Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1151 AM EDT Mon Jul 23 2018 Valid 12Z Thu Jul 26 2018 - 12Z Mon Jul 30 2018 ...Southwest/West heat wave easing by late week... ...Heavy rainfall threat shifts back to the Central Rockies/Plains then Mid-MS Valley/Mid-South... ...Guidance/Uncertainty Assessment and Weather Threats... Deep troughing across the Eastern U.S. at the end of the short range gets replaced with additional amplified mid-upper level troughing working its way across the Great Lakes and into the Northeast days 3-5. Periods of heavy convective rainfall associated with pooling moisture along and ahead of a surface front can be expected, with local runoff issues possible (especially given the very wet antecedent conditions). Additional activity will trail southward along or off the east coast and across Florida. Meanwhile, a hot mid-upper level ridge and record maximum temperatures over the Southwest and into the West will ease by later this week, with record high minimum temps also possible given lingering monsoonal moisture through the week. A series of impulses rotating within and around the upper ridge dig southward into the central states to interact with surface boundaries, instability, and favorable low level moisture inflow/convergence. Forecast spread begins to increase by day 6/7 with additional waves rotating southward into central Canada and upper level trough redevelopment from the north-central U.S. into the Mississippi Valley. Recent runs of the deterministic GFS/ECMWF have sort of flip-flopped between a more amplified/progressive wave in central Canada, or a more suppressed/slower wave. The GEFS/EC ensemble means are fairly consistent (at least for day 7 standards) with showing a solution more in the middle or maybe slightly weighted towards more amplified, which is better supported by Southwestern U.S. ridge position, recent eastern U.S. trough history, and previous shift continuity. Regardless, this pattern would support multiple episodes of heavy convection from the central Rockies/Plains into the Mid-Mississippi/Ohio/Tennessee Valleys. Heavy rainfall and repeat cells may lead to a locally excessive rainfall threat. This cycle of the medium range forecast suite used a blend of the well clustered GFS/ECMWF/UKMET for days 3-5, with increased contributions from the GEFS/ECMWF by days 6-7. Days 6-7 were also slightly more weighted with the latest deterministic GFS run in order to show a slightly more amplified wave (as discussed above) and a better match to previous shift continuity. Santorelli 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