Sunday afternoon inland temperatures across the metro area warmed into the 60s at every reporting location - topped by a 66-degree reading at Midway. Rockford tied their all-time record of 64 for December 2nd set back in 1982. The adjacent water temperatures over Lake Michigan were 20 degrees cooler. The warm rising air over the city and cool sinking air over the water set the stage for a very efficient easterly lake breeze that started mid-afternoon. Air riding over the cool waters was mild and moist and cooled to condensation forming a fog bank that flowed inland covering much of the area with thickening fog, areas of drizzle and temperatures falling into the middle 40s. A Dense Fog Advisory was in effect overnight until mid-morning Monday.
Big warm-up and showers
As a cold front approaches from the west Monday, strengthening southwest winds gusting to 30 miles per hour will boost temperatures and effectively erase most of the fog during the forenoon. At the same time clouds along and ahead of the cold front will be increasing from the west. As temperatures peak in the 60s, showers and possibly a few thunderstorms will blossom in the afternoon spreading east across the Chicago area by evening. Behind the front, showers should end as winds shift to the northwest and and colder air sweeps into the area.