Extended Forecast Discussion NWS Weather Prediction Center College Park MD 250 AM EDT Fri Nov 05 2021 Valid 12Z Mon Nov 08 2021 - 12Z Fri Nov 12 2021 ...Guidance/Predictability Assessment... Models and ensembles show a reasonably similar larger scale pattern evoution aloft and overall precipitation focus through medium range time scales despite the transitory nature of the flow from onset of progression to somewhat more slowed and ampified flow. However, surface system forecast variance, uncertainty and continuity increases more significantly days 4-7 (Tuesday-Next Friday). While identifying synotic areas of activity, predictability of the local focus for heavier precipitation is limited outside of favored terrain of the West. Accordingly, the WPC medium range forecast package was primarily derived from a composite of the 18 UTC GFS and 12 UTC ECMWF/UKMET/Canadian only for day 3/Monday before rapidly transitioning to the compatible 18 UTC GEFS mean, the 12 UTC ECMWF ensemble mean and the 01 UTC National Blend of Models for days 4-7. The latest 00 UTC models continues to show above normal run to run continuity issues with embedded systems that given the lack of a strong signal for a particular solution, seems to lend creadance to the ensemble based forecast approach. ...Pattern Overview and Weather/Hazards Highlights... An amplified southern stream upper trough and deepened low off the East Coast will increasingly shift over the Atlantic Monday/Tuesday as a martime threat as a stable/warm upper trough extends upstream from the Southern Plains to the Northeast/East. Meanwhile, an uncertain series of lead Pacific systems will work inland across the West, with upper troughing set to work over the Northwest into midweek. This will highlight periods of terrain enhanced rainfall from the Pacific Northwest to central California and a heavy snow threat from the Cascades to the Sierra and inland across favored terrain for the north-central Great Basin/Rockies with cooling frontal passage. There is a trend in guidance that ejecting energies may dig into the central to east-central U.S. Wednesday-next Friday to carve out an amplified upper trough slated to be sandwiched between amplifying upper ridges over the West Coast and East Coast as the pattern transitions. Cyclogenesis and frontogenesis would act to favor an emerging lead rainfall/convective pattern over the east-central U.S. as thetae advection increases. Backside cold air flow also suggests potential for late next week snows over the Dakotas/Upper Midwest as moisture feeds back around a developing main low. Please see WPC links below for all the details. 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