Severe storms threaten area late in the day

A warm frontal passage and powerful humid winds that take hold Wednesday set the stage
for what could be a significant severe weather outbreak late in the day into Wednesday
night. Clusters of thunderstorms have flared overnight with the northbound front. An ensuing
flood of Gulf air into the area is to produce the most humid daytime humidities since
September. This will provide fuel for a new wave of thunderstorms expected to assemble into
a squall line in eastern Iowa on Wednesday afternoon then surge eastward, most likely
reaching the Chicago area between 7 and 11 p.m. Computer model energy calculations indicate
an atmosphere capable of fostering supercell thunderstorms, which all too often spawn
dangerous wind gusts and tornadoes.
The National Oceanic and Atmospheric Administration's Storm Prediction Center,
responsible for all of the country's tornado and severe thunderstorm watches, placed sections of
Illinois in a moderate risk three days ago. Issuing such a warning three days in advance
is something the agency has done only seven times in the country since 2001.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune