Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 218 PM EST Thu Dec 12 2024 Valid 00Z Fri Dec 13 2024 - 00Z Sun Dec 15 2024 ...Moderate to heavy lake-effect snow downwind from Lake Ontario on Friday; light to moderate lake-effect snow downwind from most of the Great Lakes Thursday evening into Friday... ...Moderate to heavy snow over parts of the Sierra Nevada Mountains and the Northern Intermountain Region on Friday evening into Saturday; 0.10 inches of rain/freezing rain over parts of the Middle Mississippi Valley on Friday evening into Saturday... ...Temperatures will be 10 to 20 degrees below average over parts of the Upper Midwest... A front over parts of the Southwest/Southern California will move eastward to the Middle/Lower Mississippi Valley and Southern Plains by Saturday. Moisture associated with the system will produce coastal rain and higher-elevation snow over parts of the Pacific Northwest and Northern California on Thursday afternoon. Overnight Thursday, the rain and higher-elevation snow will move into Central California. The rain and higher-elevation snow will continue into Saturday over parts of the Northwest and California. On Friday, another front over the Eastern Pacific will move onshore over parts of the Northwest and California and move inland as far eastward as the Northern Intermountain Region by Saturday. The storm will produce more coastal rain and higher-elevation snow over parts of the Pacific Northwest and Northern California. Additional moisture will move onshore Friday evening, producing moderate to heavy snow over parts of the Sierra Nevada Mountains and the Northern Intermountain Region through Saturday. Meanwhile, on Friday into Saturday, as the lead front moves into the Middle/Lower Mississippi Valley and Southern Plains, return flow off the Gulf of Mexico will start to stream northward over parts of the Southern Plains, producing showers and thunderstorms. The showers and thunderstorms will expand north and eastward into the Middle/Lower Mississippi Valley on Saturday. In addition, rain will move into the Ohio and Tennessee Valleys on Saturday. Additionally, overnight Friday, as the moisture streams farther northward over the Mississippi Valley, rain/freezing rain will develop over parts of the Middle Mississippi Valley. Slightly farther north, light snow will develop over parts of the Upper Mississippi Valley on Saturday. Furthermore, on Thursday evening, cold high pressure over the Upper Mississippi Valley will move eastward to the Northeast by Saturday. Moreover, cold air associated with the high will bring temperatures 10 to 20 degrees below average over parts of the Upper Midwest. Upper-level energy moving over the Great Lakes will produce light to moderate lake-effect snow downwind from most of the Great Lakes Thursday evening into Friday. However, moderate to heavy lake-effect snow will develop downwind from Lake Ontario on Thursday evening into Friday. By Saturday, most of the lake-effect snow will wane. Elsewhere, easterly flow off the Atlantic will produce light rain over parts of Florida s east coast, starting on Friday into Saturday. Ziegenfelder Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php