Extended Forecast Discussion NWS Weather Prediction Center College Park MD 257 AM EDT Fri Sep 6 2024 Valid 12Z Mon Sep 09 2024 - 12Z Fri Sep 13 2024 ...Overview... The beginning of next week will be featured with an upper level trough across the Northeast U.S. and a large Canadian surface high. This will result in a high quality airmass across much of the Eastern U.S. with a hint of fall in the air, but a moderation trend ensues going into the middle of the week. Out West, the persistent upper ridge and widespread anomalous warmth will likely abate by the end of the week as an upper trough builds in across the West Coast and then the Intermountain West. Heavy rain and thunderstorms will continue to make weather headlines for the western Gulf Coast as another resurgence of Gulf moisture moves inland across Texas by Tuesday, but not much in terms of heavy rainfall elsewhere across the nation given a paucity of deep moisture outside of the Gulf Coast states. ...Guidance/Predictability Assessment... The 00Z model guidance suite features good overall synoptic scale agreement across the nation as the work week begins Monday, even though there are some lingering timing differences with leading shortwave perturbations across southern Canada, and the CMC is slower to erode the Eastern U.S. trough. The models have trended stronger with the large scale trough/upper low that develops across the West Coast/Intermountain West compared to recent cycles. Towards the end of the week, the GFS lifts the upper low out quicker across Montana and is stronger with the downstream ridge across the Great Lakes region. For the WPC overnight forecast, a blend of the deterministic GFS/CMC/UKMET/ECMWF was used as a baseline for the first half of the period through early Wednesday, with a little more weighting to the ECMWF and CMC guidance. Ensemble means were added gradually to make up about 50% of the blend by Friday, which helped to smooth out increasing mesoscale differences. ...Weather/Hazards Highlights... Tropical moisture moving into the southwestern Gulf is expected to bring an increasing threat for heavy rain to the coastal areas of the Texas Gulf Coast, which is covered by a Marginal Risk on the new Day 4/Monday ERO. Some of the latest model guidance shows the potential for impactful rainfall totals that will need to be monitored going into the Day 5/Tuesday time period, and a Slight Risk of excessive rainfall is now planned from near Corpus Christi to Lake Charles. This region will likely have noteworthy rainfall leading up to this, and this will make conditions more susceptible to potential flooding concerns. Otherwise, much of the country should be relatively uneventful and dry, although shortwave energy pivoting around the western-central U.S. upper ridging may produce isolated to scattered rainfall with mostly light amounts. Generally light rainfall ahead of the next Western U.S. trough should begin to move into the region late Tuesday and beyond. Temperatures are expected to be unseasonably warm by September standards across much of the north-central U.S., with highs running about 5 to 15 degrees above average from the Front Range of the Rockies to the western Great Lakes for much of the week. The hot weather expected across much of the West Coast and Intermountain West during the short range period is expected to improve going into the middle of next week as the upper trough builds southward and heralds the arrival of a cold front, bringing temperatures of 5-15 degrees below normal for portions of the West Coast states and into Nevada. Slightly below average readings are also likely for the Gulf Coast region (but still humid) owing to increased cloud cover and rain. Hamrick 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