Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1200 PM EDT Tue Sep 10 2019 Valid 12Z Fri Sep 13 2019 - 12Z Tue Sep 17 2019 ...Overview and Guidance Evaluation/Preferences... 15Z update... A couple of upper-level shortwaves are forecast to traverse the northern tier states from west to east during the medium range period before a more significant long wave trough settles into the Pacific Northwest early next week. Models indicate good agreement on the timings and amplitudes of the first couple of waves, with the 06Z GEFS mean noted to be slower than the rest of the guidance. The 06Z GFS and the 00Z EC mean agree very well with each other regarding these waves and they, along with some 00Z ECMWF, have used to generate the WPC wind and pressure fields through Day 5. For the long wave trough over the Pacific Northwest, the ECMWF solutions have shown very good run-to-run consistency while the GFS/GEFS solutions have come to a better agreement with the ECMWF in recent runs. Thus, more weights have been given to the ECMWF, particularly the 00Z EC mean for the WPC Day 6 and 7 grid fields. Farther south, an upper-level ridge is forecast to remain entrenched from the lower Mississippi Valley to the Southeast through much of the medium range. Meanwhile, models indicate an upper-level vortex will form underneath this upper ridge near the Southeast U.S. coast and drift southwestward into the eastern Gulf late this week. The ECMWF maintains the western-most track with this system, moving it toward the Texas coast. The GFS shows the eastern-most track, bringing a sheared system onshore into the eastern Gulf coast. The Canadian model is in between these solutions, bringing the system onshore into the central Gulf coast. Kong ...Weather Highlights/Threats... Scattered showers and thunderstorms will be possible from the Southern/Central Plains to the Upper Midwest, Ohio Valley, and Great Lakes Fri-Sat as the surface low pressure system moves from the north central U.S. into Canada, with the cold front trailing into the Mississippi/Ohio Valleys and the Southern Plains. Farther south, showers and thunderstorms are expected to become fairly widespread across the Gulf Coast states and the Southeast from late this week into early next week in association with an easterly wave propagating from the tropics across Florida and into the Gulf of Mexico. This system may produce localized areas of heavy rainfall. Meanwhile, the upper trough digging into the Northwest by Sun-Mon is expected to bring an increase in precipitation, especially to the mountain ranges of the Pacific Northwest and northern Rockies. Sufficient cold air may accompany this upper trough to bring the first round of snow to the higher peaks across the region. Finally, an increase in monsoonal moisture across the Southwest Sun-Mon is expected to bring scattered showers and thunderstorms to portions of the Four Corners region. High temperatures are forecast to be 5 to 15 deg F above average from the Ohio Valley to the Southeast and lower Mississippi Valley on Fri, with many areas reaching well into the 90s. Some slight moderation in temperatures is possible by the weekend, but highs are expected to remain 5 to 10 deg above average beneath the upper ridge. The upper trough reaching the western U.S. Sun-Mon will bring much cooler temperatures, with highs 5 to 15 deg below average expected to overspread the Northwest and northern Great Basin. Meanwhile, temperatures ahead of the trough will warm across the Plains and the Upper Midwest, where highs may reach 5 to 15 deg above average by early 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