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Weather Almanac for January 2002JANUARY THAW: WINTER COLD RELIEF  January Thaw: snow melts, ice thins, a hint of coming Spring fills the air. I feel a bit odd writing this article on the January Thaw in a region of Canada that often has little to thaw in mid-January, particularly this January. We have just finished three days (January 6-8) when over 50 British Columbia sites broke daily maximum temperature records, Victoria chipping in on all three of them. But as my regular readers well know, although my body resides in "tropical" Victoria, my mind and spirit still wander across the Great Lakes region. This year, a rare head cold over the holidays gave me much time for mental playback of my first four decades of cold winter memories. Prominent was the January Thaw. And given the recent weather headlines, this mild winter will likely not see a thaw being anticipated by residents back east, excluding perhaps the folks around Buffalo, NY.
Before I get into the debate over whether this weather spell is as real as we imagine, I need to define the term. The January Thaw, according to the 1954 Glossary of Meteorology published by the American Meteorological Society, is: "A period of mild weather, popularly supposed to recur each year in late January in New England and other parts of the northeastern United States....Statistical tests show a high probability that it is a real singularity." Further, a singularity is a characteristic meteorological condition that tends to occur on or near a specific calendar date more frequently than chance would indicate. Although there are no generally accepted weather parameters that specifically define it, the January Thaw should last for several consecutive days and have maximum daily temperatures above freezing and mean daily temperatures around 10Fo/5Co above the expected mid-January normals. A January Thaw is expected to fall within the third week of January, usually following a strong cold snap, but need not occur every year. In fact, during the very cold winters of the late 1970s, there were no January Thaws in the New England region during 1978 and 1979. (And they could have used a thaw!) There have also been recent mild winters when the Thaw was absent or hardly noticeable, as will likely be the case in 2002.
Often during this time, the upper air wind patterns are in a period of readjustment, and thus surface weather systems stall or creep slowly across the eastern continent's mid-latitude belt. After several days of warmth, the regional weather again comes under the influence of a strengthened polar high (F,G), and cold weather returns. The period of thaw usually results in a significant reduction of snow cover and ice thickness that is welcomed by many as a release from winter's uncomfortable grip. Those enjoying winter weather recreations -- sports and festivals -- often curse the January Thaw, however, for ruining ice and snow conditions. For them, a respite from bitter cold without the thawing is favoured.
Analyses by climatologists David Phillips of Environment Canada and Art DeGaetano of the Northeast Regional Climate Center at Cornell University show definite warm spikes in the climate records for many sites across the prime region during this period. The other side of the debate is characterized by papers such as one to be published this month in the Bulletin of the American Meteorological Society. In it, authors Christopher M. Godfrey, Daniel S. Wilks and David M. Schultz find no unique January Thaw period that is statistically significant, seeing thaws during this month as purely random events. And while they readily admit their analysis is not conclusive proof that no January Thaw exists, they remind us that no dynamic or plausible physical mechanism has yet been advance to explain why a winter thaw should favour any specific narrow period year to year. Godfrey, et al. do suggest one probable explanation for folklore and popular perceptions of so-called weather singularities such as the January thaw. "It is a recognized characteristic of human psychology that people will find patterns in the world around them, whether or not those patterns result from coherent underlying causes." This characteristic to see patterns in the surrounding environment, whether they exist or not, has served our species and many individuals well in the past and will continue to do so. Better we see the face of a non-existent tiger in the bushes and be wary than not see the face of a real tiger and be killed. That we see a pattern in the winter cycling of weather across certain regions which gives rise to a welcomed respite from the cold is a given. If it were not there, scientists would not have spent over a century trying to prove or disprove its existence. (For a further example of pattern recognition, read my essay on Cloud Men, and see if you can look at a well-developed cumulus cloud again without seeing a face.) Is the January Thaw real? I have to say emphatically, Yes! Not as a meteorologist/climatologist with proof irrefutable, but as a human who has seen its pattern unfold over decades of my life until it became a solid part of my personal lore. At times, I have cursed its coming when it melted away a good snow base for cross-country skiing. But more often, I welcomed its touch, and I do miss looking forward to a January thaw, living in a land where snow cover is rare. I think Hal Borland expressed the mystique of the January Thaw best in his book Sundial of the Seasons. "The January thaw is special because it opens Winter's door a crack just when it seems that the ice has locked it tight. Through that crack one can see the certainty of March and April somewhere up ahead....The worst one can say about the January thaw is that it never lasts. It lifts the heart, then drops it with a cold thud when the warm spell passes and the chill congeals the earth again....But when January does relent, even for a day or two, we can celebrate, cautiously." Learn More From These Relevant Books
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The January Thaw, which usually occurs during the third week of January across the Great Lakes/St Lawrence Valley, New England and the Maritime Provinces, holds a place in North American weather lore nearly as prominent as Autumn's Indian Summer. And as far as I can determine, it is unique to this continent, particularly the aforementioned regions, approximately east of the Mississippi River and between 40 and 50 degrees North latitude. (There are also January thaw periods common earlier in the month in the Prairie/Plains region.)
In prime January Thaw country, the ideal weather pattern characteristic of the Thaw period unfolds in this manner. It begins after a cold air mass from northern or western regions has slid over the region (A), eventually moving out over the Atlantic Ocean. As that air mass leaves, the Bermuda High strengthens (B,C,D) and becomes positioned over the southern Atlantic Coast or southeastern US states while a broad low pressure trough moves slowly across northern Ontario and Quebec (B-E). The juxtaposition of the isobar patterns of these two map features (E) places the northeastern US and southeastern Canada border region into a south-southwesterly flow of warm air from the Gulf of Mexico. This air advects over the northern snow and ice fields and begins a thawing.
All meteorologists would agree that a period of thawing is a common winter weather event in the mid-latitudes of the continent. Why such a thaw should have a preference for the January 20-26 period rather than being a purely random event is still an unknown -- if there is in fact such a preference. Whether there is a preferential calendar slot remains the subject of debate among climatologists.