Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 239 AM EST Wed Dec 18 2024 Valid 12Z Wed Dec 18 2024 - 12Z Fri Dec 20 2024 ...Clipper system to bring periods of moderate to heavy snow and gusty winds to the northern Plains and Upper Midwest/Great Lakes the next couple of days... ...Showers and storms continue into the day Wednesday for the Ohio/Tennessee Valleys with some locally heavy rainfall and isolated flash flooding possible... ...Well above average temperatures continue for much of the lower 48... Lower elevation/coastal rain and higher elevation snow will linger into the early morning hours Wednesday over the Pacific Northwest and northern Great Basin/Rockies as an upper-level wave departs the region. The wave will then pass over the northern High Plains, leading to lee cyclogenesis and the organization of a clipper system that will drop east-southeastward over the Plains and Midwest the next couple of days. Strengthening moist southerly flow over colder air to the north will bring an intensifying band of snow to the northern Plains Wednesday evening and into the overnight hours. Winter Storm Watches have been issued for northern and eastern North Dakota and northwestern Minnesota where 3-6 inches of snow, locally higher, can be expected. A wintry mix will be possible to the south of the heaviest snow with some snow and light ice accretions possible from eastern Montana southeastward through western North Dakota and into eastern South Dakota. In addition, very strong, gusty winds are expected across the northern Rockies and High Plains Wednesday into Thursday. This will lead to blowing snow and low visibility where snow is either falling or remains on the ground. The system will pass through the Upper Midwest/Great Lakes Thursday, bringing some moderate to locally heavy snowfall, particularly across portions of northern Wisconsin. Showers and thunderstorms continue this morning ahead of a cold front stretching from the Ohio Valley southwest through the Tennessee/Lower Mississippi Valleys and into the southern Plains. Some locally heavy rainfall is expected across the Ohio and Tennessee Valleys where storm motions more parallel to the slow moving front will lead to a few repeated rounds of storms. Isolated flash flooding will be possible particularly across the Tennessee Valley where local soil conditions are more saturated. The boundary will become more progressive by Wednesday afternoon and sweep eastward across the Southeast and to the East Coast into Wednesday evening, with some more isolated storms possible. Moist flow along a warm front lifting northward ahead of the system will also bring moderate rainfall to the coastal Northeast as well as the potential for some accumulating snow for higher elevations of the interior Northeast Wednesday afternoon through the early morning hours Thursday. Precipitation should come to an end for all but Florida by Thursday afternoon as the front pushes into the Atlantic. Elsewhere, thunderstorms remain in the forecast for South Florida Wednesday with some very heavy downpours and isolated flooding possible for urban areas. Extreme to Critical Fire Weather conditions have also been outlined by the Storm Prediction Center in the Los Angeles vicinity as gusty winds and dry conditions remain in place. Precipitation chances will return to the Pacific Northwest by Thursday evening as another Pacific system approaches the region. Much of the lower 48 will continue to see well above average temperatures over the next couple of days, with highs running 10-20 degrees above average for the Southeast Wednesday (60s-70s), the south-central U.S. Thursday (60s-70s), and the West through Thursday (40s-50s interior, 60s-70s West Coast and Deserts). The Northeast will be more seasonable with highs in the mid-30s (interior) to low 50s (coast). One region that will see much colder temperatures will be the Northern Plains/Upper Midwest, where highs will mainly be in the teens and 20s and gusty winds will lead to even colder wind chills. The northern High Plains will see some relief Thursday as downsloping winds bring warmer temperatures. Putnam Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php