Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 235 AM EST Mon Dec 16 2024 Valid 12Z Mon Dec 16 2024 - 12Z Wed Dec 18 2024 ...Modest atmospheric river activity to bring unsettled weather to the Northwest, including heavy rains for the coastal ranges and accumulating snow for the higher elevations... ...Wet conditions expected for much of the eastern half of the country the next couple of days... ...Above average temperatures, mild conditions expected for much of the country to start the week... A pair of Pacific systems will help to focus a flow of moisture over the Northwest in an active Atmospheric River pattern the next couple of days. Precipitation continues this morning as moisture flows inland from the first system bringing moderate to heavy coastal rain, an inland wintry mix, and heavy higher elevation mountain snow across the Pacific Northwest, northern California, and the northern Great Basin/Rockies. The heaviest precipitation will be focused southward today across Oregon/northern California and inland through central Idaho into northwest Wyoming. The focus will shift northward on Tuesday bringing heavier rain to coastal Washington state as well as heavy snow to the northern Cascades. Snow totals of 4-8" will be common with locally higher totals over a foot for the highest peaks expected, particularly for the southern Cascades in Oregon Monday. To the east, light to moderate rainfall continues this morning over the Mid-Atlantic with some wintry precipitation over the Interior Northeast, which should taper off through early afternoon. A more focused corridor of showers and thunderstorms will redevelop through the day ahead of a cold front over the Ohio Valley southwestward through the Lower Mississippi Valley/Southern Plains. Some moderate to locally heavy rainfall will be possible, particularly for the Ohio Valley. This system will bring another wave of rain through the Mid-Atlantic Monday evening and New England Tuesday morning, with a wintry mix possible for interior locations. An approaching upper-level wave will help to kick off another round of showers and storms along the frontal boundary from the Ohio Valley southwest through the Southern Plains Tuesday. Elsewhere, an upper-level wave passing over the Northern Plains/Upper Midwest will bring some snow showers on Tuesday with some light accumulations possible. Some lake effect snow showers are also expected to continue downwind of the Great Lakes, particularly Lakes Erie and Ontario. Daily shower and thunderstorm chances are forecast for the Florida Peninsula with coverage and intensity increasing on Tuesday along the Atlantic Coast. Much of the country will see high temperatures above average with generally mild conditions. Some of the greatest anomalies will be over the Midwest Monday as highs climb into the 50s, and over the Northeast Tuesday with highs into the 50s and 60s. Frontal passages will lead to more temperature fluctuation along the northern tier of the country while the southern tier will remain more stable, with daily highs generally in the 60s and 70s. Putnam Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php