Meg Jones, Milwaukee Journal Sentinel
Weather normals will soon change in Wisconsin.
And that means the new normal will be different than the old norm — wetter with less early winter snow and warmer summer nights.
The National Weather Service uses 30 years of data to establish a pattern to compare forecasts and extreme weather. Currently, the weather service is using data from 1981 to 2010.
But starting Jan. 1, that will switch to data between 1991 and 2020, swapping out the 1980s for the most recent decade.
"What we saw from 2011 to 2019 is a fairly marked increase in precipitation and night-time low temperatures," said research meteorologist Jordan Gerth, who analyzed changes in Madison's average climate.
Last year was the soggiest year for both Wisconsin and the entire contiguous U.S. dating to 1895. In fact, four of Wisconsin's five wettest years happened during the last decade.
Overnight low temperatures have risen, particularly from May through December. On average, December has been 6 degrees warmer since 2011 than during the 1980s.
Though it's too early to use 2020 weather statistics, Gerth's analysis shows the 30-year average low temperature for December will likely rise about 2 degrees from the previous average.
"We were really surprised more than anything to see a bit of a shifting of the seasons. That was really evident with September tending to be warmer and December tending to be quite a bit warmer," said Gerth, who has an honorary fellowship at the University of Wisconsin-Madison and works for the National Oceanic and Atmospheric Administration in Washington, D.C.
That will likely affect farmers since growing seasons are lengthening in Wisconsin and that boosts crop yields. It's likely affecting animals ranging from mosquitoes to white-tailed deer. And it will likely affect energy use in the state with air conditioning usage growing because of more warmth in the summer and less heating costs in the winter.
"Any living creature that has some sort of season dependence on its life cycle will feel this impact," said Gerth.
Meanwhile, seven consecutive years of above-normal precipitation and flooding have boosted high water levels across Wisconsin and the Great Lakes.
Last year was the wettest year in Wisconsin dating back 125 years with more than 41 inches of liquid-equivalent precipitation. That includes measurements of melted snow.
Analyzing Madison's climate data, Gerth discovered the city has averaged 8 more inches of precipitation annually since 2011 compared to the 1980s. Plus the average duration of ice on Lake Mendota in Madison has shrunk by about three weeks since records started in the late 1800s.
The lake froze this season on Jan. 12, 2020. The latest Lake Mendota has ever closed was on Jan. 30, 1932.
Madison has gained more than 30 frost-free days since 1971. And Gerth noted that although warmer Novembers and Decembers have meant less snow, the shortage has been made up by heavier snows in January and February. That has translated into an average of 2 additional inches of snow falling in Madison since 2011 compared to the 1980s.
Using three decades of weather statistics dates back to the 1930s, said Wisconsin State Climatologist Ed Hopkins.
Forecasters and scientists "started to notice there's some change in the climate. They tried to figure out how many years to give a relatively stable number for the average. They argued and felt that if you take averages of 30 years of numbers, it's better," Hopkins said.
"They also felt it would be a little bit too long if you wanted to use 50 years, probably because there wasn't a lot of stations (back then) that had good records dating back that long," said Hopkins.