Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Fri Aug 24 2018 Valid 12Z Mon Aug 27 2018 - 12Z Fri Aug 31 2018 ...Pattern Overview and Weather Highlights/Hazards... Amplified mid-upper level troughing over the north-central Rockies and Intermountain West Monday will trek enewd over the n-central U.S. then eastern Canada/Northeast Tuesday-Thursday. This will support a wavy/cooling frontal system underneath to focus lingering periods of organized convection expected to be heaviest from the mid Mississippi Valley and Midwest/Great Lakes onward, but also working with less predictable impulse support farther south into deepened mositure and instability within a summer time hot sector. Some of these convective downpours will produce local runoff issues with repeat/training of cells. Upstream, a strong upper high south of the Gulf of Alaska will retrograde and allow cooling trough position reinforcement into/offshore the Pacific Northwest mid-late next week with enough flow to initiate some precipitation. ...Guidance Evaluation/Preferences... Models and ensembles show a similar larger scale pattern in the 3-5 day period, but differences are problematic with smaller scale impulses and lower atmospheric focus to drive convection. Addressed this with a blend of the GFS/ECMWF, GFS/ECMWF ensembles and WPC continuity. Forecast spread increases enough into days 6/7 to rely mainly on GEFS/ECMWF ensembles and statistical/bias corrected guidance. Systems moving to the eastern Pacific and lower 48 in this pattern may favor the ampified side of the solution envelope due to downstream ripple effects from the entrainment of extratropical lows associated with current west Pacific tropical systems Cimaron and Soulik toward Alaska. 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