Extended Forecast Discussion NWS Weather Prediction Center College Park MD 243 AM EDT Wed May 01 2019 Valid 12Z Sat May 04 2019 - 12Z Wed May 08 2019 ...Guidance/Predictability Assessment ... WPC medium range surface/fronts and 500 mb progs were mainly composed from a composite of compatable GFS/ECMWF/UKMET/Canadian mid-larger scale mass field guidance this weekend. Transitioned to an ensemble mean based forecast early-mid next week amid growing forecast spread and uncertainty. This blended solution acts to mitigate embedded smaller scale impulse timing and convection genesis uncertainties and maintains good overall WPC continuity. The WPC forecast did favor ECMWF/ECMWF ensembles precipitation that better fit the flow in showing more southward convective tendancies into deepening moisture. ...Weather Highlights/Threats... A slow moving and wavy trailing front will pool moisture to fuel a risk of locally heavy rains/thunderstorms with cell training and a local runoff issue focus from the Lower Mississippi Valley to the Mid-Atlantic this weekend. Upstream, closed low/trough energy and height falls are expected to move inland into CA/Southwest early next week in the split southern stream. This may support scattered CA to Great Basin/Rockies convection. Flow progression may then renew lead convective focus downstream over the south-central U.S. Meanwhile, northern stream systems will meanwhile progress over southern Canada and effect the U.S. northern tier. These would support precipitation/convection ahead of a cooling main closed low/trough and lead weather focusing surface frontal systems. This amplified main system will track from s-central Canada this weekend to eastern Canada early next week. A stalling trailing front underneath into will periodically focus activity over the northern Rockies, central Plains, and from the Midwest to the Northeast. This may include some May snows for the Rockies and from northern Minnesota to the Upper Great Lakes. 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