Extended Forecast Discussion NWS Weather Prediction Center College Park MD 155 PM EDT Mon Aug 24 2020 Valid 12Z Thu Aug 27 2020 - 12Z Mon Aug 31 2020 ...Heavy rain from Laura is expected to spread farther inland from the lower Mississippi Valley across the lower Ohio Valley and possibly into the Mid-Atlantic through Saturday... ...Overview and Guidance/Predictability Assessment... A pattern change is on tap with a more zonal flow across the northern tier of the CONUS by Thursday with what looks to be the last Gulf of Alaska low in this pattern ejecting into western Canada Friday with ridging building into the Alaska Panhandle/Yukon through this weekend. This encourages troughing into the Northwest CONUS, ridging over the Midwest/Great Lakes, and troughing over the Northeast. This pattern is well agreed upon among deterministic guidance through Day 5 and the 00Z ECENS/06Z GEFS. The track of Laura is of particular concern for the CONUS Days 4-6. There is good agreement with the track of Laura through Day 5 among global guidance with timing differences noted. The 00Z ECMWF/12Z CMC are the fastest while the GFS has been slowest. In fact the 12Z GFS is even a bit slower than the 06Z GFS. The 12Z UKMET is in between the faster and slower guidance. The 15Z NHC track is pretty close in timing to the 06Z GFS for Days 4/5. The 00Z UKMET was very slow with Laura and was not included in the model preference (which favors 00Z ECMWF/06Z GFS/00Z CMC for Days 3-5). ...Weather/Hazard Highlights... As Laura moves farther inland Thursday night, turning east over the southern OH/northern TN Valley Friday and gradually weakening, the system is expected to spread heavy rainfall, with potential flooding impacts, across portions of the lower Mississippi Valley and Tennessee/Ohio Valleys, as well as portions of the central Appalachians and Mid-Atlantic Friday night into Saturday. Potential interaction of the system with the shortwave crossing the Great Lakes and associated cold front could lead to areas of enhanced heavy rainfall threat near the track. Elsewhere, by Sat-Sun, a trailing stationary/warm front across the central U.S., and the approaching western U.S. upper trough, will focus areas of showers and thunderstorms across portions of the Central Plains and Mid-Mississippi Valley, eventually developing farther north across the Northern Plains/Upper Midwest as the stronger height falls associated with the trough spread east. Hot conditions will continue from the Southwest through Friday with max temperatures expected to finally drop below a positive 5 degree anomaly by Saturday. However, near/just above normal is still hot there this time of year. Much above normal temperatures persist through Friday for much of the central U.S. before shifting south to the Southern Plains and The east through the weekend. A few record high temperatures are possible for the southern Rockies and southern High Plains Fri/Sat, with temperatures surpassing 100 deg F across portions of West Texas. The trough expected to dig into the western U.S. Sun-Mon is forecast to bring much cooler temperatures to areas from the northern Great Basin to the northern Rockies, where highs Sun-Mon are expected to be 10-20 deg F below average. Morning low temperatures could drop to near or below freezing across the northern Rockies by Mon morning. 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