The New Climate Normals

Every decade the National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Information updates the “Climate Normals.” The U.S. “Climate Normals” are the collection of data that provide information about typical climate conditions for thousands of locations across the United States. Normals act both as a ruler to compare today’s weather and tomorrow’s forecast, and as a predictor of conditions in the near future. The official Normals are calculated for a uniform 30 year period across the United States and the world, and consist of annual/seasonal, monthly, daily, and hourly averages and statistics of temperature, precipitation, and other climatological variables from almost 15,000 U.S. weather stations. 

The official U.S. Normals are recalculated every 10 years in keeping with the requirements of the World Meteorological Organization (WMO) and National Weather Service (NWS), and this has just been completed. The 1991–2020 U.S. Climate Normals are the latest in a series of decadal Normals first produced in the 1950s. These data allow travelers to pack the right clothes, farmers to plant the best crop varieties, and utilities to plan for seasonal energy usage as well as allow water utilities for forecast supply.  Many other important economic decisions that are made beyond the predictive range of standard weather forecasts are either based on or influenced by climate Normals.

NOAA has just released the updated set of climate “Normals.” These new normals include things like average highs, average lows, average temperature, average precipitation, and average snowfall for 15,000 locations in in the United States. The normal cover a 30 year period overlapping with the data from the previous set released in 2010. This way the new set of climate normals  evolves slowly and smoothly over time and keeps a good baseline for the climate, which will continue to change over time. 

NOAA’s normals give weather forecasters, businesses and us a 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. Two maps below show the changes in the normals from the last data group.

Temperatures change very slowly, but there seems a larger change in precipitation. The data shows that changes over the past decade and input into the series have seen an uneven change.  Even in Prince William County the change has been uneven. As you can see in the detail below, the eastern portion of the county has gotten warmer than the western portion and the precipitation has seemingly increased only in the western portion of the county. The 1991–2020 U.S. Climate Normals are the latest in a series of decadal normals first produced in the 1950s. These data allow travelers to pack the right clothes, farmers to plant the best crop varieties, and utilities to plan for seasonal energy usage. Many other important economic decisions that are made beyond the predictive range of standard weather forecasts are either based on or influenced by climate normals.

Detail from NOAA map

Detail from the NOAA map above

The U.S. Climate Normals are a large suite of data products that provide information about typical climate conditions for thousands of locations across the United States. Normals act both as a ruler to compare today’s weather and tomorrow’s forecast, and as a predictor of conditions in the near future. The official normals are calculated for a uniform 30 year period, and consist of annual/seasonal, monthly, daily, and hourly averages and statistics of temperature, precipitation, and other climatological variables from almost 15,000 U.S. weather stations. 

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 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.

Below are the monthly normals for Manassas, VA. The weather we are likely to see. An interesting note is the increase in precipitation over the period.

 

Locally, in the western portion of the county the weather has gotten a little wetter and about half a degree warmer. The data for the drought in the 1980’s was deleted and replaced with the recent wet years. So the average rainfall has increased to more than 47 inches per year. The variation in temperature is much less pronounced.