Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1200 PM EDT Thu Jun 21 2018 Valid 12Z Sun Jun 24 2018 - 12Z Thu Jun 28 2018 ...North-Central U.S. Heavy Convective Rainfall Pattern... ...Guidance/predictability Assessments with weather highlights... Models and ensembles continue to show excellent agreement that a split flow upper-level pattern across North America will gradually become more consolidated by the middle of next week as heights are forecast to increase over the central and eastern U.S. Until then, a couple of upper-level shortwaves are expected to track generally from the northern Rockies across the central Plains and then lifts out into the Great Lakes. This modestly progressive pattern appears to support the amplification of mesoscale convective systems over the central Plains early next week where locally excessive rainfall is possible. By the middle of next week, models agree that the main energy associated with the shortwaves will weaken and lifts toward the Great Lakes as a Pacific front dips into the northern Plains. Some remnant thunderstorms should push into the Ohio Valley into the Appalachians by the middle of next week. Over the southeastern U.S., a weakening front should promote showers and thunderstorms from Florida westward into the central Gulf coast. Meanwhile, the GFS has begun to indicate the possibility of a surface low lingering just off the Carolina coast along the dying front toward the middle of next week. Accordingly, the WPC medium range morning product suite was derived from a composite blend of the 00Z ECMWF and 06Z GFS trending toward their ensemble means through Day 7. This maintains excellent WPC continuity. Kong WPC medium range forecasts of 500 mb heights, surface systems, weather grids, quantitative precipitation, and winter weather outlook probabilities are found at: http://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif http://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif http://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html http://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml http://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4