Extended Forecast Discussion NWS Weather Prediction Center College Park MD 106 PM EDT Sun Aug 07 2022 Valid 12Z Wed Aug 10 2022 - 12Z Sun Aug 14 2022 ...Heavy rainfall/flash flooding threat for the Ohio/Tennessee and Lower Mississippi Valleys and south-central Appalachians... ...Monsoonal moisture/rainfall threat continues for the Southwest and south-central Great Basin/Rockies this week... ...Overview... It remains the case that the overall weather pattern across the contiguous U.S. through the latter half of this week is forecast to amplify into a trough-ridge-trough pattern, as shortwaves combine to deepen a trough in the East, an upper low off the West Coast lifts northeastward toward the Pacific Northwest, 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 into the Appalachians/Mid-Atlantic and Northeast Wednesday, with scattered convection possible farther south as well. Meanwhile, persistent monsoonal moisture looks to continue across the Southwest and south-central Great Basin/Rockies this week. ...Guidance Evaluation/Predictability Assessment... Model guidance remains quite agreeable with the upper high/ridge persisting and meandering a bit across the central U.S. through the week into next weekend, and also agrees upon the trough deepening across the East late week, with detail differences decreased from past runs oevr medium range time scales. This bolsters pattern forecast confidence. The WPC medium range product suite was primarily derived from a composite blend of now overall well clustered gudiance from the latest GFS/ECMWF/UKMET/Canadian and GEFS/ECMWF ensembles along with the 13 UTC National Blend of Models and WPC product continuity. Targeted changes to the 13 UTC NBM QPF included some increase of afternoon/evening convective amounts over the West but in particular across the central Gulf of Mexico coast mid-later this week and with frontal passage across the Upper Midwest/Great Lakes next weekend. ...Weather/Hazards Highlights... As the medium range period begins 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 movement 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, as they have received abundant rainfall recently and are sensitive to additional rain amounts, so a Slight Risk remains in the experimental Day 4 ERO. The Northeast/New England also may receive heavy rain that could cause flash flooding given a sharpening trough aloft providing upper level support and above average moisture, but model spread in the exact placement of the heaviest rainfall precluded adding a Slight Risk. 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. In this pattern there is also increased potential for locally enhanced lead rains across the lower MS Valley/central Gulf Coast mid-late week with moist flow and slow cell translation. Meanwhile, monsoonal moisture (that could be enhanced due to T.D. Nine-E) continues to impact the Southwest with rainfall, with a trend toward increasing chances for rain farther north as the moisture plume expands into the Intermountain West/Great Basin and the Rockies, with some locally heavy totals possible. Very warm to hot temperatures around 10-15F above average, though not quite to record-breaking levels, are forecast across the northern/central Plains through the latter part of the week, with a slight eastward trend as the upper high moves that direction. 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 next weekend. Tate/Schichtel 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