Extended Forecast Discussion NWS Weather Prediction Center College Park MD 410 PM EDT Fri Oct 11 2019 Valid 12Z Mon Oct 14 2019 - 12Z Fri Oct 18 2019 ...Pattern Overview and Guidance/Uncertainty Assessment... A deep upper low initially just north of the Great Lakes region Monday will weaken and lift northward across eastern Canada. A progressive shortwave coming out of the Canadian Rockies will sweep into the northern Plains and Upper Midwest Tuesday, pushing a cold front through the region and eventually spawn a low pressure system over the Great Lakes Wednesday. This system will reinforce troughing over the central/eastern US and push a strong cold front well south into portions of Florida by late next week. Across the west, persistent low pressure off British Columbia will bring a parade of cold fronts into the Pacific Northwest, keeping relatively active weather in place for much of the extended forecast period. Average to slightly above average forecast confidence early in the forecast period (Day 3/4 - Mon/Tue) resulted in a preferred blend of primarily global deterministic models. However, by Day 5 through Day 7, forecast confidence drops considerably as the evolution of the upper level pattern across the Pacific Northwest into the northern Plains becomes less certain. The 00Z and 06Z GFS was much faster pushing shortwave energy across the CONUS and closing off over the northern Plains, compared to the rest of the guidance. The ECMWF/CMC/UKMET solutions are slower, holding back energy off the Pacific Northwest coast, and this scenario is preferred at this time. The forecast was leaned heavily on the ECMWF and ECENS/NAEFS means by Day 6-7 given a solution that fit reasonably well within the ensemble consensus. ...Weather Highlights/Threats... A weakening/stalled frontal boundary lingering over the Lower Mississippi Valley to Southeast Mon-Tue will be the focus for widespread showers and thunderstorms. Model consensus suggests that 2-3 inches of rain may be possible across portions of these areas Mon-Tue. As the area of low pressure develops mid-week over the Great Lakes and moves into the Northeast U.S., deeper moisture will be pulled northward and result in widespread rainfall. Some of this could be locally heavy. 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/Taylor 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 Hazards: - Heavy rain across portions of California, the Pacific Northwest, and the Northern Great Basin, Tue-Fri, Oct 15-Oct 18. - Heavy rain across portions of the Lower Mississippi Valley, the Tennessee Valley, the Southern Mid-Atlantic, the Southern Appalachians, the Southeast, and the Southern Plains, Mon-Tue, Oct 14-Oct 15. - Heavy rain across portions of the Northeast, Wed-Thu, Oct 16-Oct 17. - Flooding possible across portions of the Southeast, the Upper/Middle Mississippi Valley, the Great Lakes, and the Northern Plains. - Flooding occurring or imminent across portions of the Northern/Central Plains, the Upper/Middle Mississippi Valley, and the Great Lakes. - Flooding likely across portions of the Middle/Lower Mississippi Valley, and the Southern Plains. - Much below normal temperatures across portions of the Northern/Central Plains, and the Upper Mississippi Valley, Mon-Wed, Oct 14-Oct 16. - High significant wave heights for coastal portions of the Pacific Northwest, Thu-Fri, Oct 17-Oct 18. 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