Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 405 AM EDT Fri Sep 29 2023 Valid 12Z Fri Sep 29 2023 - 12Z Sun Oct 01 2023 ...There is a Moderate Risk of excessive rainfall over parts of the northern Mid-Atlantic/Southern New England... ...Moderate snow over parts of the Sierra Nevada Mountains above 9000ft on Saturday... ...Temperatures will be 10 to 20 degrees below average over parts of California, the Great Basin, and the Pacific Northwest on Saturday... On Friday, low pressure along the Mid-Atlantic Coast will slowly move northward to just south of Long Island, New York, then push eastward out over the Western Atlantic by Sunday. The low will pull moist air off the Atlantic, producing areas of heavy rain over parts of northeastern New Jersey, extreme southeastern New York State/Long Island, and Connecticut. Therefore, the WPC has issued a Moderate Risk of excessive rainfall over parts of northern Mid-Atlantic and Southern New England. The associated heavy rain will create numerous areas of flash flooding. Furthermore, many streams may flood, potentially affecting larger rivers. In addition, upper-level energy associated with the low will produce scattered rain over parts of the Mid-Atlantic and the Northeast on Friday and Saturday. Meanwhile, tropical moisture over Florida and upper-level energy will create showers and thunderstorms over parts of Florida through Sunday morning. Additionally, a weak front over parts of the Northern Plains/Upper Mississippi Valley will move into the Upper Great Lakes and dissipate by Friday evening. The system will produce showers and thunderstorms over parts of the Upper Midwest through Sunday. Furthermore, upper-level energy over the North Pacific will move southeastward over California, creating an upper-level low by Saturday evening. Rain will develop over parts of the Pacific Northwest early on Friday morning. Overnight Friday, the rain will move into California and parts of the Great Basin. As the upper-level trough deepens, snow levels will drop over parts of the Sierra Nevada Mountains. On Saturday, the rain moves into parts of Southern California while at elevations above 9000ft, moderate snow will develop over the Sierra Nevada Mountains with rain at lower elevations. The precipitation will continue through Sunday morning. Moreover, the upper-level troughing will allow temperatures to be 10 to 20 degrees below average over parts of California, the Great Basin, and the Pacific Northwest on Saturday. As the deep trough develops over the country's western half, moisture from the Gulf of Mexico will move northwestward over the Southern High Plains. The moisture and upper-level energy will aid in creating showers and thunderstorms over parts of the Southern Rockies/Southern High Plains overnight Friday. On Saturday night, showers and thunderstorms will develop over parts of the Southern High Plains into parts of the Central High Plains. Ziegenfelder Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php