Extended Forecast Discussion NWS Weather Prediction Center College Park MD 151 AM EDT Tue Apr 30 2019 Valid 12Z Fri May 03 2019 - 12Z Tue May 07 2019 ...Flooding/Flash Flooding Threat Lingers for the Southern Plains/Lower Mississippi Valley... ...Guidance/Predictability Assessment and Weather Highlights/Threats... The WPC medium range product suite was mainly derived from a composite of reasonably well clustered GFS/ECMWF/UKMET/Canadian and ensemble mean mid-larger scale guidance. This blended solution acts to mitigate embedded smaller scale impulse timing and convection genesis uncertainties and maintains good overall WPC continuity with respect to potential weather related hazards. A lead and wavy frontal system with moderate precipitation will progress Fri/Sat across the East as powered by an ejecting shortwave trough aloft. A wavy trailing front will stall across the U.S. southern tier and pooled moisture and convection offers a daily threat of heavy rains/thunderstorms and cell training/locally enhanced runoff issues with hard to time southern stream impulse passages. Pacific closed low/trough energy and height falls are also expected to work inland into CA by early next week in this split southern stream. This may support scattered Southwest to Rockies convection and then renew lead convective focus downstream over the south-central U.S. Strong to severe thunderstorms with some heavy rain and flash flooding/flooding potential will periodically threaten the Southern Plains and Lower Mississippi Valley in this lingering pattern. Flooding remains possible as particularly the Mississippi Valley and vicinity has had flooding concerns for weeks, and with the convective nature of the precipitation flash flooding is possible as well. Meanwhile, leading northern stream shortwaves overtop are expected to progress from the Northwest eastward across the U.S. northern tier. This will support modest system/precipitation development in advance of a cooling/unsettling main closed low/trough and lead weather focusing surface frontal system. This amplified system may track from western Canada Fri to s-central Canada/Upper Midwest Sun to eastern Canada and the Northeast in about a week. The baroclinic zone with the stalling trailing front may periodically focus impulse driven convection mainly over the northern Rockies, central Plains, and Ohio Valley. 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