Extended Forecast Discussion NWS Weather Prediction Center College Park MD 356 PM EDT Mon Aug 08 2022 Valid 12Z Thu Aug 11 2022 - 12Z Mon Aug 15 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 combine to deepen 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 stalling and approaching the Gulf Coast 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. ...Guidance Evaluation/Predictability Assessment... Guidance had stabilized for the most part with the evolution of an eastern Pacific upper low coming into southwestern Canada, opening into a shortwave, and moving eastward into Canada early next week, but timing variance has re-emerged. Prefer a solution on the slower side of the full envelope of guidance given trends and history. Meanwhile, the upper high in the central U.S. appears well handled in the models, though with some uncertainty on how much it could be suppressed by energy rounding the ridge, especilaly by the weekend. The CMC in particular suppressed the ridge more than other models in the Midwest and showed less amplitude of the lingering eastern U.S. upper trough. Prefer a more amplified solution. Accordingly, the WPC medium range product suite that was primarily derived from a composite GFS/ECMWF/Canadian/UKMET model blend and the National Blend of Models (NBM) for Thursday/Friday was quickly transitioned to a GFS/ECMWF and GEFS/ECMWF ensemble mean blend along with the NBM through the weekend into early next week. This solution follows aforementioned preferences. The main adjustment today to NBM QPF was to increase rainfall amounts along the Gulf Coast later this week. ...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, which could produce locally heavy rain especially along the coast. Slow-moving and repeat storms will be fueled by lead and boundary pooled deep moisture and upper diffluence/vertical wind profile. Rain chances are likely to continue across much of Florida into the weekend as the front stalls. Farther north, the cold front should clear out most rainfall from the Mid-Atlantic, but some rain could remain across the Northeast as a low along the front may linger nearby. Meanwhile, monsoonal moisture (that could be enhanced due to T.S. Howard) continues to impact the Southwest into parts of the Great Basin and into the Rockies with rainfall, 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 drifts that direction. Highs nearing 100F are 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. 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. Tate/Schichtel Hazards: - Heavy rain across portions of the Southwest, the Great Basin, and the Northern and Central Rockies, Thu-Mon, Aug 11-Aug 15. - Heavy rain across portions of the Central Gulf Coast and Florida, Thu-Sat, Aug 11-Aug 13. - Flooding possible across portions of the Upper Mississippi Valley. - Flooding occurring or imminent across portions of the Ohio Valley and the Northern Plains. - Flooding likely across portions of the Middle Mississippi Valley. - Excessive heat across portions of the Northern Rockies and Northern and Central Plains, Thu-Sat, Aug 11-Aug 13. 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