Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1153 AM EDT Wed Aug 22 2018 Valid 12Z Sat Aug 25 2018 - 12Z Wed Aug 29 2018 ...Due to technical difficulties, some WPC products may not be available or updated. We apologize for any inconvenience this may have caused... ...Pattern Overview and Guidance Evaluation/Preferences... Models continue to favor development of strong upper ridging across the north central/northeast Pacific, which favors downstream troughing across the western U.S. and expansion of upper ridging eastward from the lower/mid-Mississippi Valley to the Eastern Seaboard. Due to limited model availability, a blend of the 12Z guidance was used to generate medium range forecast products. The ECMWF and CMC solutions were favored over the 12Z GFS given their slower/more amplified solutions with upper trough/shortwave energy across the western U.S. throughout the period. ...Weather Highlights and Hazards... A weakening stationary frontal boundary along the Southeast U.S. coast through much of the medium range period will result in scattered to numerous showers and thunderstorms with locally heavy rainfall possible. Areas of potentially heavy convection will also be possible from the northern plains to the Great Lakes and New England a couple waves of low pressure traverse a frontal boundary. Scattered afternoon/evening showers and storms are also expected to persist across the Four Corners region, with monsoonal moisture remaining in place. Showers will spread into much of the Pacific Northwest as well as upper troughing amplifies overhead. As the upper ridge expands overhead, a warming trend will follow as high temperatures 5 to 10 deg F above average are forecast to expand eastward from the central U.S. toward the eastern U.S. during the weekend. Height falls across the Northwest will lead to a cooling trend with temperatures falling to more than 10 deg below average in the interior by Sunday into Monday. Ryan WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found 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