Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 331 PM EDT Sat Oct 20 2018 Valid 00Z Sun Oct 21 2018 - 00Z Tue Oct 23 2018 ...Heavy rainfall threat the lower Texas coast and Rio Grande Valley... ...Much colder air across the Midwest and eastern U.S.... A slow-moving frontal boundary extending from the southern Mid-Atlantic region to the Gulf coast region will continue to provide the focus for showers and thunderstorms as it pushes slowly southeast this evening. As the front begins to move onshore and high pressure settles in, most areas from the southern Plains to the Mid Atlantic region are expected to see drier conditions through the remainder of the weekend and into the early part of next week. However, as the front stalls over the northwestern Gulf of Mexico, the lower Texas coast and Rio Grande valley are expected to be a primary exception, with persistent moist onshore winds north of the boundary supporting periods of locally heavy rain beginning later today and continuing through Sunday. Given recent heavy rains and wet soil conditions, a flash-flood watch is effect for this area beginning this evening and continuing through early Monday. An organizing area of low pressure along the front may begin to track to the north, extending this heavy rainfall threat further north along the Texas coast on Monday. Further to the north, a vigorous reinforcing shot of colder air will push southeast from the upper Midwest and Great Lakes into the Ohio valley and central Appalachians this evening and overnight. In addition to ushering in some of the coldest air of the season so far, showers and thunderstorms and gusty winds can be expected as this system pushes through. Temperatures from the Great Lakes to the southern Plains and through much of the eastern U.S. are expected to be below-normal, with some areas well below-normal on Sunday. Freeze warnings and frost advisories for Sunday morning currently extend from portions of eastern Kansas and Oklahoma to the southern Appalachians. In the West, a broad upper level system is expected to move into the southwestern U.S., bringing temperatures down while supporting showers and thunderstorms across portions of the Southwest and Great Basin beginning later today and continuing into early next week. Meanwhile, dry conditions and above normal temperatures are forecast to continue from northern California and the Pacific Northwest into the northern and central High Plains. Pereira Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php