Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Fri Aug 05 2022 Valid 12Z Mon Aug 08 2022 - 12Z Fri Aug 12 2022 ...Monsoonal pattern remains active across the Southwest with additional heavy rainfall likely while threat of heavy rain increases over northern New England Monday to Tuesday... ...Overview... The overall weather pattern across the contiguous U.S. next week will likely 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, while an upper high nudges eastward from the central Rockies into the central 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 Midwest to the Ohio and Tennessee Valleys early next week but training activities along a west-to-east front could lead to a focus of heavy rain across northern New England Monday to Tuesday. Meanwhile, persistent monsoonal moisture looks to continue across portions of the West leading to additional heavy 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 this morning are quite agreeable with one another with respect to the aforementioned synoptic evolution for next week. The largest model spread pertains to the timing of the upper low off the West Coast as it is forecast to move into the Pacific Northwest late next week. Both the deterministic ECMWF and GFS indicate a faster landfall of the upper low than their ensemble means. The CMC was the opposite in this respect (with the deterministic solution being slower). By next Friday, the ECMWF/EC mean are the fastest solutions in terms of taking the upper trough and associated low pressure system well into central Canada in contrast with the slower solutions from the GFS and CMC as well as earlier ECMWF runs. 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. The results show good continuity with the previous forecast package. ...Weather/Hazards Highlights... As the medium range period begins Monday, an axis of locally heavy rain and thunderstorms ahead of a cold front is expected to continue pushing southeastward from across the lower Great Lakes and the Midwest into the Ohio Valley. Meanwhile, a axis of heavy rain is possible across northern New England Monday into Tuesday as a west-to-east oriented wavy front could aid cell training activities. Showers and storms with locally heavy rain will shift southeast each day as the front progresses, sliding across the Eastern Seaboard and lower Ohio/Tennessee Valleys/southern Appalachians Tuesday-Wednesday. Some heavy rain rates and amounts could lead to potential for flash flooding in these areas, especially over sensitive locations that have received abundant rainfall recently, though some waffling in model guidance lowers confidence in the details. Activities should become more scattered as they settle into the Southeast Thursday-Friday while cooler and drier air moves into the Northeast. Meanwhile, monsoonal moisture continues to impact the Southwest with enhanced rainfall. Another wet day is likely on Monday, with some indications of a focus near the Colorado/New Mexico border (where conditions are already quite wet) that has prompted a Slight Risk issuance in the experimental Day 4 ERO. While rain amounts may gradually lessen in this area as the week progresses, the moisture plume is likely to expand farther north into the Intermountain West and Great Basin with some locally heavy totals possible here as well. A Slight Risk has been introduced for northern New England. Very warm to hot temperatures around 10-15F above average, though not quite to record-breaking levels, are forecast to shift from the Northwest Monday into the northern and then central Plains as the workweek progresses and the upper ridge axis moves east. Farther east, slightly above average highs in the Northeast/Mid-Atlantic early in the workweek will moderate to right around normal behind the cold front, while some below normal highs are possible in the Ohio and Tennessee Valleys. Given the rainfall and cloudiness over the Southwest and Great Basin, highs are likely to be several degrees below normal there. 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