What ‘Normal’ Weather Is Will Change

In 2021 Weather Scientists Will Calculate Weather Patterns Over 30-Year Span

Lake Mendota with ice and open water
Lake Mendota with ice and open water. Photo courtesy of the University of Wisconsin-Madison

For all its inconsistencies weather can be reliable in certain ways. Spring is generally wet, winter cold and summer hot. We compare current temperature and precipitation to past data to see if it’s out of the ordinary.

What’s considered normal changes over time. To account for that the National Weather Service will recalculate a 30-year average of weather patterns from 1991 to 2020. The weather service does this every decade and will start next year.

The information is useful in many ways. For instance, it helps define the growing season and determines energy use.

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“Any number of those societal things,” said Jordan Gerth, a research meteorologist who recently left the University of Wisconsin-Madison to join the National Oceanic and Atmospheric Administration in Washington, D.C.

“While we do track change over time it’s good to have that baseline of that most recent 30 years,” he said.

Using a 30-year timespan helps smooth out an extreme year that may be off the charts in terms of precipitation or temperature.

Weather deviations are normal. But that normal is in a state of flux, experts say. Whether you look at data or just look outside the window you can see it.

Ed Hopkins is assistant state climatologist and has studied Madison area lakes.

“Lake Mendota finally closed on the 12th of January. It’s not the latest but obviously it’s later than the median date,” said Hopkins.

Compared to the decade from 1981 to 1990, Madison has experienced an average of eight additional inches of precipitation a year since 2011. Four of Wisconsin’s five wettest years have taken place in the last decade, Gerth said.

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