Extended Forecast Discussion NWS Weather Prediction Center College Park MD 452 PM EDT Tue Jul 21 2020 Valid 12Z Fri Jul 24 2020 - 12Z Tue Jul 28 2020 ...West Gulf Coast to West-Central Texas Excessive Tropical Rainfall/Runoff Threat... ...Overview and Weather/Hazard Highlights... The National Hurricane Center is monitoring an area of convection over the Gulf of Mexico that offers potential for development later week into the weekend. An expected low track and deep moisture feed inland from the West Gulf Coast inland to west-central TX as the low dissipates offers a threat for local excessive rainfall and runoff issues. An upper-level ridge will intensify out from the lower/mid-Mississippi Valley to promote more hot temperatures over an expansive area of the nation. Highest anomalies may stretch from the North-central Plains/Upper Midwest to the Eastern Seaboard into early next week, with high temperatures forecast 5 to 10+ deg F above average. As is typical of such a pattern, the weather around the periphery will be active across a number of areas. Shortwave energy and associated surface frontal systems traversing mid/upper-level westerlies across the CONUS northern tier will result in the potential for showers and thunderstorms across several days from the Northern Plains/Upper Midwest east across the Great Lakes and the Northeast. The latest model guidance continues to show a signal for areas of heavy rain across the Northern Plains/Upper Midwest Fri-Sat and again on Sun-Mon. The southern Mid-Atlantic and portions of the Southeast will see scattered to numerous showers and storms Fri-Sat as a frontal boundary sags across those areas. Finally, the seasonal monsoon will be active across the Southwest/Four Corners regions late this week into the weekend, on the western side of the central U.S. ridge. Areas of heavy rain are possible and any tropical surge over TX toward the southern High Plains/Rockies by early next week only adds fueling moisture. ...Guidance/Predictability Assessment... Model guidance as relatively agreeable during the first half of the medium range, but consensus degraded later in the forecast period a bit more quickly than in recent days. A blend of the 00 UTC ECMWF/06 UTC GFS was heavily used during days 3-4 (Fri-Sat), with a fairly rapid shift toward ensemble means after that, and a mostly ensemble mean-based forecast by days 6-7 (Mon-Tue). Deterministic guidance seemed to be struggling by the early next week with both the timing and intensity of shortwaves traversing the active westerlies across Canada and the U.S. northern tier, with solutions nearly out of phase with each other in some instances. Ensemble means provided a bit more stability and consistency to the forecast by that time frame, and thus the emphasis placed on ensemble mean solutions by that time frame. Forecast confidence was average to slightly above average during days 3-4, and average to below average by days 6-7. Ryan/Schichtel Hazards: - Heavy rain across the central to western portions of the Gulf Coast into south-central Texas, near the North Carolina coast, over the Upper Mississippi Valley, as well as parts of the southern Rockies, Fri-Sat, Jul 24-Jul 25. - Heavy rain across portions of the northern Plains, as well as the eastern slopes of the central to southern Rockies and nearby High Plains, Sun-Mon, Jul 26-Jul 27. - Heavy rain across portions of the eastern slopes of the southern Rockies and nearby High Plains, Mon-Tue, Jul 27-Jul 28. - Heavy rain across northern Missouri, Tue, Jul 28. - Flooding possible across portions of the central Plains. - Flooding occurring or imminent across portions of the northern Plains. - Flooding likely across portions of the mid-Mississippi Valley. - Excessive heat across portions of the central Plains, the mid and upper Mississippi Valley, and the northern Plains, Sun, Jul 26. - Excessive heat across portions of the central and northern Plains, and the upper Mississippi Valley, Fri-Sat, Jul 24-Jul 25. - Excessive heat across portions of the mid-Mississippi Valley, Mon, Jul 27. - Excessive heat across portions of the lower Mississippi Valley, and the Mid-Atlantic, Mon-Tue, Jul 27-Jul 28. - Much above normal temperatures across portions of the northern Plains, the upper Mississippi Valley, and into the Great Lakes, Fri-Sun, Jul 24-Jul 26. - Much above normal temperatures across portions of the interior Mid-Atlantic into the central Appalachians, Mon-Tue, Jul 27-Jul 28. - Much above normal temperatures across portions of the central Great Lakes, Fri-Mon, Jul 24-Jul 27. 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