Extended Forecast Discussion NWS Weather Prediction Center College Park MD 428 PM EDT Fri Aug 09 2019 Valid 12Z Mon Aug 12 2019 - 12Z Fri Aug 16 2019 ...Overview and Guidance/Predictability Assessment... Generally quasi-zonal flow is expected to prevail early next week across the CONUS, with embedded shortwaves tracking through and some indication of troughing along the West Coast. This trough is least amplified in the EC solutions. By midweek, more amplified flow begins rebuilding as a deeper trough pushes into the Northwest and ridging centered in the Southern Plains is expected to strengthen by Thu/Fri. This would likely lead to troughing downstream in the eastern U.S. Model guidance, particularly the GEFS and EC means, are in pretty good alignment with the pattern, so a multi-model blend was able to be used early on. The 00Z CMC by day 5/Wed pushes more energy into the eastern U.S. trough, deepening it more than other guidance into day 6/7. On the other hand, the GFS deterministic runs, particularly the 06Z run, flatten out that trough. Thus, the ECMWF and GEFS means made up the bulk of the forecast later in the period. Overall not many changes were needed to the overnight fronts/pressures forecast. ...Weather Highlights/Threats... Widespread rain and thunderstorms are expected around a low pressure system from the Northern Plains into the Upper Midwest and Ohio Valley early in the workweek ahead of a shortwave. Gulf moisture flowing into the vicinity of that front as it pushes into the Southeast will lead to scattered showers and thunderstorms there. Temperature-wise, above average temperatures are forecast in the southern tier underneath the upper high, leading to the likelihood of excessive heat and widespread record high minimum temperatures. Meanwhile the northwestern and north-central CONUS will generally have below average high temperatures. Tate 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 Middle Mississippi Valley, the Great Lakes, the Upper Mississippi Valley, and the Northern Plains, Mon, Aug 12. - Heavy rain across portions of the Southeast, Thu, Aug 15. - Heavy rain across portions of the Great Lakes, the Central Appalachians, and the Ohio Valley, Tue, Aug 13. - Flooding occurring or imminent across portions of the Central Plains, the Southern Plains, and the Northern Plains. - Flooding likely across portions of the Central Plains, the Middle Mississippi Valley, and the Northern Plains. - Excessive heat across portions of the Lower/Middle Mississippi Valley, the Tennessee/Ohio Valley, the Southeast, and the Southern Plains, Mon-Wed, Aug 12-Aug 14. - Excessive heat across portions of Southern Texas, Mon-Fri, Aug 12-Aug 16. - Excessive heat across portions of the Central Plains and the Middle Mississippi Valley, Mon, Aug 12. 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