In 2012, weather in southern Wisconsin, nation was hot, hot, hot

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Neil Johnson
Saturday, January 12, 2013

— The year 2012 was hot, and then some.

Consider the cloudless, grass-withering, triple-digit days of July or the warm snap in March that caused plants to green up and trees to flower weeks ahead of schedule.

As it turns out, the weather in southern Wisconsin and the nation in 2012 was the hottest on record. Janesville reached a median temperature, the average of all high and low temperatures of each month combined during the calendar year, of 51.38 degrees, according to Gazette records dating back to 1948. The next hottest year in the city was 1998, with a median 51.04 degrees.

It was the fifth time since 1948 that the median temp topped 50 degrees in the city.

The average annual U.S. temperature last year was 55.32 degrees, according to data collected by the National Climatic Data Center in Asheville, N.C.

Here are some highlights from 2012 to show just how hot it got around here:

-- In July, temperatures hit 100 degrees multiple times during a spate of dry, hot weather. The month had an average median temperature of 79.56 degrees, a full six degrees above normal, according to records. That number includes both daytime highs and nighttime lows. The last time it got even close to that hot in Rock County was in 1955, when the monthly median was 79 degrees.

-- In March, average temperatures were at least 15 degrees above normal, thanks to a number of days that saw temperatures in the 80-degree range.

The heat of March led to some weird sights in Rock County, according to Gazette reports. Spring flowers popped out the ground and unfurled at least a month ahead of time. Milton Elementary students were seen playing at recess in tank tops—and snow pants.

-- The only two months in 2012 when temperatures could be considered “normal” for the season were April and August. In those months, there were a handful of days when it was unseasonably cool—cool enough at least, to bring the months’ temperatures down to average.

It was hotter in Rock County than the rest of Wisconsin but not by much, according to data from the National Weather Service, the Federal Aviation Administration and the United States Geologic Survey. Those records date back to 1895.

The data from those three agencies, which comes from weather stations at airports and other sites statewide, shows it was the second hottest year on record in Wisconsin, said UW-Whitewater geologist John Frye.

Perhaps most telling is that records around the state were smashed multiple times last year.

“Eleven (weather) stations in the state set all-time high single day records, but four of those stations actually broke their own records multiple times this year,” Frye said. “It just kept getting hotter.”

This is not a new phenomenon, Frye said.

“Of course we know last year was a very warm year. But since 2000, most of our years have been above average for our longer-term year averages,” Frye said. “We’ve been consistently on a positive anomaly, over and above normal for our mean temperatures.”

There have been few regional studies on whether the trend could continue, Frye said. Weather experts debate the issue wildly.

But there is evidence suggesting a link between last year’s record heat and the drought conditions that destroyed crops and put much of the stateline region under government-enforced burn bans, he said.

Very warm days are typically created by high-pressure systems, which cause air to sink, Frye said. To generate clouds and rain or snow, ground level air first must rise.

“You didn’t have that happen last year,” Frye said. “These dominating ‘highs,’ when you have those in place day after day, that sinking air leads to suppression of precipitation and also warm weather continuing. There is some play between the two. It could have led to lack of rainfall.”

After temperatures Friday jumped to 50 degrees and pea-soup fog developed around the Janesville area this week, residents might be wondering if the heat of last year has again reared its head.

It’s hard to know that, Frye said, but drought conditions remain moderate at the stateline. Besides one heavy snowfall in December, precipitation has been light.

That’s a potential uh-oh, Frye said.

“If that trend continues and we don’t get a lot of snowfall, we could continue to see that drought,” he said. “It’s kind of adding on itself.”


Last updated: 8:03 am Monday, April 29, 2013

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