Extended Forecast Discussion NWS Weather Prediction Center College Park MD 429 PM EDT Tue Jun 16 2020 Valid 12Z Fri Jun 19 2020 - 12Z Tue Jun 23 2020 ...Overview and Weather/Hazard Highlights... A slow moving upper-level low centered over the central Appalachians Fri is forecast to gradually weaken as it moves eastward through the weekend, eventually becoming absorbed in stronger westerlies ahead of an amplifying northern stream trough. Showers and thunderstorms across the Appalachians and Mid-Atlantic Fri associated with this system should gradually diminish in coverage over the weekend. Upstream, another upper low in the northern stream is forecast to move east relatively slowly across the Canadian plains Fri through the weekend, with associated height falls and cold front crossing the U.S. Northern Plains and Upper Midwest. Ahead of this trough/cold front, high temperatures are forecast to be 5 to 15 deg F above average from the Great Lakes to the Northeast Fri and into the weekend. The trailing end of this frontal boundary is expected to stall across the Central/Southern Plains Fri-Sat, and linger through early next week with some reinforcement, as the main low pressure system moves into eastern Ontario and Quebec. The front will focus showers and thunderstorms Fri-Sat from the Plains to the Midwest, with locally heavy rains possible. By Sun-Tue as the trough/upper low moves farther east, shower and thunderstorm activity should shift farther south and east, from the Southern Plains and Lower Mississippi Valley to the Ohio Valley then the Appalachians. The Southern Plains may offer the most local heavy rain threat under an upper weakness. Out west, upper-level ridging should gradually strengthen over the Southwest this weekend and early next week, but Pacific shortwave energy and associated cold fronts will still affect the Northwest, with one system moving inland Sun-Mon, and another one off the coast by Tue. Given that the Sun-Mon system will be heading into broad anticyclonic flow, and will be weakening as it moves ashore, precipitation impacts across the Northwest will be relatively minimal, with only light precipitation expected. Additionally, as heights rise across the West next week, warming temperatures are also expected, with highs forecast to be 5 to 15 deg above average Sun-Tue across much of the Great Basin. ...Guidance/Predictability Assessment... A 00 UTC ECMWF/ECMWF ensemble mean blend was primarily used for the WPC medium range product suite along with the 13 UTC National Blend of Models. This composite seems to mesh best with overnight WPC short and medium range grid/qpf continuity and mitigates lingering differences with how quickly the eastern upper low lifts out and with the timing of the northern stream upper low crossing Canada. Schichtel/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 Hazards: - Heavy rain across portions of the Southern Plains, Mon, Jun 22. - Heavy rain across portions of the Central Plains, Fri, Jun 19. - Flooding possible across portions of the Northern Plains and the Northern Rockies. - Flooding occurring or imminent across portions of the Southeast, the Middle/Lower Mississippi Valley, and the Northern Plains. - Much above normal temperatures across portions of California, the Central Great Basin, the Pacific Northwest, and the Northern Great Basin, Sun-Mon, Jun 21-Jun 22. - Much above normal temperatures across portions of the Great Lakes and the Upper Mississippi Valley, Fri-Sat, Jun 19-Jun 20. - Much above normal temperatures across portions of the Northeast and the Great Lakes, Fri-Sun, Jun 19-Jun 21. 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