Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 344 AM EDT Tue Aug 26 2014 Valid 12Z Tue Aug 26 2014 - 12Z Thu Aug 28 2014 ...A threat for flash flooding is expected through early Thursday across the Central Plains and into the Middle Mississippi Valley... ...Hot and humid conditions will be commonplace over the center of the country... A split flow regime will be featured this week as an upper trough cuts off over the Central Great Basin. This system should gradually slide eastward with its forward motion being sluggish at times given its position well south of the prevailing westerlies. Moisture lifting into the Four Corners will interact with the advancing trough spawning an expansive area of showers and thunderstorms. Much of the activity should focus across the terrain where localized upslope flow will enhance vertical motions. The activity emerging off the higher terrain of the Rockies should carry a fairly organized thunderstorm complex into the Central Plains. There will be additional lift in the atmosphere as a west to east frontal boundary will be nearly stalled across the region. Multiple rounds of convection are expected as a series of impulses migrate eastward ahead of the approaching upper trough. An area spanning northeastern Colorado eastward through Nebraska and into Western Iowa is being highlighted for a threat for flash flooding. The WPC precipitation desks indicate areal averages of 2 to 4 inches of rainfall are likely through early Thursday across central to eastern Nebraska. While precipitation is likely from the Upper Great Lakes eastward into the northeastern states, it will be much lighter in nature. There are no discernible features aloft that will provide much of a trigger to sustain active convection. Any activity that does develop will form from daytime heating and weak lift along the advancing cold front. However, this frontal passage will usher away from the humid air developing by mid-week and allow cooler and drier conditions to settle in from the northwest. A surface high building in over the Great Lakes will bring tranquil conditions to much of the northeastern U.S. by later in the work week. The east to west boundary stalling across the center of the nation will maintain a fairly extensive temperature contrast. While highs in the 70s should be commonplace in the cool sector, it will be quite the opposite south of the wavy front. Hot and humid conditions are forecast to prevail over the Southern/Central Plains eastward into the Mississippi River Valley where highs push well into the 90s. Adding the element of humidity will make temperatures feel closer to 105 degrees Fahrenheit. An area of disturbed weather sliding westward across the Gulf of Mexico will enhance the threat for showers and thunderstorms, particularly along the Western Gulf Coast. This is where the better moisture is expected to be directed. Additionally, strong low-level convergence along an inverted trough is forecast along the Texas coastline which will enhance lift in the atmosphere. Rubin-Oster Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php