According to the heavenly bodies, it is winter now. The winter solstice occurred at 11:11 AM CST (or 1711 UTC), Saturday, December 21, 2013. This is the moment when the sun's most direct rays reach the southernmost latitude, 23.5 degrees South, the Tropic of Capricorn. From now on, the sun's rays will move further and further north as the Earth's tilt changes with its yearly rotation.
The transition to this point has been marked by quite a weather wallop over the past month or so. But it's all in keeping with the big picture of the weather story in a midcontinental, midlatitude location like Chicagoland. This part of the globe is transitioning from the warm summer season to the cold winter, and the transition can really send us for a thrill ride.
After a relatively benign start to November, a weather system moved in on November 11. It started out as rain, but as temperatures began to fall, it turned over to accumulating snow. It ended that same evening, but it was a different story over in northwest Indiana, as the lake-effect snow machine turned on, as cold northerly winds blew off still warm waters of Lake Michigan. As befits the incredible amount of variability spatially speaking, amounts throughout that area ranged from a light accumulation well under an inch in Valparaiso to nearly 4 inches just 4-5 miles away in Wanatah.
But all that snow was a memory by the following weekend when warmer air rode into the area on southwesterly surface winds. Well above the surface, a strong jet (concentrated area of fast winds) formed, blowing at 130-150 mph. This helped air to rise in earnest and combined with very moist air and some other factors, triggered powerful thunderstorms, which produced tornadoes throughout the Midwest.
It was so interesting when, while at my grandma's hosue, the NOAA weather radio sounded and the warning specifically alerted people at Soldier Field to seek safe shelter--while a game was in progress.
Once the stormy weather and its associated low pressure system passed, temperatures went down, all the way to the 20s for the high by Saturday, November 23. After it passed bringing a slight warm-up, temperatures went down again, though not as drastically. Then, temperatures began to go up again as we entered December. The pinnacle came on the night of Wednesday, December 4, when the temperature reached 56 degrees at O'Hare Airport at about 7:50 PM CST. I went to Advent Evening prayer in a lighter jacket and short-sleeved shirt. It kind of reminded me of the beginning of last December, when temperatures got near 70.
But that became a memory as temperatures plummeted overnight and became bitterly cold by Saturday. There was quite a stretch of cold weather for days as winter got kicking a lot sooner than last year. A slight warm-up came, followed by a big snowmaker on December 14, and then more cold. And then there was another warm up toward the end of this week, enough to melt much of the snow that had fallen a few days before.
So yeah, it's been a bit wild, but this is the time of year for these types of weather situations to occur, with constant fluctuations in temperatures, and lots of different kinds of precipitation. It all happens as one weather system comes after another, driven by a much stronger difference in temperature over the continent as cold air intrudes further south, with warm subtropical temperatures persisting near the southern US border. And Chicagoland certainly isn't the only spot in the United States to have had such weather, as many other locations in the South and East Coast have, too.
From what I know of the latest climate outlooks, Chicagoland is expected to have a winter with average temperatures and snowfall, though there's a possibility there could be above average snowfall. Ultimately, we'll find out what kind of winter we'll have as each day comes, so stay tuned as we're just getting started.
So there you have it: a typical weather scenario for a midcontinental location transitioning from summer warmth to winter cold.
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