Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 352 PM EDT Thu Oct 29 2015 Valid 00Z Fri Oct 30 2015 - 00Z Sun Nov 01 2015 ...Flash flooding possible on Friday across portions of the southern plains... ...Flash flooding possible on Saturday across portions of the lower Mississippi valley... ...Heavy rainfall expected for the Pacific Northwest ... An upper-level trough will move across the southwestern U.S. tonight into Friday, before moving into the central U.S. Friday night into Saturday. A surface low pressure system will develop on Friday across Texas, which will move eastward toward the lower Mississippi valley on Saturday. Abundant moisture from the Gulf of Mexico will begin to stream northward across Texas tonight ahead of the low pressure system. As the moisture interacts with the surface frontal system and the upper-level trough, numerous showers and thunderstorms are expected to develop across portions of the southern plains starting tonight and expanding in coverage on Friday. Showers and thunderstorms are ongoing this afternoon across the southwestern U.S. and these will continue into Friday as well across portions of New Mexico and Colorado, with snow falling at the higher elevations of Colorado. On Saturday the low pressure system and the plume of deep moisture will shift east toward the Gulf Coast and lower Mississippi valley. Heavy rainfall amounts of 2 to 4 inches are expected across portions of the southern plains and lower Mississippi valley. These heavy rainfall amounts will lead to the possibility of flash flooding for portions of the southern plains on Friday and portions of the lower Mississippi valley on Saturday. Widespread rain is also expected farther north late Friday into Saturday, from the central/northern plains to the Great Lakes -- although rainfall amounts will be lighter in these areas. A series of Pacific frontal systems, and a rather constant plume of moisture will affect the Pacific Northwest starting tonight and persisting into Saturday. Heavy rainfall is possible, and rainfall amounts will vary based on elevations. Rainfall amounts through Saturday are forecast to range from 1 to 4 inches at lower elevations, and from 4 to 10 inches at the higher elevations of western Washington and northwestern Oregon. Moisture will also spread into the northern Intermountain West with a combination of mountain snow and valley rain possible Friday and Saturday. A series of cold fronts moving through the eastern U.S. today will move off the East Coast by Friday, with cooler and drier conditions setting up for much of the eastern U.S. Temperatures will be 3 to 8 degrees below average on Friday from the Ohio Valley to the Mid-Atlantic and Northeast. A few scattered rain showers, and possibly snow showers at the higher elevations, will be possible across the Northeast Friday morning. Conditions will generally dry out by Friday afternoon, however. Moisture and cloudiness should begin to gradually increase once again across the Northeast during the day on Saturday, with a few showers possible by late in the day. Ryan Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php