Extended Forecast Discussion NWS Weather Prediction Center College Park MD 251 AM 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. Twin tropical systems may have some affect on the Gulf (TD Twenty-Two) and perhaps Maine (Hurricane Teddy) directly or indirectly. At the least, Teddy will churn up waves in the Atlantic for the next several days. ...Guidance/Predictability Assessment... Through the 12Z/18Z guidance cycle, latest deterministic models offered a reasonable cluster to start the forecast period, and a blend was used as a starting point. Trend has been toward a more amplified/deeper solution just offshore New England as has been advertised by the ECMWF guidance the past several runs. This involves Hurricane Teddy becoming encapsulated within the digging trough in a striking extratropical transition over at least the Canadian Maritimes/Nova Scotia. To the south, TD Twenty-Two is forecast to meander off the Texas coast and then perhaps drift northward/northeastward by the end of the week. Ensembles differ on timing of this evolution, tied to the strength/path of ridging to the north that initially holds it in place before troughing from the northwest tugs at it later in the week. Consensus of the ensembles was preferred (by WPC and NHC) until some more details can be ascertained. Rest of the CONUS will be fairly quiet with ridging stretched from the Southwest to the Plains. ...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. Over the Gulf, TD Twenty-Two may bring heavy rain to at least parts of the coast on its forecast track, even while remaining offshore. 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. 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 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