Extended Forecast Discussion NWS Weather Prediction Center College Park MD 238 AM EDT Wed Apr 28 2021 Valid 12Z Sat May 01 2021 - 12Z Wed May 05 2021 ...Weekend south-central U.S. heavy rainfall/convection threat... ...North-central to east-central heavy rainfall/convection threat early next week... ...Guidance/Predictability Assessment and Preferences... Models and ensembles may have converged upon a more well clustered solution through much of the medium range period, bolstering forecast confidence to average or better levels. The WPC product suite was primarily derived from a composite blend of the 12 UTC ECMWF/UKMET/Canadian and ECMWF ensembles. Recent GFS/GEFS runs trended in this direction, but were more progressive overall until finally the latest 00 UTC runs. ...Weather/Hazards Highlights... A storm over the Canadian Maritimes Saturday will support strong winds back over the Northeast as an amplified northern stream upper troughing working over the region. A wavy trailing front will stall down across Florida and the Gulf of Mexico and may focus some locally enhanced weekend rainfall, but guidance has backed off on amounts. Meanwhile, slow moving southern stream troughing over the southern Plains this weekend best favors a threat of heavy rainfall and strong convection from Texas to the lower MS Valley as fueled by deepening Gulf of Mexico moisture and instability. The system is expected to shear northeastward into early next week along with a waning rainfall focus across the east-central then eastern U.S. with lead return flow. Upstream, an approaching Pacific trough aloft and leading cold front will start a pronounced cooling trend by the weekend and focus generally modest Pacific Northwest to north-central Rockies precipitation, albeit with a threat of terrain enhanced spring snows. Steady system progression and lead impulse ejections may combine with measured north-central Plains cyclogenesis/frontogenesis and TX dryline formation to favor an emerging pattern for ample Plains convection by early next week that shifts eastward near an increasingly sharp and wavy front from the east-central U.S. to the Northeast. Expect above normal warm sector temperatures for the East and the South. Schichtel Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook 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