Extended Forecast Discussion NWS Weather Prediction Center College Park MD 249 AM EDT Wed Sep 25 2024 Valid 12Z Sat Sep 28 2024 - 12Z Wed Oct 02 2024 ...Pattern Overview and Guidance/Predictability Assessment... Models and ensembles have come into better overall agreement from the weekend into early next week. This generally includes the latest guidance from the 00 UTC cycle. A blocky split flow pattern develops across much of the country as highlighted aloft by a warming Rockies/Southwest ridge and a low/trough lifting over the Canadian Maritimes that sandwich a cutoff low settling over the Mid-South. Post Tropical Cyclone Helene will weaken into the weekend over the Mid-South entrained into the cutoff low, but remains a slow translation rainfall/runoff threat there and with trailing back moisture into the south- central Appalachians. Meanwhile, forecast spread is less then stellar over time with more progressive and energetic flow overtop from the northeast Pacific through the Northwest and downstream. Guidance varies with extent of potential southeastward digging of upper trough energy, modest to moderate rain focusing wavy frontal surges and post- frontal drying/cooling through the north-central/Midwest and eastern U.S. into next week, replacing/kicking the leading Mid- South cutoff low and lingering tropical moisture signature. Overall, a composite of compatible guidance of the GEFS/ECMWF/Canadian ensemble means, the National Blend of Models and WPC continuity seems to offer a good compromise forecast, albeit will smoothed detail through medium range time scales. ...Weather/Hazards Highlights... The WPC Day 4/Saturday and Day 5/Sunday Excessive Rainfall Outlooks show lingering and elongated Marginal Risk threat areas from the Mid-South with pooled tropical moisture around the post-tropical remains of Helene and with a trailing/lingering deepened moisture back through the south-central Appalachians and onward with a trailing wavy and slow moving front down over central Florida. More certain local focus closer to occurrence may lead to Slight Risk issuance upgrades given Helene moisture, especially given earlier period heavy rainfall will create saturated soils. 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 forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw