Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Sat Nov 06 2021 Valid 12Z Tue Nov 09 2021 - 12Z Sat Nov 13 2021 ...Pattern Overview and Guidance/Predictability Assessment... An amplified upper trough/low and deepened surface low offshore the Southeast should increasingly exit over the Atlantic early next week as a stable and warm upper ridge extends from the southern Plains to the East. Meanwhile upstream, an upper low will rotate through the Gulf of Alaska/northeast Pacific and ejecting lead shortwaves will traverse the West/Rockies, propagating eastward through the north-central states to the Northeast in progressive flow to limit precipitation. Main Pacific upper trough energy working over the West/Rockies Tuesday into Wednesday is still then slated to amplify over the central to east-central U.S. mid-later next week and initiate lead surface cyclogenesis and frontogenesis in an emerging wet pattern to spread across the broad region and into the East. The latest suite of guidance continues to illustrate a reasonably similar larger scale pettern evolution, but plenty of uncertainty in the details, timing, and strength of systems. Right off the bat, the GFS remains different with the exiting Southeastern U.S. trough, showing more defined northern/southern stream separation and a stronger/more south surface low well off the coast. Bigger issues/uncertainties arise later period as troughing amplifies over the Central U.S. with some guidance showing closed upper low development by Thursday/Friday next week. Run to run variability suggests models struggle with this feature, but flow amplitude should bring at least a defined low pressure system into the Midwest by late next week. Accordingly, the WPC medium range product suite was primarily derived from a composite blend of reasonably compatible guidance from the 18 UTC GEFS mean, 12 UTC ECMWF ensemble mean, the 01 UTC National Blend of Models and manual adjustments to ensure a bit more detail consistent in areas with better forecast clustering broad support. This plan acts to maintain good WPC product continuity. ...Pattern Overview and Weather/Hazards Highlights... A series of Pacific systems will work inland across the West, with main upper troughing set to work through the region by midweek. This will favor 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 a cooling frontal passage. Subsequent amplified upper troughing carving out over the central U.S. is slated to be sandwiched between upper ridges over the West Coast and East Coast with pattern transition. Cyclogenesis and frontogenesis would act to favor an emerging lead rainfall/convective pattern over the east-central U.S. as theta-e 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