Thaw is the period when the

snow Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout ...

and

ice Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...

melt, at the end of the winter, in cold climates.

January thaw

January thaw is a term applied to a thaw or rise in temperature in mid-winter found in mid-

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

Sinusoid A sine wave, sinusoidal wave, or just sinusoid is a mathematical curve defined in terms of the ''sine'' trigonometric function, of which it is the graph. It is a type of continuous wave and also a smooth periodic function. It occurs often in ma ...

al 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 * Mid-autumn temperatures tend to be warmer than predicted by the

sinusoidal model In statistics, signal processing, and time series analysis, a sinusoidal model is used to approximate a sequence ''Yi'' to a sine function: :Y_i = C + \alpha\sin(\omega T_i + \phi) + E_i where ''C'' is constant defining a mean level, α is an ...

, creating the impression of extended summer warmth known as

Indian summer An Indian summer is a period of unseasonably warm, dry weather that sometimes occurs in autumn in temperate regions of the northern hemisphere. Several sources describe a true Indian summer as not occurring until after the first frost, or more s ...

. * For five days around January 25, temperatures are usually significantly warmer than predicted by the sinusoidal estimate, and also warmer than neighboring temperatures on both sides. 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. In some regions (such as northern

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

) this phenomenon will not be manifest as a "thaw" in the technical sense, since temperatures will remain below freezing. The January thaw is believed to be a weather singularity. A possible physical mechanism for such phenomena was offered in the 1950s by E.G. Bowen: he suggested that some "calendaricities" (as he called them) might be explicable in terms of meteoric particles from cometary orbits acting as ice nuclei in terrestrial clouds; his theory then received some support from several sources. However, Bowen's ideas later fell out of favour with the development of atmospheric dynamic modelling techniques, although one of his rainfall peaks does seem to correspond with the date of the January thaw. Data analysis has not found statistically significant support for the supposed January thaw. The authors of this study state that "the effects of sampling in finite climate records are wholly adequate to account for the existence of January thaw 'features' in northeastern U.S. temperature data."

References

External links

"January Thaw: Winter Cold Relief""January Thaw"
''The Canadian Encyclopedia'' Weather lore Winter phenomena Snow {{climate-stub

January thaw

See also

References

External links