Extended Forecast Discussion NWS Weather Prediction Center College Park MD 205 AM EST Tue Nov 09 2021 Valid 12Z Fri Nov 12 2021 - 12Z Tue Nov 16 2021 ...Robust Midwest/Great Lakes Low into later this week... ...Multiple rounds of precipitation into the Pacific Northwest later this week... ...Pattern Overview and Weather/Hazards Highlights... Anticipated flow transition will lead to development and passage of an amplified upper trough over the central to eastern U.S. Friday/Saturday as a potent surface low lifts northeastward through the Midwest/Great Lakes into eastern Canada. An attendant cold front will sweep eastward across the East, favoring a swath of moderate to locally heavy rain as fueled by long fetch moisture influx from the Gulf of Mexico and the western Atlantic. The progressive nature of the front may limit runoff threat, but the best potential may be over favored terrain of interior New England. Enhanced wrap-around then lake effect snows are expected from the Upper Midwest/Great Lakes and into the northern Appalachians/Northeast. Cold air and return moisture flow with another potent upper shortwave/surface system digging into the Midwest/Great Lakes onward on the heels of the lead storm will favor local snows across the region. Meanwhile upstream, another long fetch plume of Pacific moisture will feed into the Pacific Northwest, Friday into Saturday before easing. Subsequent rounding flow with embedded shortwaves may also support additional periods of enhanced precipitation later this period. Overall, 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 through this forecast period. Accordingly, the WPC medium range product suite was primarily derived from a composite blend of best clustered guidance from the GFS/ECMWF and GEFS/ECMWF ensemble means along with the National Blend of Models days 3-7 (Friday-next Tuesday). This strategy acts to maintain decent system depths and detail consistent with a pattern with near average predictability. WPC product continuity is also well maintained. 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