Extended Forecast Discussion NWS Weather Prediction Center College Park MD 311 PM EDT Thu Jul 23 2020 Valid 12Z Sun Jul 26 2020 - 12Z Thu Jul 30 2020 ...Tropical Depression Eight to gain strength over the Gulf of Mexico and offer a Gulf Coast to South Texas/Mexico heavy rain and runoff threat this weekend/early next week... ...Overview and Weather/Hazard Highlights... It remains the case that 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. Tropical Depression Eight is forecast by NHC to gain strength over the Gulf of Mexico prior to landfall 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/mid-lower Rio Grande Valley/Mexico over the weekend, lingering into early next week. Heavy tropical rains and runoff issues are expected with 2-5" to localized 6-10" storm total amounts forecast to fall over the region as fueled by tropical precipitable waters values that rise and linger above 2". 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. There is a decent guidance signal suggesting monsoonal moisture feed from the Southwest will enhanced rainfall potential through the period. 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... The WPC medium range product suite was mainly derived from a blend of reasonably well clustered medium to larger scale guidance from the 06 UTC GFS/GEFS mean, 00 UTC ECMWF/Canadian and ECMWF ensemble mean and the 13 UTC National Blend of Models. Applied most blend emphasis on the models Sun-Tue and then shifted weighting to the ensemble means next Wed/Thu amid growing forecast spread and uncertainty. This overall solution tends to mitigate less predictable smaller scale variance and maintains good WPC continuity. Schichtel/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