Winds produce seiche, later slam Chicago area

Wild weather hammered sections of the Chicago area in stages Friday. The day began
with a seiche along Lake Michigan. Seiches occur when lake levels gyrate rapidly in
short periods of time, and they are produced when fast-moving squall lines push
domes of water into the Michigan shoreline. The waves are reflected back to Chicago
and when this happens, produces the oscillating lake levels. Friday's seiche, which
occurred between 6 and 7 a.m., involved 26-inch variations in just minutes -- changes
amplified in spots by the shape of the shoreline.
Then, powerful winds gushed out of collapsing thunderstorms late morning and
midday. Hardest hit were sections of Lake and McHenry Counties where winds gusted
above 60 m.p.h., snapping trees and power lines and flipping a semi on Interstate
Highway 90 in McHenry County.
The day's third wave of storms bombarded the far southern suburbs near Kankakee with
huge hail the size of tennis balls. The hail fell so prolifically from 57,000-foot-tall
storms, it covered the ground. Torrential rainfall at Milford in Iroquois County -- 60
miles south of Chicago -- generated more than 6 inches in just two hours. A series of
tornado touchdowns Downstate on Friday included one in Springfield.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune