Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 257 AM EST Sat Nov 21 2020 Valid 12Z Sat Nov 21 2020 - 12Z Mon Nov 23 2020 ...Rain will develop from the Middle Mississippi Valley to the Ohio Valley/Lower Great Lakes... ...Rain and snow across the Great Lakes into parts of the Northeast... ...Air Stagnation Advisories over parts of Oregon... A front extending from the Northeast southwestward to the Southern Plains will develop a wave of low pressure over the Southern Plains that will move northeastward to the U. S.-Quebec border by Monday. Moisture will pool along the boundary aiding in producing rain with embedded thunderstorms from parts of the Southern Plains/Middle Mississippi Valley into the Ohio Valley on Saturday. On Sunday morning, as the rain expands into parts of the Lower Great Lakes/Northern Mid-Atlantic, snow will develop over parts of the Great Lakes. As the low moves farther northeast, rain will move into parts of the Northeast overnight Sunday. By Monday morning, snow will develop over parts of the Lower Great Lakes as rain extends from New England to the Southern Mid-Atlantic. The snow will aid in producing hazardous driving conditions. Meanwhile, another boundary moving eastward from Central Canada will move into the Upper Midwest producing rain and snow on Sunday. On Sunday afternoon, snow will move into the Upper Great Lakes, merging with the western edge of the eastern system by Monday morning. Additionally, upper-level ridging building over the Northwest and with high pressure at the surface, the air over parts of Oregon will become stagnant. Air Stagnation Advisories have been posted over parts of Oregon Through Sunday morning. On Sunday, multiple fronts will move into the Pacific Northwest. The systems will produce rain over parts of the Northwest on Sunday afternoon. As the precipitation moves inland, higher elevation snow and lower elevation rain will develop over the interior of the Northwest. Furthermore, upper-level energy and weak moisture will aid in producing higher elevation snow and rain over parts of the Central Rockies and the Southern High Plains overnight Sunday. Ziegenfelder Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php