Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1156 AM EDT Thu Jul 26 2018 Valid 12Z Sun Jul 29 2018 - 12Z Thu Aug 02 2018 ...Heat wave lingers over the West... ...Heavy rainfall threat to spread from the Central Plains to Mid-South then the Southeast/Eastern U.S... ...Pattern Overview and Weather Highlights/Threats... The ridge over the western U.S. will keep much of the West Coast, Southwest and Great Basin hot and mostly dry. With the heat wave persisting, many locations will likely have heat advisories and/or excessive heat warnings in effect. Low humidity during the afternoon, along with poor recoveries overnight, conditions near critical fire danger may persist. Active impulses linger in the Southwest/Southern Rockies and over the ridge and will dig into the central U.S. in favorable upper diffluence to interact with surface boundaries, instability, and favorable low level moisture inflow/convergence. The ridge over the Atlantic Ocean will retrograde back toward the Gulf Stream, which will result in the trough sandwiched over the central U.S. to dig further south with little eastward progression. Otherwise, a weak longwave trough offshore the Pacific Northwest early next week gradually ejects inland to moderate flow. As the trough digs through the Mississippi Valley early next week frontal lows will develop with gradual frontal system progressions downstream over the E-Central U.S. Expect multiple episodes of heavy convection from the Central Rockies/Plains through the mid-lower Mississippi Valley/Mid-South this weekend whose threat spreads over much of the East-Central to Southeast/eastern U.S. next week. Slow bands of heavy rainfall tracking over the same area will keep threat for widespread excessive rainfall elevated in the extended periods. ...Guidance/Uncertainty Assessment... The WPC medium range product suite was derived from a blend of the 00 UTC ECMWF/GFS, 06 UTC GFS and the 00 UTC NAEFS/GEFS/ECMWF ensembles. The ECMWF continue to be more amplified than its counterparts and maintained a slightly high weighting than the 00/06 UTC runs of the GFS. Weighting of the ensemble means increase incrementally through the end of the extended period. Campbell 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