Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Sat Aug 06 2022 Valid 12Z Tue Aug 09 2022 - 12Z Sat Aug 13 2022 ...Potentially heavy rainfall and flash flooding are possible in the Ohio/Tennessee Valleys Tuesday-Wednesday while monsoonal moisture continues in the West... ...Overview... The overall weather pattern across the contiguous U.S. next week is forecast to amplify into a trough-ridge-trough pattern, as shortwaves combine to deepen a trough in the East, a slow-moving upper low off the West Coast lifts northeastward into the Pacific Northwest around Wednesday-Thursday, and an upper high nudges eastward from the central Rockies into the central/southern Plains. Moisture lifted ahead of the eastern trough and associated cold front will likely lead to areas of heavy rain and thunderstorms mainly across the Ohio and Tennessee Valleys Tuesday-Wednesday with scattered convection spreading into the Eastern Seaboard as well. Meanwhile, persistent monsoonal moisture looks to continue across portions of the West, leading to additional rainfall with a gradual northward expansion of the rain toward the northern Rockies as the week progresses. ...Guidance Evaluation/Predictability Assessment... Ensemble means from the GEFS, ECMWF, and CMC continue to show good agreement with one another with respect to the aforementioned synoptic scale evolution for next week. The largest model spread continues to be located from off the West Coast to the Pacific Northwest where an upper low is forecast to track through. Ensemble means have generally slowed down the low track slightly in the past few runs while the fast deterministic solutions from the ECMWF and GFS have slowed down considerably to better agree with their respective ensemble mean positions. On the other hand, the CMC's forecast positions of the upper low is slightly slower than its ensemble mean. Meanwhile, model spread remains modest with the evolution of the East Coast trough late next week. Near the Gulf Coast, the GFS was most enthusiastic with a tropical low bringing tropical moisture onshore toward the latter part of next week. The WPC medium-range forecast package was based on, 40% from the 00Z ECMWF/00Z mean, 40% from the 06Z GFS/GEFS, and 20% from the 00Z CMC/CMC mean, transitioning to mostly a consensus of the ensemble means by Day 7, and consensus with the NBM. The results show good continuity with the previous forecast package. ...Weather/Hazards Highlights... For the early part of the medium range period Tuesday-Wednesday, an axis of locally heavy rain and thunderstorms ahead of a cold front is expected to continue pushing southeastward across the Ohio Valley to Northeast into the Tennessee Valley and Mid-Atlantic region. The relatively slow push of the front could lead to training storms that could cause flash flooding. Flooding concerns are particularly enhanced across portions of Kentucky/Tennessee/West Virginia on Wednesday, as they have received abundant rainfall recently and are sensitive to additional rain amounts. The front continuing to push southeastward into the latter half of the week should clear rainfall out of the northeastern quadrant of the country, but scattered convective activity is forecast to continue in the Southeast. Meanwhile, monsoonal moisture continues to impact the Southwest with enhanced rainfall, with a trend toward gradually less rainfall in areas like New Mexico but increasing chances for rain farther north as the moisture plume expands into the Intermountain West and Great Basin, with some locally heavy totals possible here as well. Very warm to hot temperatures around 10-15F above average, though not quite to record-breaking levels, are forecast to shift from the Northwest Tuesday into the northern and then central Plains as the workweek progresses with the eastward nudge of the upper high. Farther east, slightly below normal highs are possible in the Ohio and Tennessee Valleys behind the cold front, while temperatures along the Eastern Seaboard will flip from slightly above to slightly below average. Given the rainfall and cloudiness over the Southwest and Great Basin, highs are likely to be several degrees below normal there through late week. Kong/Tate Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml