Technically speaking, Indian Summer is simply referred to as warm and dry (typically sunny) conditions occurring in late autumn. Many times, it is used only after the first killing freeze of the fall. However, that is not a rule that is written in stone. The other aspect of the definition is that it cannot be one warm and sunny day. It has to be a period of days strung together in a row of warm and sunny conditions. That may occur late this week in the Rockford region. After seeing highs struggling to reach 50° Wednesday, upper 60's and lower 70's -- possibly warmer -- return by Friday and Saturday. The asterisk in the equation will be cloud cover. Skies could very well be partly to mostly cloudy on both afternoons, which technically is not "sunny" as the definition of Indian Summer suggests.
Nonetheless, warmer air is set to return for Friday and Saturday behind strong southerly winds. After a brief cool down on Sunday, temperatures are poised to ramp right back up into the upper 60's and lower 70's! That will provide excellent conditions for those heading out and Trick-or-Treating!
As it looks now, lower to upper 60's will be present under a mostly cloudy sky during the early evening hours on Monday. Winds will be breezy out of the south, which may cause some of your Halloween decorations to blow around a bit. Otherwise, it looks like a perfect day for Halloween festivities. Of course, last year Halloween featured rain and a high temperature of only 52° in Rockford.