Why is it that the coldest part of winter is about a month after the winter solstice, and the hottest part of summer is about a month after summer solstice?

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Dear Tom,

Why is it that the coldest part of winter is about a month after the winter solstice, and the hottest part of summer is about a month after summer solstice? You would think it would coincide with the shortest and longest days? Thanks!

Doug Neufeldt,  Roselle

Dear Doug,

Your observations are right on. Chicago’s normal daily temperatures have been on a slow but steady decline since they peaked with a high of 85 and low of 67 during the period of July 11-24. That decline will end after the annual temperature cycle bottoms out with a normal high of 31 and a low of 18 during January 16-28, 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.”