Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1247 PM EDT Wed Jul 08 2020 Valid 12Z Sat Jul 11 2020 - 12Z Wed Jul 15 2020 1645 UTC Update... Overall, changes to the ongoing WPC medium range forecast during this update were relatively minor. Updated to incorporate some of the latest model/ensemble guidance, but continued similar to overnight with a blend of the 00Z ECMWF and the 00Z/06Z ECENS/GEFS ensemble means, respectively. The GFS remained more progressive than consensus with the low along the Eastern Seaboard, while the UKMET remained a bit deeper than consensus. Elsewhere, models/ensembles continued to show relatively agreeable features at the larger scales across the CONUS through the medium range forecast period. Ryan Previous Discussion (issued at 0535 UTC)... ...Guidance/Predictability Assessment... Model differences remain with an Eastern Seaboard coastal low whose potential development is being monitored by NHC. The last few GFS runs, including the 00 UTC run, have been the most progressive with this low into New England into the weekend. Recent UKMET runs, including the 00 UTC run, have been the most developed (likely benefiting from a more offshore track over warmed waters). The WPC blend leans closer to the 12 UTC ECMWF that fits better within the overall ensemble spread and WPC continuity. For the rest of the CONUS, there is above average consensus for troughing over the Northwest and the East to sandwich an amplified Southwest/south-central U.S. ridge days 3-7. An ECMWF and GEFS/ECMWF ensemble means blend seems to provides the best forecast starting point and continuity. ...Weather Pattern/Hazard Highlights... Ample upper trough energies will work inland over an unsettled Northwestern U.S. and western Canada. Height falls/ejecting impulses progress downstream over southern Canada and the U.S. northern tier. This forces moderating fronts over the broad region and some strong to severe thunderstorms. Convective rainfall potential may focus from the Midwest to the Southeast/East. Meanwhile, triple digits maximum temperatures to approach or exceed heat records are likely from portions of CA and the Southwest/southern Great Basin to the south-central Plains. Heat indices will make it feel closer to 115 degrees in some places. A local heavy rain/weather/maritime threat is expected to lift from the coastal Mid-Atlantic to New England Saturday, as contingent upon potential coastal low development and track. 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