Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1252 PM EDT Fri Aug 21 2020 Valid 12Z Mon Aug 24 2020 - 12Z Fri Aug 28 2020 ...The heat wave continues in the Southwest through next week and portions of the northern U.S. through the middle of next week... ...Two tropical systems forecast to affect the southern/southeastern U.S. next week... ...Overview and Weather/Hazard Highlights... A broad upper-level ridge axis is expected to pivot over the Four Corners next week as troughing moving into western Canada shifts east across the Canadian Prairies through midweek. Two relatively persistent positive 500 hPa height anomaly centers are evident in ensemble means next week, this ridge 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 Storm Laura is nearing the Leeward Islands and is forecast to remain a tropical storm as it pushes west-northwest across the Great Antilles into Monday, then strengthen as it moves in to the Gulf of Mexico. Tropical Depression Fourteen, currently north of Honduras, is forecast to cross the Yucatan Peninsula this weekend before moving northwest across the central/western Gulf of Mexico with potential to be a hurricane early next week, eventually reaching the western Gulf Coast. Refer to advisories issued by the National Hurricane Center for the latest information on these systems. The combination of these two systems, and their associated tropical moisture brings the potential for heavy rains next week from Florida to Texas. Considerable uncertainty reigns with these systems, however. 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 south-central U.S., and Laura initially taking a more westerly course south of the West Atlantic ridge center before potentially turning north over the Gulf of Mexico. 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. Max 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 isolated record max temps will still be possible next week, particularly near the south-central Rockies. Additionally, max temps are forecast to be 5 to 15 deg F above average across much of the north-central U.S. Mon-Wed, with areas in the north-central Plains targeted to surpass 100 degrees, and a couple record max 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 00Z ECMWF/06Z GFS/00Z CMC served as a basis for the WPC forecast during days 3-4 (Mon-Tue). The 00Z CMC was included because of it's stronger development of Laura which is in line with the NHC forecast. After that, emphasis is on the 00Z ECMWF/ECENS and 06Z GFS/GEFS. 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 outside of tropical activity. There is considerable uncertainty with the tracks of Laura/14 and the 12Z GFS has come in with more westerly tracks for both systems, furthering the uncertainty. From day 5 onward, confidence remains 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. Jackson 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