Extended Forecast Discussion NWS Weather Prediction Center College Park MD 158 AM EST Fri Nov 20 2020 Valid 12Z Mon Nov 23 2020 - 12Z Fri Nov 27 2020 ...Overview and Guidance Evaluation... The WPC medium range product suite was primarily derived from a composite blend of reasonably well clustered guidance from the 18 UTC GFS and 12 UTC ECMWF/Canadian days 3-4 (Mon-Tue) in a period of above normal overall predictability. Replaced the GFS in this composite with the 12 UTC ECMWF ensemble mean days 5-7. The ECMWF/Canadian and ECMWF ensemble mean seem reasonably well clustered days 5-7. The 18 UTC GFS/GEFS mean trended slower than previous runs overall, but still seemed too progressive/weak with southern stream upper level shortwave troughing from the Mid-South through the East Coast and also upstream with digging upper trough energies into the West. The 00 UTC GFS/GEFS mean trended toward the WPC composite blend and the 00 UTC ECMWF remains in line, bolstering forecast confidence. The 12/00 UTC UKMET and 00 UTC Canadian are not as in line however, so there are still some uncertainties to work out in the coming days. ...Sensible Weather and Hazards... A lead wave tracking northeastward from the OH Valley into the Northeast Mon will produce a swath of organized precipitation. Most of the precipitation should fall as rain, but parts of the moisture shield's northern periphery should contain some snow and wintry mix. For Tue-Thu, there is an increasing signal for a separated southern stream shortwave trough/low aloft and surface low pressure system to produce an episode of meaningful precipitation from the Southern Rockies/Plains northeastward through the East, Expect some snow will be possible this period from the upper Midwest to the upper Great Lakes under more northern stream impulse influence. Over the Northwest, it remains the case that progressive but energetic flow aloft will promote a wet period as a series of fronts approach/reach the region. There is good continuity for persistence of rain and higher elevation snow with highest totals over Coastal and Cascade Ranges and a secondary maximum into the Rockies. The supporting trough energies aloft early next weak may be followed by more flow separated/amplified systems mid-later next week that could dig organized precipitation into California, the Great Basin and then the Southwest. 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