Making sense of the late-January thaw
After five weeks of colder than normal temperatures, we've flipped to a warm pattern over the past week. I've heard many refer to this warm-up as a "January thaw." And I think that's a fair enough description. After all, for a period of 11 days, the average daily high was in the mid-30s and now 4 of the last 5 days have reached 50 or higher.
It's not at all uncharacteristic for temperatures to swing like this in the month of January. In fact, the commonality of January temperature spikes during the second half of the month following cold waves has motivated researchers to investigate whether the January thaw can be seen in the data and whether it's a real phenomenon.
Steve Zubrick, the Science Operations Officer at the National Weather Service Office in Sterling, Va., plotted the long-term data for D.C. and Baltimore (spanning over 130 years -- as shown above), and found some limited evidence for "thaw" like increases in temperatures early and late (around right now) in the month. But do we have any legitimate scientific explanation for the fact the warm-up seems to show up (on average) around the same time each year, or has it simply been recurring around this time by chance?
Zubrick doesn't think the coincidental timing is indicative of any real scientific phenomenon: "It's in the data, but is has no significance related to some known weather driver."
Zubrick referred me to a scientific paper published in 2002 entitled "Is the January thaw a statistical phantom?" that concluded about the January thaw:
...the observed warm spells are well within the limits of what might be expected to occur by chance alone in a stationary climate during any random period...
"... no dynamical basis, or even a plausible physical mechanism, has been advanced in the literature to explain why a warming in northeast U.S. temperatures should occur during this particular narrow time window."
In other words, the repeated thaw occurrence around this time is probably a statistical phantom or as Zubrick put it "a human un-scientific perception rather than a scientific reality."
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