Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1250 AM EDT Sat Jul 14 2018 Valid 12Z Tue Jul 17 2018 - 12Z Sat Jul 21 2018 ...Overview... The flow pattern across the contiguous U.S. will become a bit more amplified during the medium range period with an upper-level ridge expanding from the Great Basin to the southern Rockies, and a series of upper waves gradually carving out a trough across the Great Lakes. Heights are also expected to fall across the Pacific Northwest by late next week as an upper low digs south from the Gulf of Alaska toward the region. ...Guidance Evaluation and Preferences... A majority deterministic blend including the ECMWF/GFS/CMC was initially preferred during days 3-5 (Tue-Thu). Models have settled toward a somewhat slower/more amplified solution with the trough/upper low passing south of Hudson Bay and moving east into Quebec during this time frame. The same generally holds true for additional shortwave energy crossing the north central U.S. Wed-Thu, which then looks likely to amplify further across the Great Lakes/Ohio Valley Fri-Sat. Farther west, models continue to show a compact but energetic shortwave diving southeast across the Gulf of Alaska toward British Columbia Tue-Wed, with heights falling across the U.S. Pacific Northwest by later in the week. Some timing differences remain, but in general guidance has trended toward somewhat slower/more amplified solutions here as well. Given the increase in spread, majority weighting was shifted to ensemble means for days 6-7 (Fri-Sat), including the ECENS and NAEFS means. ...Weather Highlights/Threats... Showers and storms with locally heavy rain will accompany a cold front from the Appalachians to the Southeast/Mid-Atlantic/Northeast Tue-Wed. The trailing end of the frontal boundary is expected to stall from the Southeast to the southern/central plains, which could also focus locally heavy showers and thunderstorms through later next week. Monsoonal moisture will also produce scattered afternoon/evening thunderstorms from the southern Great Basin/Southwest to the southern/central Rockies through the next week, with locally heavy rain possible especially early in the week (the building upper-level ridge should gradually reduce the coverage of convection by later next week). In the wake of the cold front, high temperatures are expected to be 5 to 10 deg below average across the central/northern plains and portions of the Midwest/Great Lakes through much of next week. Hot temperatures across the Pacific Northwest (highs 5 to 10 deg above average) should moderate some by later next week as a Pacific cold front moves inland. Ryan WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found at: http://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif http://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif http://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html http://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml http://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 http://www.wpc.ncep.noaa.gov/heat_index.shtml