ASK TOM: When do winter temperatures bottom out?

Dear Tom,
Is there an accepted period when the descending temperatures of winter bottom out?
— Mel Dormer,  Aurora

Dear Mel,
Chicago’s normal daily temperatures have been on a slow but steady decline since they peaked with a high of 85 and low of 64 during the period of July 9-15.

That decline will end after the annual temperature cycle bottoms out with a normal  high of 31 and a low of 16 during January 11-27, after which readings will once again begin to rise.

It is interesting to note that both the city’s warmest and coldest times of the year come three to four weeks after the solstices as the Earth continues to gain heat in summer and lose heat in winter following the longest and shortest days, in what is known as the “lag of the seasons.”