Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1201 PM EDT Fri Apr 26 2019 Valid 12Z Mon Apr 29 2019 - 12Z Fri May 03 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 fairly persistent pattern will develop in the medium range period, with a deep upper low in north central Canada gradually retrograding a bit westward later in the period, and troughing over the northwestern U.S. extending southward. A subtropical ridge is 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 some typical uncertainty in timing and placement of shortwaves moving across the general troughing pattern in the west and central U.S. WPC used a multi-model deterministic blend of the 00Z and 06Z GFS, 00Z UKMET, and 00Z ECMWF early in the period, then leaning toward the EC and GEFS means later in the week as uncertainty develops in the deterministic runs regarding the upper low in western Canada and potentially shearing out its energy, which affects the downstream features. Run to run inconsistency remains high, so stayed with the means for now. ...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 Great Basin and central/northern Rockies early in the period. 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 the 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 in the Ohio Valley and into the northern Mid-Atlantic to Lower Great Lakes region as well. Flooding will be 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 snows for portions of the Northern High Plains with low genesis and approach. Tate/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