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The 2014 Farmers Almanac
Farmers' Almanac

What is a January Thaw?

What is a January Thaw?

Don’t be surprised if temperatures rise somewhat this week. The days surrounding January 25 have long been associated with the proverbial “January Thaw” when winter briefly loosens its icy grip.

But, exactly is a January Thaw? Is it real, or just another weather myth?

The January Thaw, like Indian Summer, is more than just another piece of fanciful weather lore. Annual averages really do show a slight temperature increase, and subsequent dip, during the final week of January. On average, January 23 is the coldest day of the year in much of the Northern Hemisphere. Almost exactly six months later sits July 24, the warmest day of the year, on average. Between those two dates, average daily temperatures show a fairly predictable rate of increase. While there may be deviations from that pattern during any given year, the model holds true when looked at over a period of several years.

Though predictable, the climb from cold weather to warm and back again, is not completely smooth. Small “blips” in the overall pattern reveal noticeable fluctuations that can be observed from year to year. These blips are called singularities in weather lingo. Indian Summer, a period of unseasonably warm weather that usually appears in mid-October, is one such blip. The January Thaw is another.

During the January Thaw, which usually lasts for about a week, temperatures rise an average of 10° F higher than the previous week, then drop back down in time for February’s arrival. Though it’s called a “thaw,” the January Thaw doesn’t necessarily melt away snow and ice during its stay. In areas where winter weather is exceptionally cold, temperatures during the thaw may not even rise above freezing. More temperate regions, however, may even experience what could be described as a “false spring.”

Though they are a verified weather phenomenon, January Thaws don’t happen every year. In order for a singularity like the January Thaw to be recognized, it only has to appear slightly more than 50 percent of the time.

That’s the beauty of weather; though predictable to some degree, it always keeps us on our toes.

If you notice a hole in the upper left-hand corner of your Farmers' Almanac, don't return it to the store! That hole isn't a defect; it's a part of history. Starting with the first edition of the Farmers' Almanac in 1818, readers used to nail holes into the corners to hang it up in their homes, barns, and outhouses (to provide both reading material and toilet paper). In 1910, the Almanac's publishers began pre-drilling holes in the corners to make it even easier for readers to keep all of that invaluable information (and paper) handy.