New US climate normals are arriving soon

A new kind of normal that will influence decisions across many sectors of the nation’s economy is on the horizon: the new U.S. Climate Normals. Within the National Oceanic and Atmospheric Administration (NOAA), the National Centers for Environmental Information, where I work, publishes the official Climate Normals for the United States, and we are releasing the 1991-2020 U.S. Climate Normals in early May 2021.

At their core, climate normals are 30-year averages of weather observations — like temperature or precipitation — and the statistics behind them. Normals are not just simple averages, thus the different name. Observation records for some weather stations may be incomplete or have other issues, and NOAA uses science-proven procedures to correct the data used to calculate normals.

Normals are critical for characterizing today’s climate. They provide a baseline that lets us know whether a particular day is colder- or warmer-than-normal, or if a particular month is wetter-than-normal, or if the growing season is longer-than-normal. It allows travelers to pack the right clothes, farmers to plant the best crops and electrical utilities to predict seasonal energy usage — along with other important economic decisions beyond the range of standard weather forecasts.

At NOAA, these 30-year, or “conventional” Climate Normals, are updated only once every 10 years (after a year ending in “0”) in accordance with the standards set by the U.N. World Meteorological Organization.

So, what do the new 1991-2020 normals tell us?

Most of the contiguous U.S. was warmer, and the eastern two-thirds of the U.S. was wetter, during 1991-2020 than during the previous normals period, 1981-2010. Since 20 years of both periods overlap (1991-2010), the changes are perhaps more muted than expected. However, examining individual months shows much more dynamic changes. For example, the new normals are cooler in the spring in the north-central U.S.; while much of the Southeast is now cooler in November, despite October and December being warmer.

What about climate change? Does changing the normals mean we are “moving the goalpost,” or “raising the bar,” to mitigate the effects of climate change?

No. It’s true that the warmer 1991-2020 normals may lead to a few additional cases of temperatures falling below the new threshold when we start using those normals. However, this is why normals are routinely updated every 10 years. We want to give the best estimate for today’s climate. This is the dual nature of climate normals, being a ruler to measure against and a seer to predict the near future. Additionally, normals provide us with a window to see climate change in action, to measure its effects, and to adjust our decision-making today.

To examine long-term climate change, NOAA uses a more lengthy timeline — the 20th-century average (1901-2000). If we compare the 1991-2020 annual temperature normals to the 20th-century average, we see ubiquitous warming across the map. No region in the U.S. is cooler than it was during the 20th century, and much of the West and Northeast are one to 2 degrees warmer. The nation’s midsection — from the Gulf of Mexico to the Great Lakes — did not warm as much due to a 5 percent to 15 percent increase in precipitation over the 20th-century average.

So, when you see your local TV weathercaster get excited talking about how above or below normal tomorrow’s weather will be, all of these individual daily records are also telling the story of U.S. climate change, incrementally, day-by-day and, decade-by-decade. This “new normal” will look and feel different than the climate we have been used to, and certainly the climate during the decade when you were born.

Michael A. Palecki, Ph.D., is a physical scientist for NOAA’s National Centers for Environmental Information in Asheville, North Carolina. He is the project manager for the 1991-2020 U.S. Climate Normals. He has worked on projects ranging from the validation and use of climate measurements taken in the mid-19th century to studying today’s climate using the NOAA U.S. Climate Reference Network.