Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EST Sun Dec 08 2024 Valid 12Z Sun Dec 08 2024 - 12Z Tue Dec 10 2024 ...Heavy rain threat emerges across the Deep South late Sunday into Monday... ...Periods of mixed rain and snow linger from the Great Lakes to northern New England through Monday night... ...Unsettled and windy weather spreading across the Pacific Northwest this weekend will reach into the northern Plains as snow/wintry mix by Monday... ...Well above average temperatures will overspread the central and eastern U.S. as cold air surges into the western U.S.... A major reversal of the weather pattern is forecast to occur across mainland U.S. during the next couple of days. The remaining cold air across the eastern U.S. originated from the recent arctic outbreak will be dispelled by an eastward expanding mild air mass from the central U.S. Meanwhile, the mild air across the western U.S. in recent days will be dispelled by a surge of cold air currently advancing through the northwestern U.S. The upper-level trough responsible for this cold surge into the western U.S. will first spread mixed rain and snow through the northern Rockies today behind a cold front along with windy conditions. Daytime heating will keep the precipitation mainly in the form of rain as it moves quickly across the northern Plains today. By tonight, colder air from Canada is forecast to filter south from Canada behind a low pressure system. This will bring periods of snow into the northern Plains and areas farther west to the foothills of the northern Rockies through tonight and into Monday, along with windy conditions. The higher elevations will receive higher amounts of snow, with the highest snowfall likely near the northern slopes of the Black Hills where more than a foot of new snow is possible. Portions of the central Rockies into the Front Range of Colorado and down into northeastern New Mexico can expect to receive a period of snow from this system through Monday night into Tuesday morning. Ahead of the cold front trailing south from the aforementioned low pressure system, a jet stream sliding across northern Mexico will interact with a coastal front and a low pressure wave near the western Gulf Coast to bring an increasing threat of heavy rain farther inland across the lower Mississippi Valley and then into the Deep South through the next couple of days. Warmer and more unstable air arriving from the Gulf will help trigger heavier showers and thunderstorms for the eastern portion of these areas. The overlapping elements coupled with some recent rainfall will result in the possibility of scattered instances of flash flooding. The Weather Prediction Center maintains a Marginal Risk of Excessive Rainfall across the central Gulf Coast region for Monday into early Tuesday, with a Sight Risk area from southeastern Louisiana to southern Mississippi. Across New England, widespread snowfall is in progress today ahead of a clipper system moving quickly eastward along a warm front lifting north across the region. Widespread snowfall of up to 6 inches can be expected from the Adirondacks eastward through Maine before the snow tapers off tonight. More snow will then skirt the upper Great Lakes ahead of the warm front associated with the northern Plains low pressure system, with 6-8 inches expected over the Upper Peninsula of Michigan and the Arrowhead of Minnesota. A period of rain will sweep across the Ohio Valley Sunday night, then the Appalachians and the northern Mid-Atlantic on Monday ahead of the trailing front, followed by the next round of snow across northern New England Monday night. Mild Atlantic air will keep the precipitation as rain for southern New England into Tuesday morning. Kong Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php