Extended Forecast Discussion NWS Weather Prediction Center College Park MD 439 PM EDT Fri Apr 24 2020 Valid 12Z Mon Apr 27 2020 - 12Z Fri May 01 2020 ...Extended Period of Much Above Normal Temperatures Across the West... ...Stormy Weather to Affect the Central and Eastern States... ...Guidance/Predictability Assessment... Negatively tilted shortwave energy over the Northeast is well agreed upon by the latest guidance to start the medium range period such that a multi-model deterministic blend was used for day 3 /Monday/. However, quickly by day 4 guidance strays from one another such that forecast confidence drops to average at best as there continues to be speed/timing issues with the parade of shortwaves skirting through the northern U.S. in the overall fast quasi-zonal flow on day 3/4. By mid-week /day 5/, shortwave energy deepens and the upper level pattern becomes more amplified featuring a digging trough over the Great Lakes region and building heights over the northern Rockies. The GFS runs continue to be too fast/progressive with the developing shortwaves and there has been better continuity and consistency seen in the ECMWF/CMC solutions and to some degree the UKMET. By the end of the forecast period, shortwave energy will attempt to break down the ridge over the Pacific NW while the eastern U.S. continues to see anomalous troughing. With somewhat favorable agreement in this pattern, the WPC blend by day 6/7 incorporated a majority from the ECENS/GEFS but also retained some of the 00Z ECMWF/GFS for detail and continuity. ...Weather/Hazard Highlights... At the beginning of the medium range period, low pressure off the New England coast will move toward the Canadian Maritimes, with some coastal/maritime threats and lingering locally heavy precipitation back over the Northeast including snow over the cold interior and higher elevations of New England. The pattern of a western ridge/eastern trough is expected to largely continue through the week, and begin to amplify more as troughing digs again over the Great Lakes region. This will support unsettled weather with a parade of low pressure systems across the central/eastern U.S.This developing system should produce an expanding area of meaningful rainfall mid-week, with enhanced precipitation expected to spread from the MS Valley/Midwest Tue through the Appalachians/Northeast Wed into Thu. As heavy rainfall is possible in some saturated areas around the lower MS Valley/Mid-South by Tue, flash flooding/excessive rainfall remains a concern. The western ridge will also support building much above normal temperatures across the Desert Southwest that will spread to much of the southern/central Rockies and into portions of the Plains by mid/late week. The hottest readings over the Desert Southwest will top out in the 100-110F range. Taylor Hazards: - Heavy precipitation across northern Maine, Mon, Apr 27. - Heavy rain across portions of the lower to middle Mississippi Valley, and into the southern Plains, Mon-Tue, Apr 27-Apr 28. - Heavy rain across portions of the Northeast and down into the central Appalachians, Wed-Thu, Apr 29-Apr 30. - Flooding possible across portions of the northern Plains, the Tennessee Valley, the middle Mississippi Valley, the Southeast, the Great Lakes, and the Ohio Valley. - Flooding occurring or imminent across portions of the Deep South, the Southeast, and the northern Plains. - Flooding likely across portions of the central Plains, the Southeast, the middle Mississippi Valley, and the Tennessee Valley. - Much above normal temperatures across a large portion of the interior western U.S., Mon-Fri, Apr 27-May 1. - Much above normal temperatures across much of California into Oregon, Mon-Thu, Apr 27-Apr 30. - Much above normal temperatures across much of the central and southern High Plains, Mon-Tue, Apr 27-Apr 28, and Thu-Fri, Apr 30-May 1. 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