Extended Forecast Discussion NWS Weather Prediction Center College Park MD 114 AM EDT Fri Aug 21 2020 Valid 12Z Mon Aug 24 2020 - 12Z Fri Aug 28 2020 ...Hot conditions expected for the Southwest and portions of the central U.S. next week... ...Two tropical systems forecast to potentially affect the southern/southeastern U.S. next week... ...Overview and Weather/Hazard Highlights... A broad upper-level ridge is expected to persist across the CONUS southern tier during the extended forecast period, while an active jet traverses Canada and the northern tier. Two relatively persistent positive 500 hPa height anomaly centers are evident in ensemble means next week, one across the southwestern states, and another across the western Atlantic Ocean, between Bermuda and the Bahamas. The National Hurricane Center is currently issuing advisories on two tropical systems potentially affecting the U.S. next week. Tropical Depression Thirteen, currently east of the Leeward Islands, is forecast to strengthen to a tropical storm and pass across or near South Florida or the Keys on Monday, then turn northwest across the eastern Gulf of Mexico as a hurricane through early next week. Tropical Depression Fourteen, currently across the northwestern Caribbean Sea, is forecast to cross the Yucatan Peninsula this weekend before moving northwest across the central/western Gulf of Mexico as a hurricane early next week, eventually approach the western Gulf Coast states. Refer to advisories issued by the National Hurricane Center for the latest information on these systems. The combination of these two systems is expected to bring the potential for heavy rains next week from Florida to Texas. Any other potential impacts from these systems will become more clear over the next few days as confidence in the forecast tracks increases. The aforementioned positive height anomalies will serve to help steer the tropical systems, with T.D. Fourteen heading into a weakness across the central U.S., ad T.D. Thirteen initially taking a more westerly course south of the West Atlantic ridge center. The western ridge will continue to support above average temperatures across much of the western U.S., also extending into the north central U.S. early next week. High temperatures across the Southwest are forecast to continue soaring well past the 100 degree mark. While temperatures will not be quite as hot as seen in recent days, a few isolated record highs will still be possible next week. Additionally, highs are forecast to be 5 to 15 deg F above average across much of the north central U.S. Mon-Wed, with a few areas potentially surpassing 100 degrees, and a couple record high temperatures possible. Scattered showers and storms will be possible across the central/northern Rockies in association with a lingering frontal boundary, with convective activity gradually migrating eastward toward the central/northern High Plains later in the week. Farther east, the Great Lakes and Northeast may become convectively active by Thu as a shortwave and frontal system cross the region. ...Guidance/Predictability Assessment... A blend of the 12Z ECMWF/18Z GFS served as a basis for the WPC forecast initially during days 3-4 (Mon-Tue). After that, emphasis on ECENS/GEFS ensemble means was gradually boosted over time through days 5-7 (Wed-Fri). Forecast confidence was near to slightly above average early in the extended forecast period, given good large scale agreement and relatively good agreement on the details of specific features. From day 5 onward, confidence was average to slightly below average, with the biggest points of contention being timing/amplitude differences among the guidance with smaller-scale features in the active westerlies across Canada and the CONUS northern tier. Large-scale consensus, particularly among ensemble means, remained relatively good through day 7, however. 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