New calculations of climate "normals" indicate temperatures will be milder in January and precipitation peaks will be higher.
It may not be enough to make you cancel that midwinter trip to Arizona, but a warmer January is now "normal" for the Twin Cities.
January nights here warmed more markedly than any other part of the year in the once-a-decade update of climate "normals" by the National Oceanic and Atmospheric Administration (NOAA).
All 12 months saw an increase in the normal low temperature, but January's 3.2-degree rise was emphatic and double the next-steepest increase, according to the report released Friday. Normal highs, meanwhile, rose for nine of 12 months in the Twin Cities. January's 1.8-degree jump also led that category.
Does this mean milder winters are now normal for the Twin Cities?
"Absolutely," said Mark Seeley, University of Minnesota Extension climatologist and Minnesota climate historian.
The climate normals, by international agreement, are recalculated at the top of every decade and incorporate the most recent 30 years of weather data. They are basically averages of weather phenomena over that period, with adjustments for urban heat, relocations of observing equipment, missing data and other statistical challenges.
The "new normals" are based on weather from 1981 to 2010, and replace those that stood for the past 10 years and were based on weather from 1971 to 2000.
The figures released Friday cover about 7,500 locations across the United States and indicate what daily temperatures, rainfall and snowfall might be expected over the coming decade. Later this year, NOAA will release more detailed numbers, including day-by-day historical precipitation trends, regional climate normals and frost-freeze date normals.
For the Twin Cities, the new normal is mostly wetter and certainly warmer than what was normal from 2001 to 2010. Normal annual precipitation is now 30.6 inches, up 1.2 inches from the previous mark and the highest since the 30-year normals began in 1960.
Nationally, the new normal annual temperature is up one-half degree.
The Twin Cities' normal yearly snowfall rose a mere 0.3 inch, but a remarkable 2.2-inch increase for December masked declines in every other winter month.
Expect winter rain and ice
Extreme departures from the normals, such as last December's record 33.6 inches of snow, are always possible, meteorologist Paul Douglas noted. But the warming in January and other winter months "means a greater potential for ice and rain [in winter]," Douglas said. "It means the snow is going to be more erratic."
A longer growing season, he added, might be countered by winters that don't get cold enough to kill off insects that might wander up from more southerly homes. Seeley noted that warmer winters have already been blamed for decimating northern Minnesota's moose population.
Higher normals are ultimately no surprise, given the steady rise in monthly and annual temperatures globally and locally. Moreover, the new normals have dropped the data of the 1970s, when January low temperatures were a whopping 9.5 degrees colder than they were in 2001-2010, according to Anthony Arguez, who has overseen the recalculation of climate standards for the National Climatic Data Center.
Even though January will still have the coldest normal low temperature of the year in the Twin Cities, Arguez said the 3.2-degree rise from the last set of normals "raised my eyebrow."
Warming winters across the Northern Hemisphere, particularly warming winter nights, have been a key feature of ongoing global warming. Jim Hurrell, senior scientist in climate and global dynamics for the National Center for Atmospheric Research, said that in recent years a phenomenon known as the Arctic Oscillation has amplified the warming effects of increased greenhouse gases. The oscillation, he said, has been reverting repeatedly to a phase that has allowed warmer, maritime air to flow more frequently across northern latitudes.
Climate normals are most often used by the media and other weather-watchers to put weather events in context. Historically they've also been used for planning in agriculture, energy and other industries. But that appears to be less the case today, in part because the climate is changing so rapidly. Xcel Energy, for example, now uses 20-year normals as its standard. The National Climate Data Center is considering different ways of calculating normals, as well.
Seeley added that the new normals may also tend to dull people's sense of the pace of climate change, by presenting a static picture based on a 10-year increment.
"If we go back in climate history, holy cow, are we warmer than we were decades ago," he said. "Climate is changing at a pace that's more dramatic than what we've experienced. What validity does the 30-year period have anymore?"
Bill McAuliffe • 612-673-7646