Is the Winter Solstice the Source of the January Thaw?

Factual Questions
1

Every year, in January, after the Winter Solstice (December 21-22), there is often a period of calm, warm weather that mimics the “Indian Summer” of Fall.

This year, where I live, it ran for a total of about 10 days. Maximum daytime temperature rose from roughly +40F to a high of +59F. Nighttime lows showed lesser change. Snow and ice disappeared, melt-water ran in gutters everywhere. A few sluggish flies came out to circle in the sunlight at the height of the day’s warmth.

The Internet tells me this unseasonably mild weather is called the “January Thaw” or the “Winter Thaw,” and that it’s a common meteorological phenomenon akin to “Indian Summer.”

Various online sites describe it in meteorological jargon, but claim that among scientists it is unclear whether this is related to the Winter Solstice. The Winter Solstice is the moment when the Earth reaches the farthest point of the South Pole’s tilt towards the sun, marking Summer in the Southern Hemisphere, and (conversely) the first day of Winter in the Northern Hemisphere.

I assume that the Earth reaches a point of perfect stasis in this tilt, then recovers to begin a slow acceleration towards the perfect middling of the next Equinox, with the Sun directly overhead at the Equator (marking the first day of Spring in the Northern Hemisphere).

–My question is whether this December 21-22 stasis in the Earth’s tilt is the originating cause of the brief but dramatic change sometimes seen in January weather? Why would a weather window like that occur at all, why the delay, and why does ordinary winter weather soon return with a vengeance?

When scientists say they don’t know, sometimes they mean, “We don’t know, really,” and sometimes they mean, “We think we know by theory, but won’t say so because we don’t have data to prove it.”

Anyone in the weather or science business want to clarify which it is here?

2

Where do you live? Do you have meteorological data which shows that this phenomenon actually exists?

3

No, it’s not like the earth is rocking back and forth. The axis always points in the same direction (to a first approximation, and ignoring the 26000 year precession). The solstice is just that point in its orbit where that direction is directly toward or away from the sun, and there’s no reason why the temperature should dramatically increase at that point. I suspect that if you go back far enough, the number of cold snaps will equal the number of thaws.

4

Just as “Indian Summer” doesn’t always occur (there’s no clear-cut definition of it, but the term is typically used to refer to a warm spell occurring in the fall, after a “killing frost” has occurred), the “January thaw” doesn’t always occur, either. It does, in many areas, happen often enough that the concept of “January thaw” endures in people’s minds, but it’s by no means a guarantee.

January is typically the coldest period of winter in the Northern Hemisphere, and so, a warm spell is noteworthy (which is why the idea of a "January thaw"sticks in people’s minds), but there’s no particular magic to it being “caused” by the Winter Solstice, any more than it is caused by the disposal of Christmas trees or the coming of the Magi.

5

Indian Summer is generally described as an unseasonal warm period occurring (1) after the Autumnal Equinox after a full moon, and (2) after the first hard freeze of the season. Wikipedia offers something similar. Mine came from a NOAA meteorologist. NOAA currently has (PDF warning) …

NOAA isn’t so detailed with a January Thaw …

6

A few milder days after the first cold snap in January feels like a “thaw.” Nothing more significant than that. (New Englander here.)

7

I imagine this is mostly the OP’s imagination. The perihelion does occur around January 3-5 (so that the earth would be further away from the sun in both late December and mid January than it is at the beginning of January), but this has a negligible impact on temperatures. The eccentricity of Earth’s orbit is only 0.017, which means it is very close to circular. And after all, nobody thinks it gets especially cool around the Fourth of July, which is the time of the aphelion.

8

I remember reading something about this in Glenn Trewartha’s The Earth’s Problem Climates. I don’t have a copy handy. The book is about 50 years old, so it probably has been superseded by more recent research. From what I remember, a brief mid-winter thaw recurs with reasonable regularity at about the same time of year (mid-to-late January) in some limited parts of the world, and so is considered to be a climatic “singularity” in those areas. It is not, however, anywhere near universal around the globe, nor even the northern hemisphere. I forget if he had an explanation for what causes it.

9

I doubt that is has anything to do with the Winter Solstice. People just happen to remember the first nice stretch after a long cold period. Confirmation bias.

Here on the Oregon Coast it is usually a nice week in February. I have been walking on the beach in 70 degree (F) weather in February when it won’t get that warm again until May. And it isn’t just me, here is an unscientific support article on the Mini Spring of February from 2009. I can hardly wait. If it comes. If it doesn’t I’ll forget this year and hope for next year to confirm.

10

Interesting answers.

I hope “DJ” on the Oregon coast isn’t walking the beach at Waldport, where all my old college friends lived (either there or in Otis Junction, near Lincoln City).

In researching this a bit more in response to the answers here, I found these opinions on it…

http://www.islandnet.com/~see/weather/almanac/arc2002/alm02jan2.htm

…the first being the more complete discussion. Both say the phenomenon is “real,” if controversial. My local Utah observation is anecdotal.

If we can not be certain the phenomenon even exists, clearly it can’t be connected to the Solstice in any theoretical manner. That’s an answer: thanks.

I’m still working on visualizing how the solstice works. So, the earth doesn’t tilt back and forth, but it’s permanent tilt is presented to the sun at changing angles? Makes sense. Guess I’ll go look for a good diagram on the Net.

11

A side note: In Alaska, this phenomenon is called a “chinook” and is characterized by warmer temps and winds that remove all the snow. Sometimes it even rains in the dead of winter. This typically happens several times during winter, but I don’t recall it being associated with solstice. In fact, this winter is breaking records for sub-zero temps in January in Anchorage.

12

Here’s a good picture of what’s happening:
http://www.astro.cornell.edu/academics/courses/astro201/seasons.htm

13

Not only in Alaska.

14

Thanks, Brocks.

Yes, that’s what I was seeing, on reboot. Interesting that I got through high school and college without understanding this clearly. Nobody quite burned through the haze on it or I forgot it after many years.

Chef Guy:

There is a story on Drudge today that a new low temp for the U.S. of -85 was being set in Alaska when the thermometer broke. It’s in a place called “Jim River,” of which I’ve never heard.

15

Don’t feel too badly. I took a survey-level Geography class when I was in college (it was, for me, an easy and fun way to fill up some elective credits with an easy “A”). When the professor explained that we have seasons because the Earth’s axis is tilted, it was clear that this was real news to an awful lot of my fellow students.