Extended Forecast Discussion NWS Weather Prediction Center College Park MD 146 PM EDT Wed Sep 01 2021 Valid 12Z Sat Sep 04 2021 - 12Z Wed Sep 08 2021 ...Guidance Evaluation and Preferences... During the medium range period, the upper level pattern is forecast to evolve toward upper troughing over the Great Lakes region and East Coast while ridging builds over the Southwest U.S. into the Northern Rockies. As a result, periodic shortwave troughs and associated fronts moving through the flow will parade through the central and eastern U.S.. Finally, by day 6 and day 7, a shortwave trough will approach the Pacific Northwest. Overall, the model guidance is average to above average agreement and consistency from previous cycles and this leads to some higher forecast confidence. The main issues are tied with the amplification of troughing over the Great Lakes as well as the progression of shortwave energy dropping into the Pacific Northwest where the 06Z GFS was on the faster side of the model spread. Given the relatively good agreement, the WPC blend incorporated the 00Z ECMWF/UKMET/CMC and 06Z GFS near equally for days 3-5 then higher weights of the ECENS/GEFS means for days 6-7. ...Pattern Overview with Weather/Hazard Highlights... A series of energetic northern stream upper troughs will force several wavy frontal systems into the Northwest and out though the north-central U.S. and increasingly southward into next week across the central and eastern U.S. with main upper trough reinforcement/amplification. Conditions seem best for some locally enhanced lead system convection from the Great Lakes to the Mid-South and central Plains Saturday, with more modest potential downstream more into the southern and eastern U.S. Sunday into Monday. The next trough to move into the north-central U.S. should bring another chance for organized rainfall across parts of the Midwest and Upper Great Lakes by next Monday into Tuesday, with scattered trailing frontal activity then again settling down over the southern and eastern states into next midweek in response to upper trough amplification. Schichtel/Taylor 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