Explainer, PAUL MERZLOCK

The first half of December 2012 has brought a continuation of dry, mild conditions to Chicago. The month is  averaging 11 degrees above normal and there has yet to be a day with a sub-freezing high temperature. Normally a dreary month, this December has also been unusually sunny. Much of northern Illinois remains in a state of moderate to severe drought, causing lake and river levels to continue to fall. To date, this month has only produced 43% of its normal precipitation. Low pressure over the Southwest is forecast to become better organized on Friday. This means strong south winds ahead of this storm will keep temps well above normal. Rain is expected across the area Saturday, but forecast amounts are generally under a half inch. Colder air will arrive as the weather system passes east of the area on Sunday, but daytime temps are still forecast to run better than 5 degrees above normal.