Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 337 AM EDT Sat May 18 2019 Valid 12Z Sat May 18 2019 - 12Z Mon May 20 2019 ...Severe thunderstorms and some flash flooding can be expected across portions of the Plains, Mississippi Valley and Ohio Valley this weekend... ...Much cooler than normal temperatures will continue for much of the western U.S. and the northern Plains... A series of cold and energetic upper-level troughs will continue to bring active weather across the western U.S. through the weekend. This will allow unsettled weather and very chilly temperatures to continue for much of the West and out across the northern Plains. In fact, the higher elevations of the Intermountain West and the northern Rockies will be cold enough to see accumulating snow, some of it locally heavy, while valley locations will see a chilly rain. Even some areas of the northern High Plains will see some rain mixing with or changing over to wet snow before tapering off Saturday night. High temperatures in some locations will again be as much as 20 to 30 degrees below normal through the weekend, and this very cool and unsettled pattern should last into early next week. Meanwhile, energy ejecting from the lead upper-level trough continues to edge east out across the Great Plains, and this will result in multiple waves of low pressure moving across the central Plains along a strong front. This will drive multiple rounds of widespread heavy showers and thunderstorms with a focus on the central and southern Plains and also adjacent areas of the lower to middle Mississippi Valley Saturday through Saturday night. Some of the thunderstorms will be severe, and the Storm Prediction Center has highlighted much of this region in a Slight Risk of severe weather, including an Enhanced Risk area for the ArkLaTex region. Large hail, damaging wind gusts, and a few tornadoes will be the concern with the stronger thunderstorms. In addition, heavy rainfall will likely result in some areas of flash flooding across these same areas, and the Weather Prediction Center has highlighted a Slight Risk of excessive rainfall as a result and including areas a bit farther north over the upper Midwest where a Moderate Risk has been highlighted. On Sunday, with a cold front advancing off to the east, the focus of showers and thunderstorms will shift off to the east as well and include much of the Great Lakes region, the Ohio Valley and areas to the south including portions of the western and central Gulf Coast. The main threat for severe weather should be over the Ohio Valley where the Storm Prediction Center currently has highlighted a Slight Risk area. The main threat for flash flooding on Sunday will likely be farther north over portions of the upper Midwest and upper Great Lakes where heavy rainfall falling over very wet and sensitive soil conditions will enhance runoff concerns. By later Sunday, the next storm system system upstream over the Pacific Ocean will begin to move onshore across the West Coast, bringing another round of widespread precipitation across the western U.S. including locally heavy rain and yet again some high elevation snow for California and portions of the Intermountain region going into early next week. The remainder of the country including the southeastern third of the country should be very warm and humid as a weak area of high pressure continues to nose in from the southwest Atlantic and helps to facilitate generally dry weather outside of a few showers. Orrison Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php