Extended Forecast Discussion NWS Weather Prediction Center College Park MD 226 AM EDT Sat Apr 27 2019 Valid 12Z Tue Apr 30 2019 - 12Z Sat May 04 2019 ...Heavy rain and the potential for flooding and flash flooding are expected for parts of the Southern Plains and Lower/Middle Mississippi Valley to Ohio Valley... ...Overview and Assessment of Model/Ensemble Guidance and Predictability... A reasonably persistent flow pattern develops next week over the U.S.as a deep north-central Canadian upper low gradually retrogrades to western Canada. Northern stream troughing digs underneath into a wintry northwestern U.S. as an initially closed southern stream E-Pacific low ejects with various timings inland into the Southwest. Prefer a southern stream progression on the slower side of the full envelope of solutions considering the initially closed nature of the low, with the GFS more progressive than the ECMWF/UKMET/Canadian. A series of troughs subsequently eject northeastward from the Plains through the MS/OH Valleys to the Northeast to support wet low development on a slow moving front. This occurs overtop a subtropical ridge forecast to build over the Southeast through midweek before pushing out by Friday. The overall pattern seems to be generally well handled by the models, with typical uncertainty in the timing and placement of shortwaves from a general troughing pattern in the west and central U.S. WPC used a multi-model deterministic composite blend Tue-Thu, with transition to the GEFS/ECMWF ensemble means later week consistent with growing uncertainty and run to run inconsistency. ...Weather Highlights/Threats... Passage of multiple shortwaves/height falls in both northern and southern streams will generate some enhanced rains and mountain snows for portions of the central/northern Rockies early next week. These systems will progress downstream and a main weather focus will develop over the central U.S. Moisture inflow/pooling into a persistent/slow moving/wavy front will focus multiple rounds of showers and thunderstorms, with some potential for severe weather and areas of heavy rainfall. The strongest signal for heavy rainfall of multiple inches will be from the Southern/Central Plains to the Lower/Mid-Mississippi Valley, with some potential for heavy rain to spread over the Ohio Valley and northern Mid-Atlantic/Lower Great Lakes region. Flooding remains possible as particularly the Mississippi Valley has had flooding concerns for weeks, and with the convective element of the precipitation, flash flooding is possible as well. On the northern fringe the precipitation, sufficient cold air may be in place to support some snows for portions of the Northern High Plains with low genesis and approach. Schichtel Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml