Extended Forecast Discussion NWS Weather Prediction Center College Park MD 115 AM EDT Thu Aug 27 2020 Valid 12Z Sun Aug 30 2020 - 12Z Thu Sep 03 2020 ...Heavy rain possible across portions of the Plains and Mississippi Valley Sunday through Tuesday... ...Overview and Guidance/Predictability Assessment... Laura (forecast to be post-tropical) is forecast to be off the Northeast U.S. coast Sun morning, quickly moving out away from the U.S. Please refer to the latest advisories issued by the National Hurricane Center for the latest information on Laura. The amplified flow pattern advertised by model/ensemble guidance in recent days should be already in motion by the start of the medium range, as a vigorous mid/upper-level trough digs into the north central U.S. Sun through early next week. The ECMWF continues to show a significant component of the energy separating from the stronger westerlies, with a cutoff low developing across the Great Basin Mon-Tue, which then slowly drifts eastward toward the central U.S. through midweek. A strong early fall-like cold front still appears likely to accompany the leading shortwave energy across the northern Rockies and into the north central U.S. Sun through early next week. After being the sole deterministic solution showing that scenario last night, the ECMWF was joined by the CMC, along with a continually increasing number of ensemble members. The GFS has continued to keep the trough more consolidated and progressive, racing it eastward faster than almost any other guidance, including most GEFS ensemble members. Given these multi-day trends in the guidance, opted to lean fairly heavily toward the ECMWF/CMC idea, and away from the GFS for this forecast cycle. The WPC medium range forecast was based on a blend of the 12Z ECMWF/CMC during days 3-4 (Sun-Mon). During days 5-7 (Tue-Thu), a gradual shift was shown toward heavier weight on the ECENS/NAEFS ensemble means (especially the ECENS). ...Weather/Hazard Highlights... The upper-level trough digging into the north central U.S. early next week will be accompanied by a strong early fall-like cold front. Ahead of the trough and front, relatively widespread showers and thunderstorms are expected from the Central/Northern Plains to the Mississippi Valley, with areas of heavy rain possible. Guidance continues to show a signal for more widespread heavy rains for portions of the Mid-Mississippi Valley and possibly portions of the Southern Plains Sun-Tue, with enhanced frontal moisture feed and convergence along a lingering surface front. High temperatures 10 to 15 deg F below average are expected across the northern Rockies Sun, and into the north central U.S. Mon-Tue. Favored northern Rockies spots may have their first freezing temperatures in some time Mon-Tue mornings. Highs in the 60s and 70s will be common across the Central/Northern Plains and Upper Midwest Mon-Tue. Additionally, the upper-level low expected to develop across the Great Basin early next week should bring some level of enhanced moisture feed into the Four Corners region, at least temporarily enhancing monsoonal convective activity with the potential for locally heavy rains. Meanwhile, the heat will remain in place farther south, with highs expected to be 5 to 10 deg above average across much of Texas into next week, and many areas approaching or even surpassing 100 degrees. After just over a decade, this will be my last shift at the Weather Prediction Center. My journey will continue at the National Water Center in Tuscaloosa, Alabama. Ryan 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