Gulf moisture brings widespread rain
The Gulf of Mexico is "open for business" as a strong low-level jet stream drags moisture from 80° waters quickly northward Monday. As a result, an expanding area of significant rainfall spreads northward from the Texas coast, reaching Chicago by noon. Rain will continue into the night, but the responsible upper-level jet will move eastward along with the rain on Tuesday. By then, the still-expanding rain shield will cross the Appalachians into the Atlantic seaboard for Election Day, including thunderstorms and heavy rain in the central Gulf states.
Thereafter, massive high pressure will take up lodging in the Great Basin, spawning occasional breakaway high pressure cells which will drift east across the Midwest and cause extended dry weather for the rest of the week, with a gradual cooling trend to follow.
--Dennis Haller, WGN-TV