Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1109 AM EDT Sat Aug 25 2018 Valid 12Z Tue Aug 28 2018 - 12Z Sat Sep 01 2018 ...Overview and Guidance Evaluation/Preferences... Latest guidance shows a similar larger scale pattern next week as upper ridging holds over the Southeast with successive positively tilted troughs into the Northwest. Upstream ex-tropical systems Soulik and Cimaron will likely amplify the flow into then east of the Bering Sea (see PMDAK) atop a North Pacific upper high which will allow troughing to remain favored in the west. The models/ensembles have wavered on the speed of exiting strung out vorticity features from the mean trough position but given some oscillating variance between model cycles, a blend of the best-clustered solutions was prudent -- this included the 00Z FV3-GFS/ECMWF/Canadian and the 00Z GEFS/ECENS means. Uncertainty expands, as expected, by days 6-7 in the east with the southward extent of the front and areas of convection along/ahead of it back through the central U.S. ...Weather Highlights/Hazards... A wavy frontal system across roughly the northern half of the lower 48 will focus periods of organized convection along in a quite summery air mass, especially east of the Plains. Potentially strong activity should occur from the Plains and Midwest/Great Lakes eastward Tue-Wed ahead of the cold front, though location predictability remains low per SPC. To the south, less predictable mesoscale processes within the hot/humid summertime airmass (temperatures well above average to near record levels, especially for minimums) and deep moisture/instability will also give rise to locally heavy rainfall which may produce local runoff issues with repeat/training of cells. Upstream, a strong upper high south of the Gulf of Alaska will retrograde westward and allow another cooling trough into the Pacific Northwest mid-late week with enough onshore flow to initiate modest precipitation. Fracasso/Schichtel WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found 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