Extended Forecast Discussion NWS Weather Prediction Center College Park MD 114 AM EDT Thu Jul 23 2020 Valid 12Z Sun Jul 26 2020 - 12Z Thu Jul 30 2020 ...Tropical Depression Eight expected spread heavy rain across South Texas and portions of the Gulf Coast this weekend into early next week... ...Overview and Weather/Hazard Highlights... A broad subtropical ridge is forecast to persist across the CONUS southern tier during the medium range, while active westerly flow continues to traverse the northern tier. Model/ensemble guidance generally slow the flow pattern becoming a bit more amplified through time, with a fairly significant upper trough possible across the Great Lakes/Northeast next week, and a similar feature near or off the Pacific Northwest, and strong ridging in between. Newly-formed Tropical Depression Eight in the Gulf of Mexico is forecast by the National Hurricane Center to move west-northwestward, eventually making landfall as a tropical storm along the central Texas coast on Saturday. By the start of the medium range (Sunday), the system is forecast to be gradually weakening across inland South Texas as it continues to move westward. The system is forecast to produce heavy rains and possible flooding across South Texas over the weekend, where several inches of rain (2-5 inches, with localized 6+ inches) are forecast to fall. Farther north, a cold front is forecast to sweep southeastward across the Midwest and the Mississippi/Ohio Valleys Sun-Tue, reaching the Eastern Seaboard by Wed as a somewhat deeper surface low wraps up across southern Quebec. This system will be accompanied by scattered to numerous showers/storms. The trailing portion of the front is forecast to linger for several days across the Central Plains, where it will also focus multiple rounds of showers and thunderstorms Sun through the middle of next week. Additionally, monsoonal moisture will bring scattered showers and storms to the Four Corners region. This activity will be diurnal, but will have the potential to produce locally heavy rains. Another round of above normal temperatures is forecast from the Midwest to the Mid-Atlantic and Northeast, ahead of the cold front. Highs Sun-Mon are forecast to be 5 to 10 deg F above normal. As the cold front sweeps through, highs will return closer to seasonal norms, but hot conditions could persist across the Mid-Atlantic into Tue before the front passes through that region. ...Guidance/Predictability Assessment... A blend of the 12Z ECMWF/18Z GFS was used as a basis for the forecast during days 3-4 (Sun-Mon). After that, a gradual shift toward heavier weighting of ensemble means (ECENS and GEFS) was shown through time, with majority ensemble means by days 6-7 (Wed-Thu). Overall, models/ensembles showed relatively good consensus at the larger scales through the medium range. The most significant differences noted in the guidance pertained to the amplitude of troughing across the eastern U.S. by next Wed-Thu, and to what extent the ridge can build northward into the Pacific Northwest around the same time (shifting the trough farther off the West Coast). Ensemble means were in much closer agreement on these features than the deterministic guidance, and provided good forecast continuity, hence the shift toward the means during the latter portion of the extended forecast. 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