Extended Forecast Discussion NWS Weather Prediction Center College Park MD 315 AM 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 reasonably well clustered but smoothed guidance from the GEFS/ECMWF ensemble means, the NBM and with infusion with the latest implications from NHC tropical tracks for Nora and Ida. Individual models are beginning to offer some more common trends into medium range time scales, but still differ enough from run to run to favor the more ensemble mean forecast approach that offers better continuity in a pattern with near normal predictability. ...Pattern Overview with Weather/Hazard Highlights... By Thursday and into Friday, Ida as a still well organized post/extra tropical cyclone is forecast by the NHC to lift from the Mid-Atlantic to offshore southern New England with uncertain interaction from northern stream energies. This track would bring a heavy rainfall threat fueled by deep wrapping moisture in a favorable right entrance region of a potent upper jet. Cell training and terrain will significantly enhance the runoff/flood threat within a well defined precipitation axis. The latest track guidance for Nora brings it northward along the western Mexico coast and into Northwest Mexico where it will weaken rather quickly as it interacts with the terrain. Leading deep tropical moisture ahead of Nora will fuel a lingering Southwest U.S./Rockies heavy rain threat into Thursday. 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. 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