The average temperature across the U.S. is a degree warmer than it was 20 years ago, and Duluth’s winters are warming rapidly, according to new data from the National Oceanic and Atmospheric Administration.

The data shows all of Duluth’s winter months warmed over the past decade, with December’s average temperature rising 2.3 degrees since 2010, January up a full degree, February up 0.3 degrees and March 1.1 degrees warmer.

December’s big warmup was the largest of any month in Duluth, but June, July and August all warmed by a degree or more and September was up 1.6 degrees.

Only April in Duluth, at 0.1 degrees cooler, didn’t see an increase.

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Overall, Duluth’s average daily temperature over the entire year increased nearly a full degree, from 39.7 to 40.6 degrees.

The data, while now part of the nation’s official forecasting system, didn’t surprise anyone who has been paying attention to the weather in recent years.

“It’s warmer pretty much across the board, except for April,’’ said Joe Moore, warning coordination meteorologist for the National Weather Service in Duluth. “December really stands out as warmer, as does September.”

The average high temperature on Christmas Day in Duluth is now 22.1 degrees with the latest 10 years of data included, up 2.2 degrees from 19.9. And on the Fourth of July the new normal high temperature in Duluth is 76.5 degrees, up from 75.1.

Duluth is seeing more snowfall as well, up more than 4 inches, from an annual average snowfall of 86.1 inches in 2010 to 90.3 inches now. The biggest snowfall increases occurred in February, April, December and May with January seeing noticeably less snow over the past decade. (January, down 2.7 inches for snowfall, appears to have given its precipitation to February, which was up 2.7 inches.)

“The big thing for me was seeing December now the snowiest month in Duluth, and that’s new. It used to be January,’’ said Pete Boulay of the Minnesota Climatology Office. December now averages 18.7 inches of snow, up from 17.7, while January dropped from 19.4 to 16.8 inches. "Temperature-wise, we all saw this coming, with warmer days and overnight lows.”

International Falls also saw a warmer December, January and September, but also had five months with cooler temperatures than a decade ago and four months with no change at all.

'Normals' adjusted every decade

NOAA adjusts its “normal’’ temperatures and precipitation every 10 years — using the most recent 30 years of data — to keep up with changing climate and to be consistent with global weather data standards. That means in most cases it takes warmer temperatures now than just a decade ago to be “warmer than normal’’ for daily forecasts.

NOAA released the new data for 1991-2020 on Tuesday, and the National Weather Service will now begin using those normals to compare daily temperatures. In short, the record keepers dropped the 1980s and added the 2010s.

The new data shows that “while the trend is warmer, we are still getting a couple weeks of deep cold in most years,’’ Moore noted. “Maybe it’s coming a little later now, into February, which didn’t warm up as much as other winter months. … As for April, we’re not sure what’s going on there to be colder.”

For the entire nation, the yearly normal temperature is now 53.3 degrees, a half-degree warmer than a decade ago and a full degree warmer than the 1971-2000 average. The new U.S. normal also is 1.3 degrees warmer than the 20th century average.

The NOAA data goes back to 1901, and the “influence of long-term global warming is obvious,” the agency noted.

Almost every place in the U.S. has warmed from the 1981 to 2010 normal to the 1991 to 2020 normal, said Michael Palecki, NOAA’s project manager, in announcing the new data.

“Changes can be subtle, depending on the region, season, and timeframe. Nonetheless, an upward shift in temperature averages is evident,’’ the agency said. Still “warming is not ubiquitous across the contiguous U.S. in either geographic space or time of year.”

For example, while nearly all of Minnesota and Wisconsin have seen noticeably warmer temperatures over the last decade, much of the Dakotas and eastern Montana have been, on average, slightly cooler.

Minnesota’s new statewide normal temperature is 41.6 degrees. That’s up 2.3 degrees from the first state 30-year normal taken from records between 1901 and 1930, the first set of 30-year normals.

Scientists say the impacts of the long-term temperature increase already are noticeable, with earlier lake ice-out dates, earlier bird migrations and increased periods of dryness interspersed with extreme rainfall and snow events. And they say the impacts are going to worsen as temperatures continue to warm.

The U.S. is growing wetter, too. The NOAA data notes the difficulty of tracking precipitation, as it varies greatly from region to region across time. Regions of the U.S. that were at least 12.5% or more wetter than the 20th-century average comprise much of the country. The Southwest, however, is getting drier.

The U.S. data is collected at nearly 15,000 stations for precipitation normals and more than 7,300 stations for temperature.