Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Tue Dec 06 2022 Valid 12Z Fri Dec 09 2022 - 12Z Tue Dec 13 2022 ...Guidance/Predictability Assessment... The WPC medium range product suite was primarily derived from a blend of best clustered guidance from the 18 UTC GFS/GEFS and 12 UTC ECMWF/ECMWF ensemble mean along with WPC continuity and the 01 UTC National Blend of Models, applying the bulk of blend weights to the models Friday before transitioning to mostly ensemble means by early next week. ...Weather/Hazard Highlights... Organized upper shortwave trough passage and lead frontal moisture pooling may spread a swath of moderately heavy rains through the central Appalachians/Mid-Atlantic Friday, with coastal activity lingering this weekend with uncertain/moderate coastal low genesis. Some recent models show potential for a 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 some snow/ice during this period on the cooled northern periphery of this precipitation shield. Meanwhile upstream, ample system energies digging southeastward from the Gulf of Alaska are slated to continue to work across the West Coast into the West Friday and renew moderately heavy precipitation chances into the Northwest and California to include a threat for enhanced terrain/mountain snows that will spread over an unsettled and cooled Intermountain West/Rockies. System ejection then offer an emerging setup for moderate to heavy rainfall with some potential for runoff issues centered over the southern Plains and mid-lower MS/TN Valleys next weekend as western U.S. upper trough energies eject 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. The spread in the guidance has persistently been all over the place from run to run with system focus, especially after about 4/5 days into the forecast period, but the models have overall trended slightly toward amplification/less progression. Accordingly, downstream propagation of the main system out from the West into the east-central U.S. is delayed a bit early next week compared to continuity, but has potential for sufficient amplitude to support moderate cyclo/frontogenesis and a renewed return flow of Gulf moisture to support an expanding area of precipitation. NBM QPF seems overdone with coverage/amounts given uncertainties so targeted this for change, but there is nonetheless an emerging threat for heavier convective rains perhaps centered over the mid-lower MS Valley/Lower OH Valley. There is meanwhile also a threat for some snow/ice on the northern/northwestern periphery of the precipitation shield over the north-central U.S.. 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