Q: Why are cold snaps in autumn so short-lived?
A: Over the past weekend southern Wisconsin experienced its first cold snap of the season with widespread morning lows in the lower 30s on Friday and Sunday mornings.
Very often cold snaps in the autumn are very short-lived as this recent example was, affecting usually one or two nights at most.
There are a variety of reasons for this brevity.
First, cold snaps at this time of year require a substantial southerly excursion of cold air from high-latitude Canada to get us cold.
Though the Arctic night creeps ever farther south each day after the autumnal equinox, its southerly progress is slow.
Consequently, cold air production is limited to the very highest latitudes well into November, which means that any cold air that makes it as far south as Madison is not well-connected to a broader reservoir of cold air that would allow the cold to remain.
Second, there is little snow on the ground even in central Canada at this time of year and so the cold air that does migrate southward is modified (warmed) to a greater degree on that migration at this time of year than in the late fall and winter, when snow cover is widespread.
Third, the lack of snow on the ground in Madison itself limits the longevity of cold snaps. That’s even true in the wintertime.
Overnight cooling over a snowfield can reinvigorate the chill of a cold snap and render it longer-lasting as a result.
So, if you were complaining about the cold this weekend, be glad we are still in October and much more likely to experience a quick rebound.
Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at firstname.lastname@example.org or email@example.com.
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