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Breakdown: Why NOAA has released new “Climate Normals”

Updated: May. 21, 2021 at 11:56 AM CDT
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MEMPHIS, Tenn. (WMC) - Every 10 years, the National Oceanic and Atmospheric Administration (NOAA) releases an analysis of U.S. weather of the past three decades that calculates average values for temperature, rainfall and other conditions.

That time has come again.

On Tuesday, May 4, the National Oceanic and Atmospheric Administration (NOAA) released the new “climate normals” for the 1991-2020 climate, marking the end of the 1981-2010 period.

The climate “normals” are 30-year averages of weather observations. A reliable estimate of an average requires at least 30 years of data.

According to the National Centers for Environmental Information (NCEI) the official normals are calculated from annual/seasonal, monthly, daily, and hourly averages and statistics of temperature, precipitation, and other climatological variables from almost 15,000 U.S. weather stations.

Simply stated: The Normals are the basis for judging how daily, monthly and annual climate conditions compare to what’s normal for a specific location in today’s climate. These Normals provide a baseline that allows everyone to compare a location’s current weather to the average weather that location would expect to see — whether a particular day’s temperature is cooler or warmer than normal, or if a particular month is wetter than normal.

In keeping with the needs and requirements from the World Meteorological Organization (WMO) and the National Weather Service (NWS), NCEI generates the official U.S. normals each decade. The last update of the normals took place in 2011, when the 30-year period shifted from 1971-2000 to 1981-2010.

What’s considered normal today is often very different from what was normal 50 or 100 years ago. The gradual adjustment of the normals is to provide context on what climate is like today, not how it’s changing over time.

There are 10 versions of the U.S. Climate Normals collection. The collection began with the 1901-1930, followed by 1911-1940 and so on through 1991-2020.

Below is a graphic that shows how annual temperatures across the country compare to the 20th-century average. The blue on the map shows temperatures cooler than the 20th-century average while red shows areas with warmer temperatures.

Annual U.S. temperature compared to the 20th-century average for each U.S. Climate Normals...
Annual U.S. temperature compared to the 20th-century average for each U.S. Climate Normals period from 1901-1930 (upper left) to 1991-2020 (lower right). Places where the normal annual temperature was 1.25 degrees or more colder than the 20th-century average are darkest blue; places where normal annual temperature was 1.25 degrees or more warmer than the 20th-century average are darkest red. Maps by NOAA Climate.gov, based on analysis by Jared Rennie, North Carolina Institute for Climate Studies/NCEI. (NOAA Climate.gov)(NOAA)

Notice how dark red the newest update is. The country as a whole has warmed 1.7 degrees Fahrenheit since the early 20th century, with a large percentage of the lower 48 warming 2-4 degrees Fahrenheit.

Scientists use the 20th-century average (1901-2000) to examine long-term climate trends. If we compare the 1991-2020 annual temperature normals to the 20th-century average, we see warming occurring across the U.S. No region is cooler in the past 30 years than it was during the 20th century.

Difference between 1901 - 1930 and 1991 - 2020 normal
Difference between 1901 - 1930 and 1991 - 2020 normal(Climate Central (climatecentral.org))

The nation’s midsection — from the Gulf of Mexico to the Great Lakes — did not warm as much as other parts of the country but saw a 5% to 15% increase in precipitation over the 20th-century average.

Normal annual U.S. precipitation as a percent of the 20th-century average for each U.S. Climate...
Normal annual U.S. precipitation as a percent of the 20th-century average for each U.S. Climate Normals period from 1901-1930 (upper left) to 1991-2020 (lower right). Places where the normal annual precipitation was 12.5 percent or more below the 20th-century average are darkest brown; places where normal annual precipitation was 12.5 percent or more wetter than the 20th-century average are darkest green. Maps by NOAA Climate.gov, based on analysis by Jared Rennie, North Carolina Institute for Climate Studies/NCEI. (NOAA Climate.gov)(NOAA)

Precipitation, of course, varies from place to place across the United States. There are only a few places that exhibit a trend either steadily wetter or steadily drier than the 20th-century average. In the image above, the green represents areas that are wetter than the 20th-century average with brown representing drier than average.

There are notable increases of precipitation across much of the Central U.S. and the Northeast between the 1991-2020 period and 1981-2000 with a drier set up across the Southwestern U.S. from 1981-2010 to 1991-2020.

While the changing pattern of temperature and precipitation may seem subtle when averaged out, these shifts result in real and expensive consequences because of an escalation in extreme weather. A NOAA analysis finds that the number of disasters each year in the U.S. that cause greater than a billion dollars in damage (adjusted for inflation) has more than quadrupled since the 1980s.

Specific to the Mid-South, below is a graphic that illustrates the difference from the 20th century average.

Ever since the 1990s, Memphis has been slighting upwards above the national average by 0.4 to 0.8 degrees.

You can see the last time the Bluff City was below the national average was between 1960 to 1990, but since then, temperatures have been going up.

Warming in the new normal
Warming in the new normal(Climate Central (climatecentral.org))

The Normals might be shifting, but NOAA scientists and forecasters say they aren’t losing track of climate change.

While putting the words “normal” and “climate” together can seem like a foreign concept these days, the new normals show us that, even in the past decade, warming was significant in most places. With each decadal update of the climate normals, temperatures keep creeping up.

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