From folklore to science: The 'January Thaw' is real, as the Northeast and Middle Atlantic states are about to find out

After 10 days of digging out from the Blizzard of '96, temperatures across the northeastern and middle Atlantic regions of the United States have begun to rise in what folklore calls the "January Thaw," according to a climatologist at the Northeast Regional Climate Center at Cornell University.

"The January Thaw has origins rooted in New England folklore and describes a period of a few days in mid- to late-January in which unseasonably warm temperatures have a tendency to occur," said Art DeGaetano, climatologist at the center.

Although the thaw does not have a fixed time of occurrence, climatologists note the most frequent thaws occur between Jan. 19 and Jan. 28. DeGaetano said the so-called thaw is most noticeable in the eastern United States, but can be traced as far west as Missouri.

Scientifically, the thaw is classified as a phenomenon known as a singularity, which refers to a reoccurring anomalous departure of temperature from its normal seasonal value, on or near a particular date.

In other words, the weather has become unseasonable at a specific time.

"Such phenomena are not a sure thing, as even the most pronounced singularities only occur in slightly more than 50 percent of the years," said DeGaetano. "During the remaining years, conditions, in the case of the January Thaw, may be colder than normal."

DeGaetano notes that although this lack of consistency makes it hard to statistically conclude that the thaw is something other than a random occurrence, there is a distinct tendency for this phenomenon to manifest itself in the northeastern part of the country.

Further, he notes that it is equally difficult to pinpoint a physical reason for the January Thaw to occur. The most widely accepted view is that during late January, upper level wind patterns undergo an adjustment.

During this adjustment, temperatures over the eastern United States are initially affected by a strengthening of the high pressure system over Bermuda, which initiates the thaw. Then, the weather become influenced once again by a strengthening polar high, returning the Northeast to colder temperatures.

"The observation that surf conditions or ocean currents change directions -- to those more typical of summertime -- during the January Thaw further support this theory," DeGaetano said.

The table below demonstrates the magnitude of the thaw by comparing average high temperatures on Jan. 20, 25, and 30 at several Northeast locations.

Average High Temperatures

Station Jan. 20 Jan. 2 Jan. 30
Baltimore 41 45 41
Boston 36 39 36
Central Park, N.Y. 37 42 38
Charleston, W.Va. 39 46 41
Hartford, Conn. 32 37 34
Newark, N.J. 37 41 38
Philadelphia 37 41 38
Pittsburgh 33 38 33
Syracuse, N.Y. 30 35 30
Washington, D.C. 42 45 43
Source: Northeast Regional Climate Center at Cornell University

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