Extended Forecast Discussion NWS Weather Prediction Center College Park MD 500 PM EDT Fri Sep 11 2020 Valid 12Z Mon Sep 14 2020 - 12Z Fri Sep 18 2020 ...Heavy rain threat increases along the central to eastern Gulf Coast next week as tropical depression 19 is forecast to intensify into a tropical storm and threaten the Gulf Coast... ...Some welcome rain should reach the Pacific Northwest early next week and linger into the end of the week... ...Guidance/Predictability Assessment... Model guidance this morning agrees quite well that a progressive northern stream will continue across the northern tier states while a large surface high pressure system will settle across the Great Lakes and then into much of the eastern U.S. through the medium-range period. Meanwhile, the National Hurricane Center has initiated advisories on tropical depression 19 (T.D. 19) located to the east of Miami, FL as of 5pm EDT. T.D. 19 is forecast to intensify into a tropical storm and reach the central Gulf Coast region during the middle of next week. Meanwhile off the coast of the Pacific Northwest, models continue show uncertainty regarding an upper-level low which is forecast to form and potentially linger into the latter part of next week. The ECMWF and EC mean show a slower progression of this feature toward the Pacific Northwest than the GFS/GEFS solutions. The GEFS, which is noticeably slower than the GFS, has been trending slower toward the EC/EC mean regarding this feature. In addition, references to climatology also support a wave that is situated slightly offshore. Therefore, the morning WPC medium range product suite was derived from a composite blend of the 06 UTC GFS/GEFS mean with the 00 UTC ECMWF/ECMWF ensemble mean, trending toward the ECMWF solutions for days 5-7 (Wed-Fri). ...Overview and Weather/Hazard Highlights... A complex evolution over the northeastern Pacific should yield a fairly deep trough/closed low that is slated to bring some welcome rainfall and cooler temperatures into the Northwest and northern California by early next week, lingering into late next week in a wet late summer pattern. A cool high pressure system forming under the progressive northern stream flow will bring cooler than normal temperatures across the Great Lakes and down much of the eastern U.S. early next week before moderating later in the week. Meanwhile, the threat of heavy rainfall will increase along the central to eastern Gulf Coast next week as T.S. 19 is forecast to reach the central Gulf Coast during the middle of the week. A lingering front will also help to focus rainfall along the eastern Gulf Coast into Florida as well as along the western Gulf Coast well into next week but the highest threat of heavy rain appears to be near and just east of where T.S. 19 makes landfall. Deep moisture and slow system translation suggest that heavy rainfall threat may work inland later next week over the MS/TN Valleys as per the aforementioned northern stream flow amplification and frontal interaction. Kong 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 Southeast, the Lower Mississippi Valley, the Southern Plains, and the Tennessee Valley, Wed-Fri, Sep 16-Sep 18. - Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Mon-Tue, Sep 14-Sep 15 and Thu-Fri, Sep 17-Sep 18. - Heavy rain across portions of the Southeast and the Lower Mississippi Valley, Mon-Fri, Sep 14-Sep 18. - Heavy rain across portions of the Southeast, Mon-Tue, Sep 14-Sep 15. - Much above normal temperatures across portions of the Central Plains and the Northern Plains, Mon-Tue, Sep 14-Sep 15. - Much above normal temperatures across portions of the Central Plains, the Upper Mississippi Valley, and the Northern Plains, Tue-Wed, Sep 15-Sep 16. - Heavy rain across portions of mainland Alaska and the Aleutians, Mon-Tue, Sep 14-Sep 15. - Heavy rain across portions of mainland Alaska, Tue-Wed, Sep 15-Sep 16. 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