Thaw (weather)

January thaw is a term applied to a thaw or rise in temperature in mid-winter found in mid-latitude North America.

Sinusoidal estimates of expected temperatures, for northern locales, usually place the lowest temperatures around January 23 and the highest around July 24, and provide fairly accurate estimates of temperature expectations. Actual average temperatures in North America usually significantly differ twice over the course of the year:

During this "thaw" period, usually lasting for about a week, temperatures are generally about 6 °C (10 °F) above normal. This varies from year to year, and temperatures fluctuate enough that such a rise in late-January temperature would be unremarkable; what is remarkable (and unexplained) is the tendency for such rises to occur more commonly in late January than in mid-January or early February, which sinusoidal estimates have to be slightly warmer.