Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 311 AM EST Wed Dec 23 2020 Valid 12Z Wed Dec 23 2020 - 12Z Fri Dec 25 2020 ...High winds and heavy snow are forecast in the north-central U.S. today and tonight, causing blizzard conditions... ...Heavy rain (and thunderstorms in the South) and damaging wind gusts are likely for the East through Christmas Day... A potent surface low pressure system is forecast to move across the Upper Midwest today toward the Upper Great Lakes, spreading snow and high winds to north-central U.S. on its backside. Snow of over 6 inches is possible across northern portions of the Plains and into the Upper Midwest and Upper Great Lakes region through tonight. Heavy snow will then continue for the Upper Peninsula of Michigan and western Lower Michigan on Thursday in favored lake effect areas. Additionally, high winds are likely today given the depth of the surface low. High Wind Warnings and Wind Advisories are in effect for much of the Plains and into the Mississippi Valley region. In the eastern Dakotas, northeastern Nebraska, parts of Minnesota, and northwestern Iowa, Blizzard Warnings are in place where the snow and winds could combine to create blizzard conditions, with lowering visibility and treacherous travel conditions. A strong cold front associated with the low will sweep across the Mississippi Valley today and into the Ohio/Tennessee Valleys early Thursday. Moisture from the Gulf of Mexico is forecast to stream in today ahead of the cold front, leading to increasing rain chances for the Lower Mississippi Valley into the Tennessee Valley through tonight. There is a Slight Risk of severe weather in place from the Storm Prediction Center for the central Gulf Coast as well, where instability will be the highest and could cause strong thunderstorms today and tonight. Then as the front tracks eastward Thursday, heavy rain of 1 to 3 inches is forecast for the eastern third of the country through Christmas morning. Severe thunderstorms are once again possible Thursday, with a Slight Risk of severe weather centered over eastern North Carolina, but the bigger hazard may be flooding and flash flooding. A Slight Risk of excessive rainfall is in place for the Appalachians and into the northern Mid-Atlantic region and Northeast. For many areas, the rain is expected to fall on top of a deep and relatively fresh snowpack from the nor'easter last week, exacerbating flooding concerns as rain could cause rapid snowmelt. Another concern is the added weight that rain could put on top of roofs of buildings that remain covered by heavy snow. Also, winds remain a threat with this low pressure system as it tracks toward the east, and High Wind Watches are already posted for eastern New England. The strong cold front will be a dividing line between much below normal temperatures by 10 to 20 degrees behind the front in the western and then central U.S., with much above normal temperatures ahead of it in the Ohio Valley and Great Lakes region today and across the East Thursday. The warm temperatures (and dewpoints) in the Northeast Thursday should be another contributing factor to flooding there, since it could cause rapid snowmelt into nearby rivers and streams. Also, the cold temperatures will support snow of possibly several inches across eastern portions of the Ohio Valley and across the Central Appalachians Thursday into Christmas morning. Elsewhere, fire danger is a concern across portions of Southern California today and Thursday, where the Storm Prediction Center has outlined a Critical Risk and there are Red Flag Warnings in effect. Dry conditions could cause Elevated Risks of fire weather in the Southern Plains as well. Tate Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php