Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 327 PM EST Mon Dec 18 2017 Valid 00Z Tue Dec 19 2017 - 00Z Thu Dec 21 2017 ...Heavy snow possible over the Cascades and Northern Rockies... ...Heavy rain possible over parts of the Pacific Northwest Coast... ...Heavy rain possible over portions of the Southern Plains into the Southern Appalachians... Onshore flow ahead of the next system will aid in producing rain and highest elevation snow over parts of the Pacific Northwest and snow and lower elevations rain over parts of the Northern Intermountain Region/Northern Rockies through Tuesday morning. On Tuesday the next system will begin to move onshore over the Pacific Northwest moving inland to the Northern Rockies/Great Basin and parts of Central California by Wednesday. The snow levels will decrease over the Northwest as the associated front moves inland, lowering to the coast over parts of Northwestern Washington State. Rain and higher elevations snow will develop over the Northwest and snow over the Northern Intermountain Region/Northern Rockies on Tuesday. Rain and higher elevation snow begins to move into Northern California by Tuesday evening that will expand into Central California and snow in the Great Basin overnight Tuesday into Wednesday. In addition, snow will begin to develop over parts of the Northern Plains also overnight Tuesday into Wednesday. Meanwhile, an upper-level low over Northwestern Mexico will move northeastward to the Lower Mississippi Valley by Wednesday while weakening. Moisture from the Western Gulf of Mexico will stream northward over the Southern Plains into parts of the Lower Mississippi Valley and into the Southeast by Wednesday morning. The moisture and upper-level energy will aid in producing showers and thunderstorms over parts of the Western Gulf Coast/Southern Plains that will begin to expand eastward into the Lower Mississippi Valley by Tuesday morning. On Tuesday, the showers and thunderstorms will continue to expand eastward into parts of the Tennessee Valley/Southeast well into Wednesday morning. More to Follow Ziegenfelder Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php