After a bitter freeze (like the one experienced during the first week of 2017), it may seem weird to then experience balmy conditions in mid-to-late January.
But this pattern does happen quite frequently, and it has a name -- the "January Thaw."
Most notably, the South and Northeast experience a period of well-above average temperatures while the Great Plains, Midwest, and Great Lakes regions become entrenched in bitterly cold, wintry weather.
This is due to a high pressure system that sets up near Bermuda -- known as the "Bermuda High" -- that drives warm, humid air into the eastern third of the country. The Bermuda High blocks the polar jet stream from diving south, effectively diverting it towards northeastern Canada. As a result, the South and East Coast enjoy temperatures that can climb 15 to 20 degrees above average.
In meteorology, the "January Thaw" is considered a statistical singularity, which the American Meteorological Society defines as "a meteorological condition that tends to occur on or near a specific date more frequently than chance would indicate."
For example, WGN chief meteorologist Tom Skilling says that Chicago experiences its thaw around January 20-22, "when the long-term average temperature breaks the freezing mark."
Closer to home, analysis of the top 10 warmest Januaries on record corroborate the theory of the "January Thaw":
1.) 1950: Max temperature of 77 degrees on Jan. 25.
2.) 1937: Max temperature of 77 degrees on Jan. 22.
3.) 1933: Max temperature of 78 degrees on Jan. 22.
4.) 1952: Max temperature of 79 degrees on Jan. 1; it should be noted that this particular year, temperatures ranged from the mid-40s to upper 60s during the days spanning from Jan. 20 - Jan. 28.
5.) 1974: Max temperature of 70 degrees on Jan. 22.
6.) 1949: Max temperature of 77 degrees on Jan. 10.
7.) 1916: Max temperature of 75 degrees on Jan. 11.
8.) 1923: Max temperature of 69 degrees on Jan. 31.
9.) 2006: Max temperature of 74 degrees on Jan. 2; it should be noted that for this particular year, temperatures spanned from the 50s to 60s during the days spanning from Jan. 20 - Jan. 28.
10.) 1953: Max temperature of 69 degrees on Jan. 15.