After the recent abnormally cold period, which has left us 3.2 degrees colder than normal thus far in September, a lot of people have been wondering if September temperatures can be a harbinger of what is to come in the winter.
Everyone recalls last winter as a persistently cold season during which we experienced a four-month period (December 1 – March 31) with an average temperature that was 7.44 degrees below normal. Interestingly, last September was 2.7 degrees above normal and last October was 1.0 degrees above normal.
Records from the preceding four winters (2009-10 through 2012-13) provide an interesting, though inconclusive, answer to this question. Of those four prior winters (December through February only), two were colder than normal — 2009-10 by 0.26 degrees and 2010-11 by 1.50 degrees. In 2010-11, September and October averaged 1.67 degrees warmer than normal, while in 2009-10 those same months were 1.14 degrees colder than normal.
The winters of 2011-12 and 2012-13 were 7.01 and 1.32 degrees warmer than normal. Their corresponding Septembers/Octobers were 0.74 degrees warmer and 0.35 degrees colder than normal.
Thus, based upon a very small but recent sample, one might tentatively conclude that abnormal cold or warmth in September and October has little to do with the nature of the coming winter. The most recent three-month outlook issued by the Climate Prediction Center is equally inconclusive for the Midwest, suggesting equal chances for colder- or warmer-than-normal conditions for our months of September, October and November.