An increase in moisture from the south will cause dew points to rise from their current readings Tuesday, in the middle and upper 60's, into the lower to middle 70's Wednesday and Thursday. While a prolonged period of high heat index readings is not expected, a couple days with the heat index in the middle to upper 90's won't feel the greatest.
The bump in temperatures and humidity won't last because an incoming cold front Friday will
bring a chance for thunderstorms as early as Thursday evening. Better chance for storms over southern Wisconsin and northern Illinois will come late Thursday, and most likely Friday. The severe threat isn't looking overly impressive at this moment for Friday - mainly due to mostly cloudy skies - but heavy rainfall will be possible with any storms that do develop Friday afternoon.
Temperatures will be more seasonable heading into the weekend with highs in the low to mid 80's.