About three weeks or so ago the temperatures rose to over freezing -- into the 40s, actually. It was in January. My fingers have stopped being numb from the cold snap that followed, so now I can write this knowledgeable piece about the January thaw.

"Well, January thaw has arrived," I said to a bus passenger as we waited for departure time.

"What's January thaw?" she asked.

She was younger, and I realized that probably many younger people didn't know what January thaw was. No one twittered it, I guessed, which was a fascinating guess because I have never seen a twitter.

I've heard some birds twitter, a few more during this recent January thaw than during the numbing cold before and after it.

I went to Google, where a whole bunch of sites appeared magically. Nobody twittered on any of those sites. But they did write...writing I understand. I don't understand how people twitter.

"January thaw seems to have set in," wrote someone on the first site.

The writer described the temperatures, adding, "...but it is still jacket weather."

The writer talked about the neighbors going snowshoeing, dealt again with the temperatures, and ended the discussion by saying how, unlike the neighbors, he -- named Charles from Grand Isle -- liked his electricity ready to plug into at a wall socket.

Hey, that was great. Now what's January thaw?

"As Maine experiences a January thaw, environmentalists are releasing a report that says the region faces more thin ice, shorter ski seasons and more winter flooding in the years ahead due to global warming," began an Associated Press article.

That's also interesting. What's a January thaw?

So I checked with the National Weather Service for information.

Joseph Hewitt, a senior forecaster with the National Weather Service in Caribou, wrote, "Generally speaking ...our January thaws take place in mid to late January. However, as we saw this past January, we can get them in the first or second week. They tend to last 2 to 3 days and then a replacement of much colder air follows(sometimes an Arctic Blast). We have seen in past years where a January thaw did not take place, as was the case in January 2008 with the record snowfall."

All right, we're gaining here. We now know when they take place and about for how long. And, at least this year, I certainly agree that it was ended with an "Arctic Blast."

But what's a January thaw?

"Hypothesis tests based on time-series models with smoothly varying climatologies (i.e., with no anomalous features such as the January thaw, by construction) are used to evaluate the statistical significance of the observed January thaws. The synthetic series produce many apparent events of similar character and magnitudes, although occurring randomly throughout the year and equally divided between warm and cool deviations. It is thus concluded that the effects of sampling in finite climate records are wholly adequate to account for the existence of January thaw "features" in northeastern U.S. temperature data," led off scientist David M Schultz of NOAA's National Severe Storms Laboratory in Norman Oklahoma in an article on an American Meteorological Society Website. The article was to have been published in the January 2002 issue of the Bureau of American Meteorological Society bulletin, but some things never change and I was impressed by what I learned from it...that is, from the parts I could understand.

I think this scientist verified that there is such a thing as a January thaw. But what is it? What causes it?

"Meteorological conditions that tend to occur on or near a specific calendar date more frequently than chance might suggest have been termed singularities (e.g. Huschke 1959) or calendaricities, a term introduced by Brier et al. (1963) to avoid confusion with the mathematical usage of 'singularities.' These features are commonly identified as consistently observed warm or cold departures from the annual march of temperature, or as wet or dry departures from some background annual precipitation trend," Schultz continued in his introduction.

I think that means something occurs on a fairly regular basis that is different than what is happening before and after it.

Now we're getting there. It's something that happens on a regular basis.

Hey, wait. I already knew that. The January thaw happens in January, and while it is happening, temperatures rise a bit.

They rose at our house so much that warmer night with all the rain that we lost all the snow on our roof. Most of the ice on our driveway melted, but no mud appeared. This was great. I could get ready to leave for work without tippy toeing so as not to slip and break my crown -- or whatever other part hit the ice first.

I remember one dark, bleak, January night when we lived over in western Maine, hearing the water drip off the roof. This was January thaw, all right, but it was still a dark and scary night.

"Greely (1888, 117-119), Nunn (1927), Wahl (1952), and Lanzante and Harnack(1982) found that the warmth of the January thaw in the northeast United States was associated with southerly flow from a midlatitude cyclone tracking over the northern states. The January thaw was terminated by a shift to colder, northwesterly flow over New England associated with a continental anticyclone and an offshore trough (Wahl 1952). Aloft, Dickson's (1959) composite 500-hPa maps and Lanzante's (1983) composite 700-hPa maps are consistent with the results for the surface. Dickson's (1959) 500-hPa maps showed southwesterly flow over the eastern United States during the January thaw becoming more zonal after the January thaw, associated with rising heights centered over Louisiana and falling heights centered over Maine," this NOAA scientist continued.

Now we're getting somewhere. It appears to be caused by a "...southerly flow from a midlatitude cycline tracking over the northern states," Schultz's paragraph above states.

Too bad that according to Schultz and Hewitt, January thaw appears to be followed by a cold spell. Be much nicer if it were followed by a warmer-yet spell.

That cold spell happened all right after this year's January thaw. Hasn't let up yet.

Okay, now we may know what the January thaw is, what causes it, what follows it.

Schultz's article on some Website goes on for about eight or ten more pages and includes stuff such as math. Hey, why read all that? I told my high-school geometry teacher I just couldn't understand that math topic. In sympathy or out of frustration, she gave me a D- for the course.

It's enough for me to know that it gets warmer for a few days during January thaw. I hope that younger bus passenger reads this, because it's too much for me to try to explain -- even if I understood it.

Next question: when's mud season start? That's when the cold generally does not return right afterward. Blackflies and mosquitoes do, after some April snowstorms that the well-known expression calls "April showers."

So, I'll add to the information a bit. January thaw is after and before really cold weather and before mud season.

Hey, bring it on. I can't wait for mud season. Our driveway only muddied up for a day or so last spring, and not very deep at that.

And our road is paved.

Milt Gross can be reached for corrections, harassment, or other purposes at lesstraveledway@midmaine.com

Milton M. Gross Copyright 2010