Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Thu Nov 07 2019 Valid 12Z Sun Nov 10 2019 - 12Z Thu Nov 14 2019 ...Rockies to East Arctic Outbreak Includes a Heavy Snow/Ice Threat... ...Pattern Overview and Guidance/Predictability Assessment... The larger scale flow pattern is expected to reamplify next week with a U.S. West Coast to Alaska ridge and downstream trough over the central/eastern CONUS. The latest GFS/ECMWF and GEFS/ECMWF ensemble mean solutions now cluster fairly well for much of the medium range period, bolstering larger scale flow evolution confidence. ...Weather Highlights/Threats... Arctic-sourced high pressure and lead cold front will surge south from Canada to produce much colder than normal temperatures over the eastern 3/4 of the lower 48 states this weekend into next week. The surface high pressure center will tracks from the Canadian Prairies southeastward to the eastern U.S. next week. Expect a broad coverage of maximum temperatures 15-25F below normal and a risk of widespread record cold temperatures will spread across the central and eastern U.S. A lead weekend clipper system and trailing cold cyclonic flow will bring mostly snow to the Great Lakes/Northeast with snows prolonged into next week by lake effect. Meanwhile, locations along the eastern slopes of the northern-central Rockies will see periods of enhanced snows as the trailing Arctic front digs southward resulting in upslope flow. Organized waves of low pressure along the front are expected to track along a profound baroclinic zone from the southern Plains to off the East Coast Mon-Wed. These will produce a swath of moderate rainfall along/south of the boundary from across the South and Southeast/Mid-Atlantic, but also a threat of snow/ice north of the front in the cold air from the s-central Plains northeastward from the Mid-South to the OH Valley/Appalachians/Mid-Atlantic/Northeast. Snows may be additionally enhanced over the Northeast by coastal storm development, although there remains uncertainty with coastal proximity and full extent of wintry onshore impacts. This risk is depicted in the WPC Winter Weather Outlook probabilities. There is guidance variance with respect to the handling of upstream trough energy/heights falls to work through western Canada and the Northwest U.S. Tue-Thu through an ambient mean upper ridge. A composite suggests the systems offer modest precipitation potential focusing over favored terrain of the Northwest to snowy Rockies. 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