Near the town of Petaquillas, Mexico, a man held on to a line Wednesday as he crossed a stream swollen by rain dumped by the storm Manuel. Alejandrino Gonzalez/AP hide caption

itoggle caption Alejandrino Gonzalez/AP

A man walks across the washed-out Wagonwheel Gap Road in Boulder, Colo., on Monday. Mark Leffingwell /Reuters/Landov hide caption

itoggle caption Mark Leffingwell /Reuters/Landov

John Hoffenberg watches as floodwaters flow down a street in Boulder, Colo., on Sunday. Mark Leffingwell/Reuters/Landov hide caption

itoggle caption Mark Leffingwell/Reuters/Landov

A city worker talks on his phone while surveying high water levels on Boulder Creek following overnight flash flooding in downtown Boulder, Colo. today. Flash flooding in Colorado has left two people dead and the widespread high waters are keeping search and rescue teams from reaching stranded residents and motorists in Boulder and nearby mountain communities. Brennan Linsley/AP hide caption

itoggle caption Brennan Linsley/AP

Quite a show in Chicago: Lightning struck the Willis Tower (formerly the Sears Tower, at right) on Wednesday as the storm system moved through. Scott Olson/Getty Images hide caption

itoggle caption Scott Olson/Getty Images

Friday's storm, which produced a mile-wide tornado, as it neared El Reno, Okla. Richard Rowe /Reuters /Landov hide caption

itoggle caption Richard Rowe /Reuters /Landov

After the storm: Sheet metal that was torn off a building during Friday's tornado in El Reno, Okla., ended up caught in a tree. Bill Waugh /Reuters /Landov hide caption

itoggle caption Bill Waugh /Reuters /Landov

Tuesday's weather is expected to be bad from Texas up into the nation's midsection and across to the Great Lakes. National Weather Service hide caption

itoggle caption National Weather Service