This month is currently ranked the 5th warmest December on record. Saturday marked the 19th consecutive day of above normal temperatures. Readings Saturday evening topped the 50-degree mark for the second consecutive day. Chillier air is due to arrive on Sunday, with high temps through midweek forecast to average only 5 to 8 degrees above normal. Latest computer forecasts show the Chicago area trending much colder about Thursday. The Winter solstice occurs Friday at 5:12 AM CST. In line with the calendar, Friday is also forecast to be the first day this season with a sub-freezing high temperature. The influx of polar air is to arrive in the wake of a deepening storm system. This system may produce the season's first measurable snowfall on Thursday. Blustery winds are forecast to accompany the late-week turn toward colder weather.