US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 336 PM EST Wed Dec 12 2018 Valid Saturday December 15 2018 - Wednesday December 19 2018 Hazards: Heavy precipitation across portions of California, the Central Great Basin, the Pacific Northwest, and the Northern Great Basin, Sat-Wed, Dec 15-Dec 19. Flooding possible across portions of the Southeast and the Mid-Atlantic. Flooding occurring or imminent across portions of the Southeast, the Mid-Atlantic, and the Southern Plains. Flooding likely across portions of the Southeast. High winds across portions of California, the Pacific Northwest, and the Northern Great Basin, Mon-Wed, Dec 17-Dec 19. Much above normal temperatures across portions of the Upper Mississippi Valley, the Northern Plains, and the Northern Rockies, Sat-Wed, Dec 15-Dec 19. High significant wave heights for coastal portions of California and the Pacific Northwest, Sat-Wed, Dec 15-Dec 19. High winds across portions of mainland Alaska and the Aleutians, Mon-Tue, Dec 17-Dec 18. High winds across portions of the Alaska Panhandle, Sat, Dec 15. High significant wave heights for coastal portions of the Alaska Panhandle and mainland Alaska, Sat-Sun, Dec 15-Dec 16. Detailed Summary: The Pacific Northwest into Northern California is expected to be the most impacted area in the medium range hazards period. A series of upper level systems will move onshore providing a constant inflow of moisture into the region and periods of organized moderate to locally heavy precipitation through much of the period. Expect rainfall for the coastal and lower elevations, and heavy snow in the mountains. Models show 5-day totals of multiple inches of rainfall possible along the coast and snow measured in feet in the highest terrain, particularly in the Washington Cascades. High winds are also expected across parts of the Pacific Northwest with significant waves along the coast and near offshore waters. With heavy rainfall expected in the short range period, flooding may be an ongoing concern across parts of the Southern Plains to the Southeast and lower Mid-Atlantic especially in places like North Carolina who have recently seen significant snowfall. The most significant temperature anomalies are expected across the northern tier with a much above normal temperature area highlighted across the northern High Plains and Plains. Normally in the winter time, this would not necessarily be a hazard, but given daytime temperatures 10 to 20 degrees above normal (lending to above freezing values) and overnight lows expected to be below freezing, there is concern for melting and refreezing of surfaces. Multiple cyclones progressing south of the Aleutians and into the Gulf of Alaska will provide coastal locations across the Aleutians, southern coast, and the Panhandle with rounds of significant waves, high winds, potentially heavy rainfall. Model uncertainty remains with how much rain may fall and how widespread so a hazard was not indicated on the day 3-7 threats chart but the potential is certainly there for at least locally heavy rainfall. Santorelli