Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 252 AM EST Thu Dec 16 2021 Valid 12Z Thu Dec 16 2021 - 12Z Sat Dec 18 2021 ...There is a Marginal Risk of excessive rainfall over parts of the Ohio, Tennessee, and Lower Mississippi Valleys through Friday morning... ...There is a Slight Risk of excessive rainfall over parts of the Ohio, Tennessee, Middle/Lower Mississippi Valleys, and Southern Plains on Friday into Saturday morning... ...Heavy snow over the Sierra Nevada Mountains will wind down on Thursday; Chance of freezing rain over parts of the Upper Midwest and Northern New England early on Thursday... ...Temperatures will be 20 to 30 degrees above average for the Lower Mississippi Valley, Great Lakes/Ohio Valley, into the Northeast... An area of deep low pressure over Central Ontario will produce high winds over the Upper Midwest into the Great Lakes. Therefore, High Wind Warnings are issued over the region, with Storm Warnings over Lakes Michigan, Superior, and parts of Lake Huron. Light snow and rain will develop over parts of the Upper Mississippi Valley and Upper Great Lakes, with isolated pockets of rain/freezing rain along the rain-snow line. The rain will change over to all snow on Thursday afternoon, ending overnight Thursday with light lake effect snow downwind from Lake Superior on Friday. Furthermore, rain in the Great Lakes will move into the Northeast, with light snow developing over parts of Northern New England. As warm air moves over the region, cold air will get trapped in the valleys and produce areas of freezing rain over parts of Northern New England through Thursday evening. The Associated strong cold front extending from the Great Lakes southwestward to the Southern Plains will move eastward off the Northeast and Mid-Atlantic Coast by Friday afternoon. Showers and thunderstorms will develop along and ahead of the front from the Ohio Western Valley to the Southern Plains. The risk of severe thunderstorms is marginal. However, the associated heavy rain will impact the area. Therefore, the WPC has issued a Marginal Risk of excessive rainfall over parts of the Ohio, Tennessee, and Lower Mississippi Valleys through Friday morning. The associated heavy rain will create localized areas of flash flooding, affecting areas that experience rapid runoff with heavy rain. As moisture pools along the boundary, the risk of excessive rainfall increases on Friday. Therefore, the WPC has issued a Slight Risk of excessive rainfall with these thunderstorms over the Ohio, Tennessee, Middle/Lower Mississippi Valleys, and Southern Plains on Friday into Saturday morning. The associated heavy rain will create mainly localized areas of flash flooding, with urban areas, roads, and small streams the most vulnerable. Moreover, ahead of the front, temperatures will be 20 to 30 degrees above average for the Lower Mississippi Valley, Great Lakes/Ohio Valley, into the Northeast. In addition, many record-high temperatures are forecast over parts of the Ohio Valley into the Northeast. In the meantime, a front onshore over the Northwest will move southward over the West Coast and dissipate by Thursday evening, as the associated upper-level energy moves inland to the Rockies by Friday and to the Upper Midwest by Saturday. The system will produce coastal rain and higher elevation snow over the Pacific Northwest and Northern/Central California. Rain will move into parts of Southern California by Thursday evening. The rain and snow wind down overnight Thursday over the Pacific Northwest and California. Concurrently, snow will move into parts of the Northern/Central Rockies and the Northern High plains by Friday morning and into the Northern Plains/Upper Mississippi Valley overnight Friday. Meanwhile, a wave of low pressure will develop over parts of the Central Plains/Middle Mississippi Valley by Friday evening. The low moves into the Western Ohio Valley by Saturday morning. The system will produce light snow over parts of the Great Lakes and rain from the Ohio Valley into the Mid-Atlantic by Saturday morning. Ziegenfelder Graphics are available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php