Extended Forecast Discussion NWS Weather Prediction Center College Park MD 249 AM EDT Wed Aug 14 2019 Valid 12Z Sat Aug 17 2019 - 12Z Wed Aug 21 2019 ...Overview and Guidance/Predictability Assessment... Models and ensembles agree at larger scales that upper ridging will build again into the Southwest near the New Mexico/Texas border by early next week as troughing digs down into the Northeast Pacific offshore British Columbia. Broad cyclonic flow will persist over southeastern Canada and through the Great Lakes/Northeast. The models and ensembles have converged toward a similar idea of the high-latitude flow out of Alaska/NW Canada that determines the shape/strength of the Northeast Pacific troughing. Flow depiction in this region has been particularly uncertain and run-run inconsistent in recent guidance. A composite blend of the latest runs of the GFS/ECMWF and increasingly their ensemble means over time seems to offer a good forecast starting point amid lingering uncertainty in system details. This features a stationary Southeast boundary, fronts moving through Canada and the U.S. northern tier, and western Canada to Northwest U.S. mean troughing. ...Weather Highlights/Threats... Heavy rain potential will persist this weekend into next week from the lower Mississippi Valley eastward in the vicinity of the Southeast U.S. stalled front, spreading modestly inland to the Tennessee Valley/Mid-South later period with return flow. To the north, shortwave passages along lead fronts will focus weeked convection from the Upper Midwest/Great Lakes eastward to the Ohio Valley and Northeast/Mid-Atlantic early-mid next week. In this pattern, temperatures will be above normal in the Southwest/Southern Plains for much of the period and some daily records will be possible with upper ridge expansion. Schichtel Additional 3-7 Day Hazards information can be found on the WPC medium range hazards 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