Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1106 AM EDT Tue Aug 06 2019 Valid 12Z Fri Aug 09 2019 - 12Z Tue Aug 13 2019 ...Overview and Guidance/Predictability Assessment... The models and ensembles are showing the anomalous closed low off the Pacific northwest on day 3 to progress onshore and inland, deamplifying as it crosses the northern Plains. Downstream from the wave, the low level ridge builds into the Great Lakes and Ohio Valley, with the east coast trough deamplifying and then moving out to sea. By day 7, the pattern is quasi-zonal across the country. The primary anomalies are associated with a well defined southern Plains ridge, and a ridge building across the southwest Atlantic towards FL. An additional shortwave appears likely to approach the Pacific Northwest early next week, although models differ quite a bit by that time on the flow pattern across western/central Canada and the northwestern U.S. The manual progs used a consensus of the 06z GFS/06z GEFS Mean, along with the 00z ECMWF and ECMWF Ensemble Mean. This approach mitigates the model to model and run to run differences in the northwest US on day 7. The 06z GFS deamplified the wave pattern across the Pacific northwest, northern Rockies, northern Plains, and upper MS Valley. The 06z GFS matches teleconnections from a closed high over the eastern Pacific for August, so this run was used in lieu of the 00z run. ...Weather Highlights/Threats... The system coming into the northwest this weekend leads to a period of showers and thunderstorms over the northern Rockies and high Plains of MT. As the parent wave moves east, showers and storms develop then in the northern Plains and in the downstream warm advection pattern in the mid to upper MS Valley early next week. South of the trailing end of the frontal boundary across the southeast, showers and storms continue across the eastern Gulf coast and FL. Monsoonal moisture will keep diurnal showers and thunderstorms active across the Four Corners region and the southern/central Rockies through the forecast period, with a daily threat for locally heavy rainfall. The upper ridge will keep hot conditions in place for the Southern Plains, with high temperatures forecast to be 5 to 10 deg F above average through early next week. Cooler temperatures will accompany the Pacific shortwave inland, with highs forecast to be 5 to 15 deg below average from the Pacific Northwest to the northern Rockies Sat-Sun, spreading into the Northern Plains Mon-Tue. Petersen 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