September temps heading to subnormal finish
September’s projected average temperature, 63.2º, comes in at 0.6º below the month’s climatological normal of 63.8º, noteworthy in that it ends a string of eight consecutive months during which Chicago’s (monthly) temperatures ran above normal. In addition, based upon preliminary temperature reports for the first 27 days of the month, September temperatures will average below normal across all of Illinois.
But don’t give up on summer just yet. In a weather pattern reversal characteristic of this time of the year, persistent northwesterly upper-level winds that have delivered several cool outbreaks in recent weeks are about to give way to southwesterlies. In response, Chicago’s temperatures will surge 45° from the middle 40s Saturday morning into the middle 80s Monday afternoon. A few showers and thunderstorms will accompany the warm-up, though they will be sporadic.
-Richard Koeneman -WGN-TV Meteorologist