Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EST Mon Dec 16 2024 Valid 00Z Tue Dec 17 2024 - 00Z Thu Dec 19 2024 ...Atmospheric river to bring unsettled weather to the Northwest, including heavy rains for the coastal ranges and accumulating snow for the higher elevations of the Cascades... ...Above average temperatures expected for much of the lower 48 into mid-week... The pattern will remain active across the northwestern U.S., especially the Pacific Northwest, as a strong atmospheric river takes aim across Washington and Oregon for Tuesday. Low level onshore flow will remain across the Pacific Northwest as the latest in a series of upper level troughs moves inland tonight while weakening, followed by stronger but quick moving system for Tuesday afternoon/evening. Showers will transition to steady rain tomorrow with areas of heavy rain becoming likely late Tuesday morning into the evening ahead of a warm front. As a cold front nears the coast late Tuesday afternoon/evening, heavy rain is likely for the Coastal Ranges of northern Oregon into Washington along with the Cascades. While light to moderate snow is anticipated for portions of the Cascade Range through Tuesday morning, snow levels will rise to 7000-8000 ft above sea level for the Washington Cascades during the height of the atmospheric river event late Tuesday with accumulating snow changing to locally heavy rain. The heaviest rain is expected into the Olympics where 2-day rainfall totals of 5 to 7+ inches are expected through Wednesday morning. Elsewhere across the country, the weather will be relatively quiet. A pair of cold fronts moving eastward from the Great Plains/Midwest over the next few days will maintain wet and unsettled weather from the lower/middle Mississippi Valley to the East Coast. Across Florida, locally heavy rain will be possible along the east coast of the Peninsula on Tuesday with an easterly low level flow regime in place, tapping into anomalous moisture over the Caribbean. Rain will linger into Wednesday across Florida. Temperatures for many in the lower 48 will run 10-20 degrees above mid-December averages with the exception of the north-central U.S. Temperatures from eastern Montana to the upper Mississippi Valley will likely be 5 to 15 degrees below average and carry light snowfall accumulations for portions of the region. Otto Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php