The weather, like so many things, just ain’t what it used to be.
Take December, for example. Back in the 1980s, the average high temperature in Madison was just over 29 degrees, and the city got about 15 inches of snow, over the course of the month. In the past decade, the average daytime high was over 34 degrees, and snowfall just two-thirds of what it was in the Reagan years. Nights were more than 7 degrees warmer.
There are even more striking differences, like an additional 8 inches of annual precipitation — the equivalent of a second spring.
But as different as it is, this new weather will soon be the new normal.
That’s because the “normal” values maintained by the National Weather Service are based on 30-year averages that get updated once a decade.
That will happen next year, when the 1980s are dropped and the 2010s added. And while the numbers aren’t final, they’re shaping up to be warmer and wetter, with some notable shifts in timing.
Jordan Gerth is an honorary fellow at UW-Madison’s Cooperative Institute for Meteorological Satellite Studies who is now helping develop the next generation of weather satellites for the National Oceanic and Atmospheric Administration.
Even though the official normals won’t be computed until next year, Gerth decided to run the numbers early to get a sense of how climate change is moving the averages.
“2020 will affect those normals ever so slightly,” Gerth said. “But the general trend is not going to change.”
Gerth, who has spent the past 14 years studying and researching atmospheric sciences, was well aware of the trend toward warmer, wetter weather, which climate scientists expect will continue in the decades to come.
“There were some things that we knew were most likely going to be in there,” he said. “But the magnitude of the amount of annual precipitation has really been quite striking.”
Over the past nine years, Madison’s average yearly precipitation was 39.78 inches, a full 8 inches more than in the 1980s. That change is likely to add more than 2.5 inches to the 30-year normals.
On average, the 2010s were 1.4 degrees warmer than the 1980s, but the change was most pronounced in low temperatures, which rose 2.4 degrees on average — and far more in some months.
There was also a surprising shift in snowfall patterns.
The 2010s had 2.1 more inches per year on average than the 1980s, but there was significantly less snow in November and December and more in January and February.
While the changes over the past decade are consistent with scientific modeling of the effects of global increases in heat-trapping gases, Gerth notes that there are other factors at play.
For example, the lack of snowfall could be a factor in the dramatic increase in December’s low temperatures: Bare ground absorbs more solar energy than snowpack, releasing that heat at night. Madison’s expanding urban footprint also plays a role. With fewer trees and more pavement to reflect the sun, cities tend to be warmer than rural areas.
Weather is variable and cyclical, which is part of the reason the National Weather Service updates its normals every decade to reflect the most recent 30 years. Timely averages are key to making good weather-related decisions, like what types of crops to grow and where, or how much insulation to use in buildings.
Given that variability, it’s difficult to determine the impact of human activity,” said Stephen Vavrus, a UW-Madison climate scientist and co-director of the Wisconsin Initiative on Climate Change Impacts.
“There is no way to know what the 2010s would have brought naturally, so we have to lean on inference,” Vavrus said.
Statewide, the 2010s were far and away the wettest decade on record, with nearly 6 inches more annual rainfall than in the previous 125 years. Climate models predict Wisconsin will become wetter as the climate warms, but not to that extent.
“I would infer that that natural variability played a big part in our waterlogged decade that just ended,” Vavrus said. “If so, then hopefully we will revert closer to average in the 2020s.”
The story with temperature is more clear.
“The 2010s were about as warm as the 2000s, both of which were the warmest decades on record,” Vavrus said. “Wisconsin’s temperature trend is consistent with the global trend, especially the consistent warming since the 1970s.”
NOAA recently announced 2019 was the second-warmest year since 1880, capping the warmest decade on record. And the five warmest years in the 1880–2019 record have all occurred since 2015, while nine of the 10 warmest years have occurred since 2005.
That will all be reflected in the next set of 30-year normals, which will nudge average temperatures and precipitation totals a little higher. While acknowledging the need for the updates, Gerth worries that the long-term pattern could be obscured.
“Just because we’ve re-established the baseline for what is normal doesn’t negate what came before,” Gerth said.
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