Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 333 PM EST Wed Dec 20 2017 Valid 00Z Thu Dec 21 2017 - 00Z Sat Dec 23 2017 ...Heavy snow over parts of the Central Rockies... ...Snow possible from parts of the Northern Plains across the Great Lakes into the Northeast... ...Heavy rain possible over parts of the Lower Mississippi Valley/Tennessee Valley... Strong storm over Great Basin/Central Plains will lift northeastward to the Ohio Valley by Friday. The system will produce coastal rain and higher elevation snow over parts of the Pacific Northwest with snow over parts of the Northern Intermountain Region/Northern Rockies and the Great Basin. The rain and snow will come to an end over the Pacific Northwest/Northern Intermountain Region overnight Wednesday. In addition, snow over the Northern Plains will spread into the Upper Great Lakes also overnight Wednesday as snow moves into the Central Rockies ending overnight Thursday. On Thursday, snow and some rain will develop over parts of the Northern/Central Plains into the Upper Great Lakes. The snow will also end over Central Plains/Upper Mississippi Valley overnight Thursday, too. Overnight Thursday, snow will move into the Northeast while rain moves into parts of the Ohio Valley and parts of the Northern Mid-Atlantic by Friday morning. The associated warm front will be dammed against the Appalachians Thursday afternoon into Friday. With the damming, there is a risk of rain/freezing rain developing over parts of the Lower Great Lakes/Northern Appalachians also overnight Thursday into Friday. Additionally, as the associated cold front moves from the Plains into parts of the Mississippi Valley, moisture from the Gulf of Mexico will flow northeastward over the Southern Plains into the Lower Mississippi/Tennessee Valleys on Thursday afternoon into Friday. Likewise, overnight Thursday into Friday, showers and thunderstorms will develop over parts of the Southern Plains into the Lower Mississippi/Tennessee Valleys. Meanwhile, upper-level energy over the Southern Appalachians/Southeast will move eastward out over the Western Atlantic Wednesday evening into Thursday morning. The system will produce rain and thunderstorms over parts of the Southern Ohio Valley, Tennessee Valley, Southern Mid-Atlantic, Southeast and Eastern Gulf Coast that will move eastward off the Southeast Coast by Thursday morning into afternoon. Elsewhere, a front will move southward from Western Canada into the Northern Plains to the Pacific Northwest overnight Thursday into Friday. Light snow will develop over parts of the Northern Plains to the Northern Intermountain Region Thursday evening into Friday. Ziegenfelder Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php