Extended Forecast Discussion NWS Weather Prediction Center College Park MD 246 PM EDT Thu Aug 11 2022 Valid 12Z Sun Aug 14 2022 - 12Z Thu Aug 18 2022 ...Monsoonal moisture/rainfall threat continues for the Southwest and Intermountain West/Rockies... ...Excessive heat threat across the Plains, with warming temperatures in the Northwest next week... ...Overview... The medium range period will begin Sunday with a continued trough-ridge-trough pattern across the lower 48. As next week progresses, there should be a trend toward the upper high/ridge expanding into the West, leading to well above average temperatures in the Northwest. The ridge aloft with embedded shortwave energy will also continue to support monsoonal moisture streaming into the Southwest, Intermountain West, and Rockies through the week, with rain eventually spreading into portions of the Plains and Mississippi Valley. Meanwhile the trough across the East may deepen and close off an upper low around midweek, which could cause multiple days of rainfall in the Northeast, but dependent on the position of the upper low and the associated surface low/fronts, which remain uncertain at this point. ...Guidance Evaluation/Predictability Assessment... There was a bit more uncertainty with the synoptic pattern compared to yesterday, particularly with respect to the eastern U.S. trough. The trough-ridge-trough pattern was captured well by the latest guidance, though. A general model blend of the 00z EC/UK/CMC and 06z GFS was utilized on days 3 and 4 with the 00z EC being favored through day 5 due to a more consistent signal and reasonable approach to the southern ridge and eastern trough. Models, including the latest 13z NBM, have trended dryer since overnight with respect to the qpf produced by the eastern trough over parts of the coastal Northeast on days 4-6. The 00z ECE/CMCE were incorporated into the gmb on day 5 to smooth out small scale discrepancies found in the western ridge axis. The ensembles were favored through the rest of the period. ...Weather/Hazards Highlights... Parts of the West have seen persistent monsoonal moisture over the past couple of months, and next week will continue that pattern as anomalously high moisture streams into the Southwest, Great Basin, and Rockies in conjunction with small-scale shortwave energy to produce rain and thunderstorms, particularly in the afternoon and evening hours. Slight Risks of excessive rainfall are in place for portions of the Desert Southwest on Sunday and the Central Rockies on Monday, where current forecasts show the best chances for heavy rainfall. Heavy rain amounts look to continue through midweek in the Central Rockies. There are increasing chances for rainfall to spread into parts of the Central/Southern Plains and Mississippi Valley as the week progresses. Elsewhere, the Gulf Coast and into Florida could see scattered storms with a moist airmass and a couple of frontal boundaries. Then as a surface low is currently forecast to track across the Ohio Valley through the Mid-Atlantic toward the Northeast, rain is forecast for those areas. There's increasing confidence in a multi-day rain event occurring for much of the coastal Northeast, from New Jersey up to Maine through mid-week. Very warm to hot temperatures around 10-15F above average, though mainly not to record-breaking levels, are forecast across the Central Plains Sunday into Monday, with a gradually moderating trend Tuesday onward yielding below normal highs. As the upper ridge expands into the Northwest, this will warm up temperatures there and cause highs 10-20F above normal for Tuesday-Thursday. Meanwhile, below normal highs are expected in the east-central U.S. behind the cold front, with the most persistent cooler than average weather in the Ohio and Tennessee Valleys toward the Mid-Atlantic. Given the rainfall and cloudiness over the Southwest and Great Basin into the Rockies, highs are likely to be several degrees below normal there through much of 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