Extended Forecast Discussion NWS Weather Prediction Center College Park MD 124 AM EDT Wed Jul 03 2019 Valid 12Z Sat Jul 06 2019 - 12Z Wed Jul 10 2019 ...Overview and Guidance/Predictability Assessment... Typical summer pattern expected across the CONUS during the medium range. Downstream of a Rex block across the North Pacific, moderately progressive flow will pass between a building upper ridge across the CONUS southern tier, and a mean upper trough in the vicinity of Hudson Bay. An upper trough skirting the Great Lakes/Northeast Sat-Sun is expected to push a cold front southward through the central U.S. and eastward across the Ohio Valley to the Eastern Seaboard. The trailing end of this frontal boundary is expected to stall from the Southern Plains to the Southeast, lingering into early next week before it begins to lift back northward as a warm front ahead of the next system. Meanwhile, shortwave energy diving south on the eastern periphery of the Alaska ridge is expected to reach the Pacific northwest by the weekend, moving east across the northern Rockies by the early to middle portion of next week as it weakens. A multi-model blend including the ECMWF/GFS/UKMET/CMC was used as a forecast starting point during days 3-5 (Sat-Mon). These solutions handled the shortwave and cold front crossing the central/eastern U.S. during that time frame similarly. Models begin to show some differences surrounding the western trough starting on day 5, which grow substantially through the day 6-7 (Tue-Wed) time period. In general, models/ensembles have trended toward a slower eastward progression of this system, keeping lower heights in place across the western U.S. for longer. The GFS has consistently moved this energy eastward much quicker than consensus for the past several runs (an idea that is not supported by the GEFS mean), whereas the ECMWF has slowed the system down in line with the general trend and the ECENS/GEFS means. Thus, the forecast during days 6-7 was based on a blend of majority ECENS/GEFS ensemble means along with some continued use of the deterministic ECMWF (about 1/3) through the end of the forecast period. ...Weather Highlights/Threats... The frontal boundary crossing the central/eastern U.S. through much of the forecast period will focus areas of scattered to numerous showers and thunderstorms across a large area, including portions of the Plains, Ohio/Tennessee Valleys, and the Eastern Seaboard through the middle of next week. Models show a signal for areas of heavy rainfall along the immediate Southeast U.S. coastline from Sun into the middle of next week. A renewed threat of more widespread convection may develop across the Northern Plains and Upper Midwest by Mon-Tue as the next surface front and surface low move into the region ahead of the shortwave energy crossing the northern Rockies. High temperatures are expected to be 5 to 10 deg F above average across the Northeast on Sat ahead of the incoming cold front, but temperatures should decrease in the wake of the front to near seasonal norms starting on Sun. Meanwhile, a brief period below average temperatures is possible across the northern High Plains behind the front on Sat, before a return closer to normal on Sun. Finally, an area of relatively coo. temperatures (highs 5 to 10 deg below average) may accompany the upper trough across the Northwest/Great Basin/northern Rockies during the early to middle portion of next week. 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 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