Extended Forecast Discussion NWS Weather Prediction Center College Park MD 249 AM EDT Sat Aug 28 2021 Valid 12Z Tue Aug 31 2021 - 12Z Sat Sep 04 2021 ...Major Hurricane Ida to bring a Heavy Rainfall/Flooding Threat from the central Gulf Coast to the Mid-Atlantic... ...Potent Nora track into Baja CA/Gulf of CA to fuel a lead Southwest U.S. Heavy Rain Threat mid-later next week... ...Guidance Evaluation and Preferences... The big story continues to be impending hazardous impacts from Hurricane Ida from the Gulf of Mexico and potent east tropical Pacific Nora, forecast to track northward up the Gulf of California. Please refer to products from the National Hurricane Center and the local offices to obtain the latest information regarding these dangerous systems. The WPC medium range product suite was primarily derived in conjunction with NHC tracks for Ida and Nora along with well clustered guidance from the 12/00 UTC ECMWF, ECMWF/GEFS ensembles and WPC continuity that seems to best fit NHC and the overall flow pattern over the rest of the lower 48 in a pattern with average to above average predictability. ...Pattern Overview with Weather/Hazard Highlights... Dangerous Hurricane Ida is expected to strengthen further over the Gulf of Mexico as it moves steadily towards the northwest with an expected landfall along the Louisiana coast late Sunday as a major hurricane. Ida will bring powerful and gusty winds and very heavy rainfall to the central Gulf Coast region. Gradually weakening but still very wet Ida is forecast to make a sharp turn to the east-northeast spreading the heavy rainfall threat into the Tennessee/Ohio Valleys into Tuesday/Wednesday. Considerable flash, urban, small stream, and riverine flooding is likely with Ida. Deep moisture feeding inland with time will also interact with a slow moving front draped over the system, offering a lead heavy rainfall focus into the central Appalachians and Mid-Atlantic into Wednesday/Thursday. Tropical Storm Nora is also forecast to become a Hurricane with the current track guidance from NHC bringing it northward into the Gulf of California and eventually into far northwest Mexico. Leading deep tropical moisture ahead of Nora will likely fuel a Southwest U.S. heavy rain threat next week. The guidance continues to show some uncertainty in the track and certainly a track for longer over the Gulf waters could bring a more substantial heavy rainfall threat into the Southwest. By later next week, leading moisture may also bring moderate to locally heavy, and terrain enhanced, rains into the central Rockies as well. Elsewhere, ample northern stream upper troughing will meanwhile dig a wavy but only modestly unsettling/cooling front down from the Northwest. Subsequent system progressions and genesis mid-later next week out across the Rockies to the north-central U.S. will increasingly focus an enhanced convection/rainfall pattern that could focus locally heavy convection/rainfall as enhanced by embedded impulses and frontal/wave reinforcements. Moisture/instability pooling may support some locally strong to severe convection and heavy downpours. Schichtel Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook 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