It’s been a warm September to date, punctuated by Thursday record-breaking 93-degree high, but cooler weather is arriving just in time for the start of astronomical fall which begins 8:54 pm Saturday evening. Saturday’s highs should peak only in the middle and upper 60s and Sunday morning’s lows should drop into the chilly 40s in inland locations. Warmer days will return, however, with the mercury once again pushing 80 degrees on Monday afternoon aided by increasing southwest winds. Another batch of cooler air is expected to arrive Tuesday night as a second cold front traverses the area, dropping Wednesday’s highs back into the 60s. A sure sign of the changing seasons, the week’s third cold front is expected to pass through the Chicago area Thursday night bringing more cool weather on Friday, though warmer weather is slated to return next weekend.