Extended Forecast Discussion NWS Weather Prediction Center College Park MD 252 AM EDT Wed Oct 06 2021 Valid 12Z Sat Oct 09 2021 - 12Z Wed Oct 13 2021 ...Guidance Evaluation/preferences... The WPC medium range product suite was primarily derived from a composite model and ensemble blend days 3-7 with the 18 UTC GFS/GEFS Mean 12 UTC ECMWF/ECMWF ensemble means and the 01 UTC National Blend of Models prominantly weighted along with WPC continuity. Guidance forecasts are overall reasonably well clustered with the mid-larger scale pattern evolution into next week, bolstering forecast confidence to a degree, but tempered by continued run to run variability with the details and timings of a multitude of complex embedded systems in two streams. A composite of the latest 00 UTC model and ensemble suite still seems in line with this forecast plan. In particular, the 00 UTC UKMET has trended in this direction versus an outlier 12 UTC earlier run. ...Pattern Overview and Weather/Hazards highlights... While a lingering rainfall axis will continue into the weekend from the Mid-Atlantic/Central Appalachians to the Great Lakes, the focus this weekend into next week should shift to the coast/offshore where a frontal boundary and area of low pressure, with limited tropical development probabilities, could bring some heavy downpours to portions of the coastal Mid-Atlantic/Southeast. Upstream, a front lifting through the north-central U.S. will bring moderate to locally heavy rainfall to parts of the northern Plains/Upper Midwest this weekend. Amplified approach of southern stream upper trough energy underneath over the south-central Plains and Mid-Lower MS Valley should act to focus moisture/instability to fuel an increasingly favorable convection environment Sun/Mon, lifting and shearing over the Midwest/Great Lakes Tue. Out West, moderate to heavy rainfall and mountain snow is possible across parts of the Pacific Northwest this weekend, with moisture shifting southward and inland with a wavy/lead front. Deep troughing and closed upper low development down over the Southwest/Great Basin into early-mid next week will bring much below normal temperatures behind the cold front with daytime highs as much as 20-25 degrees below normal across much of the interior West well into next week. This would support lowering snow levels in the mountains with potential for decent snow accumulations in the higher terrain of the north-central Rockies and in an emerging deformation area with the closed low. Ample upper trough/low energies slated to shift from the West/Rockies into the Plains next midweek would foster cyclogenesis/frontogenesis and emerging convective rainfall fueled by building moisture/instability. 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