Extended Forecast Discussion NWS Weather Prediction Center College Park MD 154 PM EDT Wed Sep 16 2020 Valid 12Z Sat Sep 19 2020 - 12Z Wed Sep 23 2020 ...Heavy rainfall possible along parts of the western to west-central Gulf Coast associated with possible tropical development in the Southwest Gulf... ...Guidance/Predictability Assessment... For the first couple of days of the medium range period, the deterministic guidance is pretty well clustered across the CONUS. Thus, a blend of the latest GFS/ECMWF/CMC/UKMET sufficed for days 3 and 4. After this, there is some question on how much a shortwave moving through the Great Lakes amplifies across the Northeast, which has implications for the eventual track of Hurricane Teddy during the day 6-7 frame. The ECMWF has been consistent the past few runs with a slower Northeast U.S. trough which could help to steer Teddy (likely beginning extra tropical transition by that point) more towards the Canadian Maritimes during the middle of next week. The latest 12z GFS/CMC are faster to progress the shortwave across the Northeast which kicks Teddy out to sea. As expected, there is considerable spread in the guidance with this so leaning more towards the better compatible GEFS/ECENS means days 5-7 is the best approach at this point. This also allows good WPC continuity with last nights forecast. ...Overview and Weather/Hazard Highlights... In the wake of Sally, strong high pressure settling into the East will bring well below normal temperatures including a few record values this weekend into early next week, with gradual moderation from west to east. The high pressure surge will also act to confine deeper moisture mainly to Florida and the Gulf of Mexico near a slow moving trailing front to linger over the next week. NHC is monitoring a slow moving tropical disturbance over the southwest Gulf of Mexico and broad deep moisture seems set to fuel widespread moderate to heavy rainfall that may feed into the western to west-central Gulf Coast. Elsewhere, amplified upper trough/embedded low ejection will spread some welcome rainfall and cooler temperatures out from the fire stricken Northwest and northern California to the northern Intermountain West/Rockies this weekend. Ahead of this system, the warmest temperature anomalies in the 10-15F range will focus into the northern-central states. Santorelli/Schichtel 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