Extended Forecast Discussion NWS Weather Prediction Center College Park MD 149 AM EST Mon Dec 05 2022 Valid 12Z Thu Dec 08 2022 - 12Z Mon Dec 12 2022 ...Guidance/Predictability Assessment... The WPC medium range product suite was primarily derived from a blend of the 18 UTC GFS, 12 UTC ECMWF/Canadian and latest GEFS/ECMWF ensemble means along with the 01 UTC National Blend of Models. However, applied blend weights strongly toward reasonably clustered model guidance for Thursday and then slowly ramped up input from the ensemble means into the weekend and early next week amid steadily growing forecast spread and uncertainty. Usage of the ensemble means is more problematic than usual given the GEFS/ECMWF envelope of forecasts become more out of sync than normal later period from the east-central Pacific into the lower 48, with no clear signal to differentiate in a data sensitive pattern. Accordingly, pattern evolution predictability seems below normal from the weekend into early next week, mainly due to small to larger scale differences with aspects of the digging of trough energy into the West and subsequent downstream progression. Overall, the aforementioned forecast guidance strategy acts to maintain max WPC product continuity. The latest 00 UTC models offer quite poor run to run continuity and limited common trends from the weekend into early next week, further lowering forecast confidence in this period. ...Weather/Hazard Highlights... Ejection of energetic upper trough energies and lead frontal moisture pooling is expected to spread a swath of moderately heavy rains through the Ohio Valley states and central Appalachians/Mid-Atlantic Thursday/Friday, possibly aided Friday into Saturday by uncertain/moderate coastal low genesis. The models seem to reasonably show a potentially more ample QPF signature than the NBM given support, albeit with less than stellar run to run axis placement. There is also some potential for a swath of snow/ice during this period on the cooled northern periphery of this precipitation shield from the Midwest through the Northeast. Meanwhile upstream, ample system energies digging southeastward from the Gulf of Alaska are slated to work into the West Thursday/Friday and renew moderately heavy precipitation chances into the Northwest and northern California to include a threat for enhanced terrain/mountain snows that will spread over an unsettled West/Rockies. The pattern seems to then offer an emerging moderate setup for rainfall over the east-central U.S. next weekend into early next week as western U.S. upper trough energies work uncertainly downstream as return Gulf moisture intercepts a developing/wavy frontal system. The pattern also seems favorable for renewed moderately heavy precipitation including terrain/mountain enhanced snows inland into the Northwest/West again by next weekend as additional northeast Pacific system energies work inland into the unsettled region, but guidance remains all over the place from run to run with system focus and/or existence. 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, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml