Extended Forecast Discussion NWS Weather Prediction Center College Park MD 145 AM EDT Fri Jul 24 2020 Valid 12Z Mon Jul 27 2020 - 12Z Fri Jul 31 2020 ...Tropical Storm Hanna 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... A broad subtropical ridge is forecast to persist across the CONUS southern tier during the medium range period, while active westerly flow continues to traverse the northern tier. Model/ensemble guidance generally show the flow pattern becoming a bit more amplified through time, with a fairly significant upper trough possible across the Great Lakes/Northeast next week, a similar feature near or off the Pacific Northwest, and strong ridging in between. By the start of the medium range period/Monday, Tropical Storm Hanna should be weakening as a tropical depression over central Mexico. Though the most significant rainfall is forecast to be mostly in the short range period, heavy rainfall may linger into early next week across portions of south Texas and Mexico associated with Hanna. Refer to the latest from the National Hurricane Center on the forecast for Hanna. Elsewhere, instability along the Gulf Coast may bring a threat for heavy rainfall to central portions of the coast Monday/Tuesday next week. Farther north, a cold front is forecast to sweet southeastward across the Midwest/Ohio Valley, reaching the Eastern Seaboard by Wednesday. This front will be accompanied by scattered to numerous showers/storms and the potential for organized rainfall in spots. The trailing portion of this front is forecast to linger for several days across the Central U.S., where it will focus multiple rounds of showers and thunderstorms through the middle of next week from the Central Plains into the Midwest. Guidance continues to suggest monsoonal moisture from the Southwest U.S. may also enhance rainfall across portions of the Southern and Central Rockies. Over the Northwest, a building upper ridge favors temperatures of 5-15 deg F above normal Mon-Tue over parts of Washington and Oregon, returning back towards normal by mid week as Pacific troughing moves ashore. Meanwhile, another round of above normal temperatures is forecast from the Lower Great Lakes to the Mid-Atlantic/Northeast, ahead of a moderating cold front, with highs early next week 5-10+ deg F above normal. ...Guidance/Predictability Assessment... The guidance in the beginning of the period was relatively well clustered and so a mostly deterministic model blend (between the latest runs of the ECMWF, CMC, and GFS) worked well as a starting point. Timing differences, especially across the Eastern Pacific/Northwest coast began to emerge mid to late next week and so usage of the ensemble means increased amid the growing forecast spread and uncertainty. This solution mitigates the less predictable smaller scale variances while still maintaining good WPC continuity. Santorelli 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