US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 400 PM EST Fri Dec 06 2019 Valid Monday December 09 2019 - Friday December 13 2019 Hazards: - Heavy precipitation across portions of the Pacific Northwest and the Northern Great Basin, Wed-Fri, Dec 11-Dec 13. - Heavy rain across portions of northwestern Washington, Wed-Thu, Dec 11-Dec 12. - Heavy rain from the upper Texas coast to central Louisiana, Fri, Dec 13. - Heavy rain from the northern Mid-Atlantic through the eastern half of New England, and from the Tennessee Valley and the southern Appalachians up along the western slopes of the central Appalachians, Mon-Tue, Dec 9-Dec 10. - Heavy snow across portions of the northern Rockies and the northern Intermountain region, Thu-Fri, Dec 12-Dec 13. - Heavy snow from northern Wisconsin eastward into the central Great Lakes, Mon, Dec 9; and for the central Great Lakes, Wed, Dec 11. - Flooding occurring or imminent across portions of the Northern Plains. - Much below normal temperatures across portions of the Great Lakes, the upper Midwest, and much of the northern Plains, Mon-Wed, Dec 9-Dec 11. - Much below normal temperatures for northern New England, Wed-Thu, Dec 11-Dec 12. - Heavy precipitation across portions of southern Alaska, Mon, Dec 9, and Thu, Dec 12. - High significant wave heights for coastal portions of southern Alaska, Mon, Dec 9. Detailed Summary: A low pressure system should be moving across the upper Midwest into the Great Lakes to start off the Day 3-7 period (Dec 9-13). A swath of wintry precipitation is expected to the north and northwest of the storm track. The ECMWF and the GFS have come into better agreement regarding the timing and intensity of this system. The forecast precipitation axis continues to exhibit notable but reasonable run-to-run variability given the forecast lead time. There appears to be a trend toward lighter precipitation amounts within this axis. A consensus approach continues to put northern Wisconsin and the central Great Lakes areas to be under the highest chance of seeing moderate to heavy snow on Monday. There could be a lull in snow activities over the central Great Lakes on Tuesday but the late-effect snows could become more active on Wednesday as an upper-level disturbance is forecast to move across the region. Behind the low pressure system, models are unanimous on bringing an arctic air mass down from central Canada. Sub-zero temperatures are forecast for the northern Plains to the upper Midwest Tuesday and Wednesday. The much colder than normal temperatures are forecast to spread not too far toward the south and east into central Great Lakes on Wednesday. By next Thursday, the arctic air is expected to reach northern New England. This should be followed by a gradual warming trend for the eastern U.S. as the arctic high pressure system begins to slide off the coast. Ahead of the low pressure system, mild air will overspread much the eastern U.S. Monday and Tuesday. Rainfall amounts of 1 to 2 inches are forecast for the interior portion of the Southeast, including the western slopes of the central and southern Appalachians on Monday and Tuesday associated with a strong cold front. Similar rainfall amounts are also forecast from the northern Mid-Atlantic to coastal Maine during this period where a heavy rain area is indicated. The rain will possibly end as a period of snow from the central Appalachians through the Mid-Atlantic into southern New England Tuesday night. Over the Pacific Northwest, moisture ahead of the next frontal system will likely spread heavy rain into the Olympic Peninsula and heavy snow/rain across much of the Washington Cascades from next Wednesday through Friday. The moisture will then spread further downstream across the Intermountain region and the northern Rockies on Thursday into Friday. In Alaska, a highly amplified synoptic pattern will bring moisture all the way up from the sub-tropics toward southern Alaska early next week. Very heavy precipitation together with winds occasionally reaching storm-force are expected to impact the southern coast of Alaska into the mountainous areas just inland ahead of a low pressure center tracking up a sharp front. The main threat will be across the Chugach mountains, Kenai Peninsula and Alaska range this weekend into early next week, with heavy snow across higher elevations and rainfall of potentially several inches per day at lower elevations. Another significant low pressure system will likely approach the eastern Aleutians with increasing winds and rain by the middle of next week. Uncertainty is bit too high to specify hazard areas for the eastern Aleutians at this time. Kong