Extended Forecast Discussion NWS Weather Prediction Center College Park MD 141 AM EST Tue Dec 01 2020 Valid 12Z Fri Dec 04 2020 - 12Z Tue Dec 08 2020 ...Guidance Evaluation/Preferences... Upper high over the Pacific Northwest will remain mostly in place atop an upper low over the Desert Southwest/Northwestern Mexico during the period. In the East, successive/reinforcing troughing will maintain an active pattern with several embedded systems. While the models/ensembles have generally been in agreement on the longwave configuration, they have struggled with the individual systems in timing/track/depth and evolution. Changeability in the ensemble means has led to no better than average confidence despite the happenstance agreement in the guidance for a given cycle. Thus, forecast philosophy continues to be to stay with a broad consensus that only discards the largest extremes. Through the 12Z/18Z guidance, the GFS/GEFS and ECMWF/ECMWF ensemble mean formed an adequate starting point to the forecast despite their differences in the evolution. Trended to just the ensemble means for next Mon/Tue as the deterministic solutions drifted farther apart. This favors low pressure over/near New England Sun-Tue via a lead and secondary system. ...Sensible Weather and Hazards... Precipitation will focus in the eastern 1/3rd of the CONUS, tied to the system in the Gulf late this week that lifts northeastward over the weekend. Rainfall could be light to modest, depending on how close the system tracks and how deep it may get. Best chance of heavier precipitation will be over the Northeast should the lead and secondary systems deepen close to the coast. Otherwise, a farther east track/development could lead to a rather dry pattern nearly CONUS-wide. Pacific Northwest will see an increase in clouds then rain along the coast by late in the period as a front moves closer. Any precipitation over the Southwest/southern Rockies due to the upper low is forecast to be light. Temperatures will be cooler than normal along the southern tier of the lower 48 with a cooling trend in the East behind the front and aided by a northern stream system. Milder than normal temperatures are forecast for the northern tier from Montana into the Upper Midwest. Readings could be 10-15 degrees above normal there. Fracasso Additional 3-7 Day Hazard 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