Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM 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... ...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... Model guidance has stabilized for the most part with the timing of the eastern Pacific upper low coming into southwestern Canada, opening into a shortwave, and moving eastward through south-central Canada early next week, with a generally slower track than some models showed a day or so ago. The 18Z GFS was somewhat faster than consensus, so preferred a blend incorporating the 12Z GFS and other 12Z guidance for this feature. 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. The 12Z CMC in particular suppressed the ridge more than other models in the Midwest. Meanwhile farther east, models agree upon deepening troughing late this week. But there are some differences with distribution of energy within the trough and potential for a closed low at times as shown by some deterministic guidance like the ECMWF and GFS. No models from the 12/18Z cycle seemed to be particular outliers in the East, however. Given the fairly good agreement in the overall pattern, but with various details still up in the air (literally), the medium range forecast used a blend of the 12/18Z deterministic models early and then incorporated the GEFS and EC ensemble means with gradually increasing proportions to about 50 percent by day 7 for the WPC mass fields. Once again QPF was increased over the almost zero NBM values across the Midwest Friday into the weekend as frontal boundaries come in west of the high and models show potential for rain. ...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. Rain amounts will be dependent on how much moisture progresses onshore, but with the potential for slow-moving storms, the chance of flooding is nonzero. 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 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