Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 338 PM EDT Fri Sep 04 2015 Valid 00Z Sat Sep 05 2015 - 00Z Mon Sep 07 2015 ...Heavy rainfall possible for portions of the northern Intermountain West, northern plains, and Upper Midwest... A nearly stationary frontal boundary is draped this afternoon from the northern Intermountain West eastward across the northern plains. Due to upper-level flow that is parallel to the surface boundary, the front will remain largely in place through Saturday. A relatively strong upper-level trough currently moving into the Pacific Northwest will move east by Saturday night into Sunday, causing a low-pressure system to deepen over the northern plains, and moving the entire frontal system eastward. Several weak waves of low pressure will migrate along the stationary frontal boundary through Saturday, bringing rather widespread rain and thunderstorms from the northern Intermountain West to the northern plains and Upper Midwest. The upper-level trough will bring sufficient cold air at the mid-levels for rain to mix with snow at the higher elevations of Montana, Idaho, and Wyoming. Due to the duration of rain and thunderstorms, heavy rainfall is possible from portions of the northern Intermountain West eastward across the northern plains to portions of the Upper Midwest. Some areas may receive 1-3 inches of rain through Sunday. A weakening cold front is moving southward across the Mid-Atlantic states this afternoon. The front will usher a drier and somewhat cooler air mass into the Mid-Atlantic states for the weekend, with afternoon high temperatures Saturday and Sunday expected to be slightly below average. Scattered showers and thunderstorms will be possible in the moist and unstable air mass ahead of the front, from portions of the Ohio valley into the southeastern states. Monsoonal moisture will remain in place across the southwestern U.S., with scattered showers and thunderstorms expected during the afternoon and evening through the weekend across the Four Corners region. Ryan Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php