Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1227 PM EDT Fri Jul 27 2018 Valid 12Z Mon Jul 30 2018 - 12Z Fri Aug 03 2018 ...Hot temperatures over the West gradually moderating... ...Heavy rainfall threat extending from the central Plains/MS Valley to Southeast/Eastern U.S... ...Pattern Overview and Weather Highlights/Threats... Much of the central and eastern U.S. will have a multi-day threat of convection/heavy rainfall; leading to an elevated risk for flooding, especially for the South Appalachian region. Energy dropping through the Plains as of early next week will carve out another eastern U.S. upper trough that should achieve its greatest depth around midweek before trending weaker. A steady influx of Gulf moisture feeding into this system will increase precipitation efficiency. Areal averages over the course of 7 days are forecast to be 2 to 4 inches, with isolated amounts exceeding 5 inches for the Southeast and Mid-Atlantic regions. Some areas of moderate-heavy rainfall may extend into parts of the Great Lakes/Appalachians/Mid-Atlantic. The pattern will promote below normal temperatures from the Plains into the Southeast with greatest negative anomalies of minus 5-15F most likely over parts of the Plains early in the week. Much of the Southwest will continue to be hot although temperatures will be moderating through the extended periods. The ridge over the West will become slightly flatten as a trough/low pressure persists near the the Pacific Northwest Coast. By late week this energy should support Northern Plains low pressure with a corresponding increase in convection. Highest anomalies overall should be over the Northwest on Mon-Tue. The Great Basin/Southwest will likely remain quite warm for mins through the end of the week with highs tending to be more modestly above normal (though still hot on an absolute basis). The Northwest should trend below normal for highs by the latter half of the week. ...Guidance/Uncertainty Assessment... The latest guidance continues with the synoptic pattern of a ridge over the West, a digging trough over the central U.S. and a retrograding ridge over the Atlantic/East Coast. Differences on the timing and placement of storm specific details for the east-central U.S. trough in part due to how far west the ridge reaches the East Coast. The deterministic/ensemble models have continued issues in resolving the area of low pressure offshore of the Pacific Northwest Coast, therefore confidence remains low over this region. Possibilities range from a fairly cohesive low/shortwave whose timing varies by solution to some energy ejecting ahead while lingering energy remains near the Pacific Northwest. At least the models/means share the common idea of a general areas of surface low pressure over/near the northern Plains late in the period. The initial forecast started with 00 UTC ECWMF/CMC/UKMET and 06 UTC GFS compromise through Tuesday July 31st. From Wednesday August 1st the 00 UTC NAEFS/GEFS/ECENS was introduced into the blend and increased in weighting gradually through the end of the extended period on Friday August 3rd. Campbell/Rausch WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml