Extended Forecast Discussion NWS Weather Prediction Center College Park MD 301 PM EDT Mon Aug 30 2021 Valid 12Z Thu Sep 02 2021 - 12Z Mon Sep 06 2021 ...Ida Heavy Rainfall/Flooding Threat to spread from the Mid-Atlantic to Southern New England Thursday... ...Nora lead moisture to fuel Southwest U.S./Rockies Heavy Rain threat into Thursday... ...Emerging late week locally heavy convective rainfall pattern for the Northern Plains/Upper Midwest... ...Guidance Evaluation and Preferences... The WPC medium range product suite was primarily derived from a composite blend of the NBM along with emphasis with the CMC/ECWMF/EC ensembles as they handled the heavy rain areas associated with NHC tropical tracks for Nora and Ida fairly well. ...Pattern Overview with Weather/Hazard Highlights... Ida is still forecast to be a well organized post-tropical cyclone that will be lifting from the Mid-Atlantic to offshore southern New England early in the extended period. Uncertain interaction from northern stream energies may alter Ida's track as it pulls offshore the New England coast. Deep tropical moisture wrapping into the low, within the right entrance region of a potent upper jet, will spread moderate to heavy rainfall across parts of the Northeast. Cell training and terrain will significantly enhance the runoff/flood threat within a well defined precipitation axis. There may be an increased threat for flash flooding for this part of the country. Nora is expected to be history before the extended forecast begins, however the remnant moisture aloft will transport northward into Arizona, New Mexico and points to the north. Showers and thunderstorms will linger across the Southwest U.S./Rockies into Thursday before the airmass begins to dry. Elsewhere, ample northern stream upper troughing will meanwhile dig a wavy and modestly unsettling/cooling front through the West and downstream across the north-central states. Upper dynamics and frontal convergence/progression should act to focus some locally heavy convection/rainfall as enhanced by embedded impulses/frontal waves as fueled by instability and frontal moisture pooling, including some monsoonal influx Thursday and Friday. There may be enhanced rainfall that setups up over the Dakotas and parts of Minnesota and Iowa. Campbell 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