* WHAT...Thunderstorm activity through late this afternoon will create varying currents, rapid water level fluctuations, and dangerous swimming conditions with waves 3 to 5 feet expected. Northerly winds will develop tonight and create high wave action and dangerous swimming conditions with waves 6 to 9 feet expected.
* WHERE...In Illinois, Lake, Northern Cook and Central Cook Counties. In Indiana, Lake and Porter Counties.
* WHEN...Through Wednesday morning.
* IMPACTS...Swimming conditions will be life threatening, especially for inexperienced swimmers. For information on swim advisories or bans at Chicago beaches: www. cpdbeaches. com.