Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Tue Aug 09 2022 Valid 12Z Fri Aug 12 2022 - 12Z Tue Aug 16 2022 ...Monsoonal moisture/rainfall threat continues for the Southwest and Intermountain West/Rockies this week, with some localized heavy rain possible for the Gulf Coast states as well... ...Excessive heat threat from the interior Northwest to the north-central Plains... ...Overview... A fairly stagnant trough-ridge-trough pattern is forecast later this week into early next week across the contiguous U.S., as shortwaves deepen and then maintain a trough in the East, an upper low off the West Coast lifts northeastward into British Columbia, and an upper high meanders near the central/southern High Plains. A cold front or two approaching the Gulf Coast and stalling will provide a focus for moisture and rain/thunderstorms there and lingering across much of Florida into early next week. Meanwhile, persistent monsoonal moisture looks to continue across the Southwest and expanding into the Intermountain West and Rockies this week into next week. ...Guidance Evaluation/Predictability Assessment... Broad consensus for amplified patterns over the East and West coasts with an central U.S. ridge wane toward the end of the period. A general model blend of deterministic guidance was utilized through day 4 with an ensemble introduction by day 5 and continuing through day 7. On day 3, the 00z EC/CMC/UK and 06z GFS were used as they agreed on the overall trough-ridge-trough pattern across the lower 48. We continued this blend into day 4 with some 00z GFS included to account for timing and intensity spread in the upper trough over the Pacific Northwest/British Columbia. The 00z ECE and 06z GEFS were incorporated into the general model blend on day 5 to account for uncertainty associated with an embedded shortwave propagating through southern Canada and the Northern Plains. Day 6 was heavily weighted toward the 00z EC/ECE due to reasonable and run-to-run consitency of the upper trough over the East Coast and the central U.S. ridge with which the 06z GFS/GEFS were a bit more inconsistent. The 00z CMC was a bit too intense with respect to an upper vort over southern Wyoming. The 06z GFS/GEFS and 00z CMCE were also incorporated into the blend, albeit with lower weighting. Day 7 was a blend of the ensembles with a bit of 00z EC included. The main area of uncertainty on day 7 is in the deterministic 06z GFS, which has an anomalous closed low centrered over the Upper Great Lakes/Michigan. ...Weather/Hazards Highlights... Moisture streaming ahead of a couple of cold fronts moving into the Southeast and toward the Gulf Coast late this week will produce rain and thunderstorms in those areas. This could cause localized flooding issues since storms should be slow-moving and may train over the same areas. Rain chances are likely to continue across much of Florida into early next week as the front stalls. Farther north, the cold front should clear out most rainfall from the Mid-Atlantic and likely the Northeast as well, but dependent on how close to the New England coast a low along the cold front sits. Shortwave impulses rounding the ridge could lead to rain and storms across the Midwest/Upper Great Lakes into the Ohio Valley this weekend into early next week, but with low confidence on the specifics. Meanwhile, monsoonal moisture continues to impact the Southwest into parts of the Great Basin and into the Rockies with rainfall through the medium range period. Some locally heavy totals are possible and a Slight Risk of flash flooding has been added to the experimental Day 4 ERO. Very warm to hot temperatures around 10-15F above average, though not quite to record-breaking levels, are forecast across interior portions of the Northwest and into the Northern/Central Plains through the latter part of the week, and lasting across the Central Plains and parts of the Mid-Mississippi Valley this weekend into early next week. A slight southern shift is expected with time, leading to highs nearing/reaching 100F forecast early next week in the central/southern Plains. Farther east, below normal highs are possible in the east-central U.S. behind the cold front, with the most persistent cooler than average weather in the Ohio and Tennessee Valleys. The Mid-Atlantic and Northeast should experience clear and comfortable temeratures this weekend. Given the rainfall and cloudiness over the Southwest and Great Basin, highs are likely to be several degrees below normal there through early next week. Kebede/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