Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 AM EDT Sat Sep 19 2020 Valid 12Z Tue Sep 22 2020 - 12Z Sat Sep 26 2020 ...Heavy rainfall threat for the northwest Gulf Coast next week from Beta... ...Hurricane Teddy will move through Atlantic Canada just east of Maine on Tue/Wed... ...Overview... Deep upper lows near the Gulf of Alaska and just off the Northeast will favor ridging over the Rockies and toward the Plains next week. In the Gulf, tropical storm Beta is forecast to become a hurricane and move along/near the Texas coast toward Louisiana at a slow pace, leading to the potential for heavy rain along the coast but with a large degree of uncertainty. In the western Atlantic, major hurricane Teddy will lift northward into Nova Scotia and merge with a non-tropical low, spreading some wrap-around rain and wind across Maine. In addition, Teddy will continue to churn up waves along the East Coast which could cause life-threatening surf and rip current conditions. ...Guidance/Predictability Assessment... The latest 12z/18z deterministic guidance offered a reasonable cluster to start the forecast period outside the UKMET in the Gulf) and a general model blend was used for Tue/Wed. Afterwards, there remains significant spread with respect to the timing/depth of troughing through the Lower Mississippi Valley out ahead of Beta which will influence its path. Preference was for a slow motion northeastward later next week in between the quicker solutions and slowest ones that linger the system in the Gulf, depicted by the 03Z NHC forecast and coordinated yesterday past day 5. Ensembles show good agreement off the West Coast with an incoming trough and attendant surface cold front. Blended solution trending toward a majority ensemble mean solution sufficed. In the Northeast, post-Teddy upper pattern will bring in another trough across the Great Lakes Thursday in quasi-zonal flow. ...Weather/Hazard Highlights... Tropical storm Beta will likely take a path near enough to the coast to spread some heavy rain around its circulation next week, slowly migrating northward/northeastward in time. Range of solutions remains large, from light accumulations along the coast to in excess of 10" over the multi-day period. Given the official track, leaned toward the higher end along the coast and over the open water but this will be refined several more times before it will become more specific. Over Maine, Teddy will bring some rain to Maine but heavier amounts will be over Canada. A cold front will bring several days of rainfall to western WA/OR, focused mostly around Wednesday as the front moves inland. Showers will continue behind the front eastward to northern Idaho. Temperatures will remain above to much above normal throughout the period across the north-central U.S. and back into the interior West (through Thu/Fri). Highest anomalies will lie over the Dakotas/Upper Midwest where 70s/80s will be common. Approaching cold front next weekend will start to cool temperatures over the Rockies. Cooler than normal temperatures in the Lower Mississippi Valley will be in response to abundant clouds and showers/rain around Beta. 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