Given uncertainty in recent trends, the WPC product suite was derived from a composite blend of compatible guidance from GFS/ECMWF/NAEFS/ECMWF ensembles/National Blend of Models (with the NBM removed from QPF consideration late in the period). ...Weather/Hazards Highlights... Amplifying upper pattern will support surface cyclogenesis over the Upper Midwest into Thu as Gulf moisture streams northward along and ahead of the cold front, enhancing rainfall from the southern Appalachians northward into the Northeast. As the system moves into Canada, backside cold air flow by next Friday will likely support some snow within the system's comma head over the Dakotas/Upper Midwest/Great Lakes and subsequently with cold flow off the lakes and into the northern/central Appalachians. This could be the first accumulating snow of the season for some areas of northern Minnesota into the eastern Dakotas. Temperatures will be near to above normal early in the week, with possible record highs ahead of the front on Friday in the Mid-Atlantic, but trending cooler by week's end especially into the Southeast (relative to typical mid-November values there). Upstream, there is a growing guidance signal bringing several rounds of rain and mountain snow to the Pacific Northwest, especially later this week. Favorable flow should focus heavy rains and elevation snows over the Olympics and Washington Cascades. Roth/Schichtel Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook 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