Extended Forecast Discussion NWS Weather Prediction Center College Park MD 241 PM EDT Thu Aug 8 2024 Valid 12Z Sun Aug 11 2024 - 12Z Thu Aug 15 2024 ...Excessive Heat lingers over portions of Texas and the central Gulf Coast into next week... ...Overview... Upper pattern over North America will feature strong ridging over central Canada moving slowly eastward into Hudson Bay, a closed upper high over Texas, and troughing along both the West and East Coasts. A frontal boundary will linger across the Southeast and back into the Plains where the focus for convection will lie. In addition, with a southeast flow in the mid-levels out of Mexico into the Southwest, monsoonal rains will continue through the period over the Four Corners region. ...Guidance/Predictability Assessment... The 00/06Z guidance suite offered reasonable clustering through the period, and a blend of the GFS/ECMWF and their ensembles were used for the starting point (along with some of the Canadian and UKMET to start). The 13Z NBM was used as a starting point for the sensible weather grids, with minor adjustments. ...Weather/Hazards Highlights... Monsoonal moisture flow on the western side of the ridge centered over Texas will keep a wet and unsettled pattern in place from the Four Corners region northward into the central Rockies/High Plains for Sunday/Monday. Marginal EROs are in place here for Days 4/5. With the surface high shifting east to the Midwest on Sunday, the clockwise flow opens the western Gulf to transport moisture up the Plains where some isolated heavy rain threat exists anywhere from the Rockies onto the Plains. A broad Marginal Risk covers much of the Plains due to uncertainty at this time range. By Day 5, continued the Marginal Risk over the central Plains given little change in the overall pattern and surface front. Convective processes are not handled well in global models and will likely cause further adjustment/refinement to these areas with possible upgrades in the coming days, so stay tuned. Finally, a persistent front over the Southeast/Carolinas looks to produce widespread rain with embedded heavier rain where recent excessive rainfall from Debby has resulted in fully saturated soils that may only partially recover by then. Marginal Risks are in effect in this part of the Southeast for Days 4/5. Above seasonal normal temperatures persist over Texas to the central Gulf coast into next week beneath and downstream of a ridge axis over west Texas. HeatRisk values will be at Moderate to Major levels with some isolated Extreme values. Below normal temperatures over the central U.S. persist behind a cold front into Monday before return flow brings temps back toward normal Tues- Thurs. Fracasso/Jackson 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