Extended Forecast Discussion NWS Weather Prediction Center College Park MD 430 PM EDT Fri Sep 18 2020 Valid 12Z Mon Sep 21 2020 - 12Z Fri Sep 25 2020 ...Heavy rainfall threat for the Western and Northwest Gulf Coast next week from TD Twenty-Two... ...Hurricane Teddy may pose a threat to the Canadian Maritimes/parts of New England... ...Overview... Upper ridging will build into the Rockies and toward the Plains next week as troughing eases into the Pacific Northwest and eventually the East. Confidence is increasing on twin tropical systems having an affect on the Gulf (TD Twenty-Two) and perhaps Maine (Hurricane Teddy) directly or indirectly. At the very least, Teddy will churn up waves in the Atlantic into the medium range period before it races into Eastern Canada as an extra Tropical low. ...Guidance/Predictability Assessment... The latest 00z/06z deterministic guidance offered a reasonable cluster to start the forecast period, and so a general model blend was used for days 3-4. After this, the trend continues towards a more amplified/deeper solution offshore New England which should eventually encapsulate/absorb Hurricane Teddy around day 5 over the Canadian Maritimes/Nova Scotia. To the south, what is currently TD Twenty-Two is forecast to meander near/off the Texas coast (as a TS or Hurricane) and then perhaps drift slowly northward/northeastward by the end of the week. Especially after mid-week, there remains significant spread with respect to timing of this evolution (both with deterministic and ensembles), which is tied to strength/path of ridging to the north initially holding it in place before troughing from the northwest pulls it northward. The ECMWF is the fastest of the deterministic solutions with this scenario, while the CMC keeps the system out over the Gulf waters. The latest forecast from the NHC appears to prefer a consensus of the GFS/ECMWF deterministic solutions along with ensemble means. ...Weather/Hazard Highlights... Teddy will bring heavy rain and strong winds to at least Atlantic Canada but perhaps back to Maine depending on its track/interaction with the upper trough. High pressure initially over New England on Monday will bring in much cooler temperatures to the East with a slow moderation the rest of the week. Over the Gulf, models show good agreement that TD Twenty-Two should bring heavy rain and coastal flood concerns to at least parts of the western to northwestern Gulf coast, regardless of the current spread in eventual track. Over the Pacific Northwest, a cold front will bring in rainfall to western WA/OR later in the week. Elsewhere, temperatures will remain above to much above normal throughout the period across the north-central U.S. and back into the interior West. Highest anomalies will lie over the Dakotas/Upper Midwest where 70s/80s will be common. Santorelli/Fracasso 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 Pacific Northwest and the Northern Great Basin, Wed-Thu, Sep 23-Sep 24. - Heavy rain across portions of the Southeast, the Lower Mississippi Valley, and the Southern Plains, Mon-Fri, Sep 21-Sep 25. - Flooding possible across portions of the Southeast, the Mid-Atlantic, and the Southern Appalachians. - Flooding occurring or imminent across portions of the Southeast and the Southern Appalachians. - Flooding likely across portions of the Southeast and the Southern Appalachians. - Much above normal temperatures across portions of the Central Plains, the Upper Mississippi Valley, the Northern Plains, and the Northern Rockies, Thu-Fri, Sep 24-Sep 25. - Much above normal temperatures across portions of the Central Plains, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Northern Plains, Mon-Tue, Sep 21-Sep 22. - Much below normal temperatures across portions of the Northeast, the Central Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, the Great Lakes, and the Ohio Valley, Mon-Tue, Sep 21-Sep 22. - Much below normal temperatures across portions of the Mid-Atlantic, the Northeast, and the Great Lakes, Mon, Sep 21. - High significant wave heights for coastal portions of the Southern Plains, Mon-Thu, Sep 21-Sep 24. - Heavy precipitation across portions of the Alaska Panhandle and mainland Alaska, Mon-Tue, Sep 21-Sep 22. - Heavy precipitation across portions of the Alaska Panhandle, Tue-Wed, Sep 22-Sep 23. - High winds across portions of the Alaska Panhandle, Tue-Wed, Sep 22-Sep 23. 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