Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1156 AM EDT Fri Apr 05 2019 Valid 12Z Mon Apr 08 2019 - 12Z Fri Apr 12 2019 ...Overview and Guidance Assessment/Preferences... A moderately progressive pattern is expected across the CONUS during the medium range with splitting of flow across the West resulting a series of southern stream systems traversing the nation. The first of these should cross the lower Mississippi Valley/Southeast Mon-Tue. The second and more significant of these features should move into the West Coast Mon-Tue before amplifying across the Rockies on Wed and perhaps developing a closed upper low across the central U.S. Wed night-Thu. Finally, a third upper-level wave should amplify along the West Coast Thu-Fri as the strong central U.S. system moves into the lower Great Lakes. Meanwhile, a number of lower amplitude northern stream shortwaves will traverse areas from the Northern Plains/Midwest to the Northeast. In general a blend of the 00Z ECMWF/UKMET/CMC was preferred as a forecast starting point during days 3-5 (Mon-Wed). These solutions handled significant features similarly during this time period. The shortwave reaching the West Coast during this time frame showed the most substantial differences among the guidance, with the GFS continuing to show a slower progression/later arrival to the coast relative to the preferred solutions. The GFS continued to lag the preferred consensus solution even as the western system reaches the central Rockies Tue night-Wed and significant cyclogenesis commences across the Central High Plains. As a strong low pressure system likely crosses from the Central Plains to the Midwest Wed into Thu, there was relatively good clustering among ECENS and CMCE members in the vicinity of the deterministic 00Z ECMWF. The GFS begins to suffer from the opposite issue to earlier in the period, showing a much weaker system aloft and racing the surface low quickly eastward into the Ohio Valley, with the CMC somewhere between the ECMWF and GFS. Given the good clustering around the ECMWF, the forecast during days 6-7 (Thu-Fri) was comprised of a three-part blend including the ECMWF and the ECENS/NAEFS ensemble means. This approach also worked well for the next round of energy dropping southward/amplifying across the western U.S. late next week. Model solutions have shown a high degree of run-to-run variability with that feature, varying between a more open wave or one that quickly deepens into a closed upper low over southern California. With ensemble means similar here, a majority ensemble-based approach was favored. ...Weather Highlights/Hazards... Showers and thunderstorms with locally heavy rains are possible from the Southeast/Tennessee Valley to the Mid-Atlantic Mon-Tue as the first southern stream shortwave/low pressure system traverse those areas. A northern stream system may also bring a round of snow to portions of northern New England Mon/Mon night. The second and most significant southern stream system during the period should produce widespread rains and mountain snows (some potentially heavy) from California to the Pacific Northwest and then inland across the central/northern Rockies Mon-Tue. As the system reaches the central U.S. by the middle of next week, a band of dynamically forced precipitation is expected to develop from the Northern High Plains to the Midwest and Great Lakes. While the delineation of precipitation types is unclear at this time, a band of potentially heavy snow appears probable north and west of the surface low track, with a transition zone and areas of potentially heavy rain as well. Relatively weak moisture return and a strong capping inversion in the warm sector of the system should keep showers and thunderstorms less extensive in coverage than would otherwise be expected, but any convective activity that is able to develop could be potentially strong given the dynamic nature of the low pressure system. Warm temperatures are expected across much of the central and eastern U.S. during the early to middle portion of next week ahead of the significant low pressure system. High temperatures ranging from 10 to 20 deg F above average are possible Mon-Wed over a large area, with the greater anomalies across the Plains. Colder air and further amplification of upper troughing across the West in the wake of the mid-week system will support below average temperatures, with highs 5 to 15 deg below average across much of the interior West by Wed and into the Central/Northern Plains by Thu-Fri. Ryan 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