Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Sun Dec 04 2022 Valid 12Z Wed Dec 07 2022 - 12Z Sun Dec 11 2022 ...Heavy rain threat from the southern Plains to the Mid-South midweek to the central Appalachians/Mid-Atlantic later week in active flow across much of the nation... ...Guidance/Predictability Assessment and Weather/Hazard Highlights... The WPC medium range product suite was primarily derived from a composite of reasonably well clustered guidance from the 18 UTC GFS and 12 UTC ECMWF/UKMET/Canadian models along with WPC continuity and the 1 UTC National Blend of Models for Wednesday into Friday in a pattern with seemingly improving/above average predictability. The latest 00 UTC model runs generally remain in line as well during this forecast period. There is a growing signal for heavy rains from the southern Plains to the Mid-South midweek with ejection into the flow of southern stream upper trough and the experimental medium range WPC Excessive Rainfall Outlook (ERO) continues to have a "Slight" risk area centered over the region as also fueled by frontal pooling Gulf moisture/repeat cells within the favorable right entrance region of the upper jet. Activity may spread ENEWD to the central Appalachains/Mid-Atlantic into Thursday/Friday, possibly aided Friday by uncertain/moderate coastal flow genesis. 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 should spread increasingly inland over an unsettled West into the weekend. Transitioned model guidance increasingly toward the GEFS/ECMWF ensemble means next weekend in a period with quickly growing model forecast spread that is mainly due to differences with aspects of the digging of energy into the West and subsequent downsteam progression. However, suspect the means are by nature are not amplified enough given recent flow history and model trends, so still incorporated into the forecast limited model guidance to compensate and provide better system detail as warranted. The pattern also looks to offer another emerging favorable setup for additional rainfall over the east-central U.S. next weekend 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 precipitation into the Northwest again next weekend as additional northeast Pacific system energies work inland into the unsettled region. 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