You may have heard your local TV weather forecaster say, “Today’s high was 90. That’s 5 degrees above normal.” How does that forecaster know what is considered “normal” on a given day? The National Oceanic and Atmospheric Administration’s climate normals offer an answer.
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Climate normals are 30-year averages for variables like temperature and precipitation. They provide a baseline that allows scientists to compare a location’s current or predicted weather to the average weather that location would expect to see — whether a particular day is cooler or warmer than normal, if a particular month is wetter than normal or if the growing season is longer than normal.
Who uses climate normals?
Normals are critical for characterizing current weather and climate, but they also have a wide scope of applications beyond standard weather forecasts.
For example, they help federal, state, local and tribal decision-makers plan drought responses. Climate normals can be used by farmers and gardeners to plan their crops, growing seasons and production schedules. Power and utility companies use climate normals to monitor heating and cooling degree-days when tracking energy usage.
Fluctuations in climate normals can change demand and production of oil and other commodities, potentially impacting freight capacity down the road. These deviations may affect trucking, container ship and rail capacity.
Regarding snowfall, local governments use climate normals for winter budgetary and operations planning, including plows and road salt. Knowing a location’s normal mountain snowpack is also critical for planning water resources for the warmer months.
Also, travel agencies and chambers of commerce can use climate normals for scheduling and promotional purposes.
Crunching the numbers
For the United States, NOAA’s National Center for Environmental Information (NCEI) is the official source of climate normals.
NCEI updates the climate normals every 10 years in accordance with the World Meteorological Organization (WMO). The WMO mandates that each of its member nations compute these 30-year averages and recommends an update each decade. The latest 1991 to 2020 U.S. climate normals are an update to the normals for the previous three decades, 1981 to 2010.
NOAA’s climate normals are derived from weather observations taken at approximately 15,000 federal weather stations across the country and its territories. Thousands of citizen scientists who collect local weather observations nationwide also contribute to the dataset.
It’s important to understand that NOAA’s climate normals are not simple 30-year averages. Of the 15,000 reporting stations, some occasionally have missing observations, need updated instruments or have changed locations during the last decade. Therefore, normals are complex statistical calculations that ensure they consistently and accurately represent the full 30-year climate period.
The new normals
An analysis of the updated 1991 to 2020 climate normals shows that the normals are generally warmer than 1981 to 2010 in most seasons and most regions of the U.S. Exceptions are the north-central U.S., especially in the late winter and spring, as well as much of the Southeast in November, despite October and December being warmer.
Precipitation normals across the U.S. also changed, with large increases in the Southeast and north-central states. The West has also seen distinct seasonal shifts in its precipitation patterns, while the Southwest has generally become drier.
Along with the updated climate information, the latest climate normals include several small changes regarding how they’re calculated. Also, for the first time, NOAA produced a set of 15-year climate normals (2006 to 2020) to meet the needs of specific sectors like energy and construction. In the coming months, NOAA will release detailed monthly normals data for the contiguous U.S., as well as develop new tools and methods to access the data.
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