Defining the January thaw
The January thaw -- or “Bonspiel” as we often call it in the Prairies -- is a period of relative warmth in mid-to-late January. The thaw usually occurs after a bout of unusually cold weather, so it would seem we are all due.
Tradition defines the thaw as a climactic phenomenon that takes place gradually over a period of two days to as long as week. During this period the temperature should rise to at least 2°C. For those who cherish or dislike winter, know that the thaw is also temporary and doesn't happen every year.
In meteorology and climatology, the January thaw is also known as a singularity. That is a weather event that is an anomalous departure from the average in a majority of years (but not all years), at about the same time on a calendar.
So, science can’t fully recognize it as real because it doesn't occur in the vast majority of years.
The Farmers Almanac offers that January 23 is generally the coldest day of the year, or the apex of cold weather in winter. From that date the trend is for our temperatures, on average, to begin rising.
You might have also noted that the days are getting longer again. On January 15, Toronto gets nearly 25 more minutes of daylight than it had on the first day of winter just over three weeks ago!
The suns energy is again re-warming our northern hemisphere. That renewed heating is also beginning to alter our winter weather pattern, allowing for a more zonal, or west to east flow in the atmosphere. That change, combined with the extra daylight, creates an opportunity for the January thaw.
Obviously the next verification of our transition from winter to spring will come on February 2, Groundhog Day.
Thumbnail image: Flickr- Meinvb