Extended Forecast Discussion NWS Weather Prediction Center College Park MD 333 PM EDT Fri Aug 02 2019 Valid 12Z Mon Aug 05 2019 - 12Z Fri Aug 09 2019 ...Overview and Guidance/Predictability Assessment... Upper ridging migrating slowly westward from the Gulf of Alaska to the Bering Sea through the forecast period favors troughing in the vicinity of the Pacific Northwest and downstream across the Great Lakes. Meanwhile upper ridging across the Four Corners region should gradually weaken. Models/ensembles showed good agreement at the larger scales through the medium range, but did show some variability with respect to the details of specific systems, but less than usual considering the amplified pattern. Given the general large scale agreement, a blend of the 00Z ECMWF/CMC/UKMET/06Z GFS was used as a forecast starting point with a slowly increasing percentage of ensemble mean (ECENS and NAEFS) weighting during days 5-7 (Wed-Fri). Considering the agreement, kept the weighting under 50% for the pressures, fronts, winds, and 500 hPa graphics. The remainder of the grids were weighted towards the 12z National Blend of Models. ...Weather Highlights/Threats... Monsoonal moisture will focus scattered showers and storms with locally heavy rainfall over the Four Corners next week as the upper high weakens. Elsewhere, rainfall will follow the front in the north but be more scattered and diurnally driven in the Southeast. Areas of more organized convection and heavy rain are possible across the central U.S. along the cold front. The Pacific Northwest will initially see high temperatures several degrees warmer than average Mon-Wed before a cooling trend arrives later in the week as the upper low begins to move inland. Relatively cool temperatures are also expected to move into the north central U.S. by Wed-Fri in the wake of the surface cold fronts, with high temperatures expected to be 5-10 deg F below average. Roth/Ryan 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 Hazards: - Heavy rain across portions of the Central/Southern Plains, the Middle/Lower Mississippi Valley, the Tennessee Valley, and the Ohio Valley, Mon-Fri, Aug 5-Aug 9. - Flooding possible across portions of the Central Plains and the Middle Mississippi Valley. - Flooding occurring or imminent across portions of the Central Plains, the Lower Mississippi Valley, and the Northern Plains. - Flooding likely across portions of the Central Plains, the Middle Mississippi Valley, and the Southern Plains. - Heavy rain across portions of mainland Alaska, Mon-Tue, Aug 5-Aug 6. - High winds across portions of mainland Alaska, Mon-Tue, Aug 5-Aug 6. 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