MILWAUKEE (WTAQ) - The heat wave of 2012 will last a little longer than what forecasters originally thought.

An excessive heat warning was supposed to end at 10 p.m. Friday in western, central, and southern Wisconsin.

But the National Weather Service says the effects of a cold front won’t get to southern Wisconsin until Saturday. So the warning has been extended until 7 p.m. Saturday for Madison and five surrounding counties – until 2 p.m. Saturday for five southeast counties outside of Milwaukee – and until 7 a.m. Saturday for Milwaukee and a pair of counties to the north.

Forecasters say the mercury will get above 100 again Friday afternoon in most inland locations in southern Wisconsin – and in the 90’s along Lake Michigan.

Middleton was already at 100 degrees at noon, while Kenosha was at 98. Places along Lake Superior were only in the low 70’s at mid-day.

The heat index is supposed to stay above 75 Friday night in the south – while in northern Wisconsin, Friday night’s lows will get down to the upper 50’s.

Southwest Wisconsin is supposed to return to the mid-90’s Saturday, while other parts of the Badger State will cool down to the 70’s and 80’s.

Thunderstorms are likely Friday night in the north before the cool down begins. There’s a chance of rain in all of Wisconsin Saturday except the far northwest.