A cold front will extend across the northern Plains, the upper Midwest, the Great Lakes and the Northeast on Wednesday. As warm, muggy air interacts with this frontal boundary, widespread rain and thunderstorms will develop across the Mississippi Valley, the Ohio Valley, the Mid-Atlantic and the Northeast. Heavy rain associated with these thunderstorms will bring a chance of flash flooding to a handful of states, including West Virginia, Pennsylvania, New York, Connecticut, Massachusettes, Vermont, New Hampshire and Maine. Heavy rain and thunderstorms will also develop along the western Gulf Coast, while scattered showers and thunderstorms will be possible over the eastern Gulf Coast and the Southeast.
Meanwhile, a separate cold front will stretch across the Great Basin and the Intermountain West on Wednesday. As this frontal boundary collides with humid air over the Plains, strong to severe thunderstorms will develop over eastern Colorado, western Kansas, western Nebraska, eastern Wyoming, western South Dakota, southeast Montana and southwest North Dakota. These thunderstorms will capable of producing large hail, dangerous straight line winds and isolated tornadoes. In addition, scattered showers will push across parts of the Pacific Northwest and the upper Intermountain West. High pressure will keep conditions clear across the Southwest on Wednesday.