Extended Forecast Discussion NWS Weather Prediction Center College Park MD 156 PM EST Mon Dec 05 2022 Valid 12Z Thu Dec 08 2022 - 12Z Mon Dec 12 2022 ...Guidance/Predictability Assessment... The overall pattern for the next week will be transitioning from a West Coast trough/Southeast ridge to a more broad trough with a generally southwest flow regime across the CONUS. However due to the degree of spread with the timing, location, and amplitude differences shortly after the initial period, confidence in any of the specifics is below average. The WPC medium range product suite was primarily derived from a blend of the ECWMF/GFS with lesser weighting of the CMC/UKMET to start and as the time goes on the inclusion and weighting of the ECWMF ensemble/GEFS means were increased- ending the with 50% means/50% deterministic by the end of the forecast. This helped maintain continuity and reduce the noise within the guidance. Additionally, it led to a bit of a slow down in the frontal progression across the central CONUS for Days 5-7 when compared to the previous forecast. As previously noted, the 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. ...Weather/Hazard Highlights... Energetic impulses are expected to eject from the upper-level trough across the central U.S and with lead frontal moisture pooling will spread a swath of moderately heavy rains through the Ohio Valley states and central Appalachians/Mid-Atlantic Thursday and Friday. It may linger 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. Some of the rains moving across the Tennessee/Ohio Valleys through Friday morning, have increased soil saturation from recent rainfall, may reach or exceed local flash flood guidance and see isolated areas of flash flooding. The elevated risk for runoff and flash flooding will shift to portions of the Appalachians and the Delmarva region into Saturday morning as the area of rain shifts eastward. 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. The spread in the guidance has persistently been all over the place from run to run with system focus and/or existence. The rainfall amounts and location of this precipitation may change significantly over the next few days as the models work out various issues. Campbell/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