Extended Forecast Discussion NWS Weather Prediction Center College Park MD 242 AM EDT Fri Oct 11 2019 Valid 12Z Mon Oct 14 2019 - 12Z Fri Oct 18 2019 ...Pattern Overview and Guidance/Uncertainty Assessment... A relatively amplified and progressive pattern will be in place across the CONUS during the extended period. A deep upper-level low initially in place just north of the Great Lakes on Mon is forecast to lift northward across eastern Canada while a cold front sweeps across the Mid-Atlantic/Northeast. Meanwhile, shortwave energy crossing the Great Basin/Rockies on Mon and the central U.S. on Tue is forecast to amplify across the Great Lakes and eastern U.S. Wed/Thu, moving a relatively strong cold front off the Eastern Seaboard. The pattern will become much more unsettled across the Northwest by the middle of next week as a series of shortwaves/frontal systems approach the region in rapid succession. The WPC medium range forecast was based initially on a multi-model deterministic blend (including the 12Z ECMWF/UKMET/18Z GFS) on days 3-4 (Mon-Tue). Starting on day 5 (Wed), the GFS was removed from the blend, as it become significantly faster than the model/ensemble consensus to lower heights across the Pacific Northwest and farther inland. The differences only increased later in the period, with the GFS developing a deep closed upper-level low across the north central U.S. by days 6-7 (Thu-Fri), while the ECMWF along with most ECENS and CMCE ensemble members keep broad anticyclonic flow across the central U.S., and more amplified troughing along the West Coast. Thus, the forecast during days 5-7 showed gradually increasing weight on the ECENS/NAEFS ensemble means, with some continued weight on the ECMWF through the end of the forecast period given a solution that fit reasonably well within the ensemble consensus. ...Weather Highlights/Threats... A weakening frontal boundary forecast to linger from the lower Mississippi Valley to the Southeast days 3-4 is expected to produce widespread showers and thunderstorms, with heavy rain possible. Model consensus suggests that 2-3 inches of rain may be possible across portions of these areas Mon-Tue. Farther north, low pressure expected to move from the mid-Mississippi Valley on Tue to the Ohio Valley/Northeast Wed/Thu is expected to gradually draw in deeper moisture, and widespread moderate to locally heavy rain is forecast across the Northeast Wed into Thu. Meanwhile, precipitation is expected to gradually increase across the Pacific Northwest starting next Tue and continuing through the end of the week as multiple shortwaves/frontal systems affect the region. Snow-levels are forecast to be relatively high initially, but should begin to fall by later in the week as lower heights begin to press inland. Regardless, heavy precipitation is expected to become widespread across the coastal ranges of the Northwest as well as the Cascades by later in the week, with multi-inch liquid equivalents possible. Temperatures are forecast to initially be well below average across the north central U.S. in the wake of this weekend's winter storm. Highs are forecast to be 15-25 deg F below average across portions of the northern Plains and Upper Midwest Mon-Wed, before temperatures moderate later in the week. Cooler temperatures are forecast to spread into the eastern half of the nation by the middle to end of next week as Canadian high pressure overspreads the region behind the cold front. High temperatures 5 to 15 deg below average are forecast across a large area from the Mississippi River to the Eastern Seaboard. Ryan 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