Decadal update from NCEI gives forecasters and public latest averages for 1991–2020
NOAA’s new U.S. Climate Normals give the public, weather forecasters, and businesses a standard way to compare today’s conditions to 30-year averages. Temperature and precipitation averages and statistics are calculated every decade so we can put today’s weather into proper context and make better climate-related decisions.
Normals may be familiar to most Americans by their inclusion in local daily weather information from television, radio, print, and digital media. Not only do Normals indicate how conditions measure up for the nation as a whole, but also for specific locations—from Bangor, Maine, to San Diego, California. And, from Nome, Alaska, to San Juan, Puerto Rico.
U.S. Climate Normals are designed—and best-suited for—better understanding what is happening today. Rather than assess long-term climate trends, Normals reflect the impacts of the changing climate on our day-to-day weather experience. Normals are not merely averages of raw data. Thirty years of U.S. weather station observations are compiled, checked for quality, compared to surrounding stations, filled in for missing periods, and used to calculate not only averages, but many other measures. These then provide a basis for comparisons of temperature, precipitation, and other variables to today’s observations.
Supplemental Normals for the 15-year period 2006–20 are being released simultaneously with conventional 30-year Normals for users who require information for periods closer to the present.
Why Update U.S. Climate Normals?
Member states of the World Meteorological Organization (WMO) are required to calculate their country’s normals at ten-year intervals. Countries follow recommendations by the WMO, which provides a framework for international cooperation among meteorologists, climatologists, and hydrologists.
The decadal update is the equivalent of the Census for those who use the data. It replaces the previous set of U.S. Normals, which cover all 50 states and U.S. territories such as Puerto Rico and Guam. NCEI and its predecessors have been the official source for U.S. Climate Normals since the 1950s. New data come from approximately 8,700 National Weather Service stations operated by NOAA, which include Automated System Observing Stations (ASOS) and Cooperative Observer Program (COOP) stations.
For the first time, Precipitation Normals have been created for more than 770 Snow Telemetry (SNOTEL) stations managed by the U.S. Department of Agriculture and for more than 5,400 citizen science observation stations from the Community Collaborative Rain, Hail, and Snow (CoCoRaHS) Network. Calculating and making available the new averages is a significant undertaking that requires months of preparation by a team of climate scientists, including NCEI partners from the Cooperative Institute for Satellite Earth System Studies (CISESS) and NOAA Regional Climate Centers (RCCs).
Normals provide information about national and localized average temperature and precipitation as well as other parameters, such as snowfall, heating and cooling degree days, frost and freeze dates, and growing degree days. Several new Normals will be introduced for the first time, including Seasonal Normals representative of different states of the El Niño/Southern Oscillation (ENSO) and High-resolution Gridded Normals, which are data that represent Climate Normals at 5 km intervals north and south across the contiguous U.S. to allow for easier calculations and mapping of climate averages and departures from normal. New Normals access tools will also be forthcoming from our RCC partners.
By comparing averages to weather observations, anyone interested in the conditions at specific locations can learn whether a variable is above, below, or near average. For instance, the average temperature during the February 2021 Arctic air cold outbreak in the Dallas–Fort Worth area was 42°F below normal on February 16, according to the 1991–2010 Normals.
Along with the National Weather Service (NWS) and meteorologists and forecasters in the private sector, the new Normals impact the work of numerous public and private stakeholders, including the energy and agricultural sectors of the American economy, building design, infrastructure, construction, and several governmental organizations, such as the USDA.
Changes Since 1981–2010 Climate Normals
As anticipated, changes have occurred in averages since the last ten-year update. Since two-thirds of the data (1991–2010) in the new set overlap with the previous version, changes can be subtle, depending on the region, season, and timeframe. Nonetheless, an upward shift in temperature averages is evident. The 1981–2010 average temperature for the contiguous U.S. was 52.8°F while the new average temperature for the contiguous U.S. for 1991-2020 is 53.3°F. The new normals period, 1991-2020, is the warmest on record for the country. But warming is not ubiquitous across the contiguous U.S. in either geographic space or time of year. Changes vary from season-to-season and month-to-month.
For instance, the north-central U.S. Temperature Normals—for those in the Northern Plains and Upper Midwest—have cooled from 1981–2010 to 1991–2020, especially in the spring. The South and Southwest are considerably warmer. Normals were also generally warmer across the West and along the East Coast. Precipitation-wise, the Southwest was drier; wetter averages emerged in the U.S. east of the Rocky Mountains, especially the Southeast in the spring.
In the transition to the new set of Normals, shifts in the relative frequency of above- and below-normal conditions will occur. Shifts will be most discernible in areas of the country undergoing substantial warming in the last decade, as experienced in the West and Florida. In those cases, comparisons of averages to current conditions will trigger below-normal temperature days more frequently. This does not mean that conditions are “colder” in the absolute sense; in actuality, higher averages have raised the bar for warmth.
Climate Normals and Climate Change
Rather than track or define long-term trends or changes in climate, U.S. Normals are useful to understand present-day conditions. For climate monitoring activities at NCEI, longer periods are referenced. The monthly State of the Climate reports produced for the United States and globe use twentieth-century averages (1901–2000) as benchmarks and will continue to do so. The yearly Bulletin of the American Meteorological Society State of the Climate report also relies on longer periods of record.
Several reasons underlie the use of the twentieth-century averages for climate change monitoring:
- The 1901–2000 baseline offers more consistency as conditions change over time and is not subject to updates every 10 years.
- The period is an easy-to-understand range when discussing long-term climate change with non-technical audiences.
However, long-term trends from decade to decade can affect baseline “normal” weather conditions. For instance, the last decade includes the warmest seven years on record for the globe, according to NCEI.
Additional products and services will be released later in 2021 and into 2022, including Daily Gridded Temperature and Precipitation Normals. Plans are also underway for NOAA NCEI to become a repository for climate normals from countries around the world.