Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 356 AM EDT Sun Oct 18 2015 Valid 12Z Sun Oct 18 2015 - 12Z Tue Oct 20 2015 ...Flash flooding possible for portions of the western U.S... ...Temperatures will be well below average today across the eastern U.S... An upper-level trough will move into the western U.S. today along with the associated surface frontal system. The front will move slowly across the Intermountain West through Monday -- this along with a continued moist and unstable air mass in place will promote scattered to numerous showers and thunderstorms across much of the interior western states. Showers and thunderstorms will be the most numerous today from portions of the Great Basin region into portions of the Southwest, where heavy rain and flash flooding are possible. An area of Canadian surface high pressure will remain in place across the eastern U.S. today. This surface high is associated with a cool and generally dry air mass. As a result, high temperatures today across the eastern U.S. will once again be 10 to 20 degrees below average for many areas. A few scattered rain and snow showers will be possible for portions of the Great Lakes and Northeast. The surface high will slide offshore by Monday and temperatures will begin to moderate in earnest. A fast-moving cold front will move from Canada into the Midwest/Upper Great Lakes Monday night, bringing scattered areas of showers from the northern plains to the Northeast. Snow may once again mix with rain showers across portions of northern New England, generally at higher elevations. Ryan Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php