Chilly October likely to end wet then warm

October often brings Chicago some of its nicest weather before the dark, dreary, chilly days of November and December set in. However, October this year has been November-like, with persistently cloudy,chilly, wet weather. Through Sunday the month has had just 39 percent of its possible sunshine, on par with November's typical 40 percent. The city has recorded nearly twice as many days with precipitation as usual and already ranks as one of the wettest Octobers, with a week remaining. It has been cool, as well, with temperatures well below normal. Bucking historic trends, October 2009 has yet to record one 70-degree day in a month that normally produces eight. The upcoming week promises a continuation of the cloudy, wet weather, but a break in the rain on Thursday coupled with strong southerly winds ahead of a Plains storm system has the potential to send the mercury surging to 70. The warm-up will be brief, with temperatures dropping into the upper 30s by Halloween morning. But afternoon sun should send the mercury back to about 50 for trick-or-treaters.