New 1991-2020 Climate Normals

New NOAA Climate Normals

NOAA uses a 30 year period to calculate "normals" for temperatures, rainfall, snowfall, and other climate variables. These normals are useful to compare one location with another, and to compare daily, monthly, or yearly weather at a single location to what typically occurs. Since climate is not static and changes over time, we recalculate normals every ten years.

The period 1981 through 2010 has been used over the past decade, however beginning Tuesday, May 4 we will begin to use the new period 1991 through 2020.

New 1991-2020 Climate Normals and comparisons with the old normals are available here:

For Wilmington, Lumberton, Florence, and North Myrtle Beach, new normal 1991-2020 annual, monthly, and daily temperatures, rainfall, and snowfall are found in the left columns. The center columns show the old 1981-2010 normals which are no longer used. The right columns show the difference between the new normals and old normals. Positive values indicate the new normals are warmer or wetter; negative values indicate the new normals are cooler or drier.

Across the eastern Carolinas most long-term climate stations have experienced around a half degree Fahrenheit increase in average temperature since the last time climate normals were updated in 2010. The increase in nighttime low temperature has been larger than the increase in daytime high temperature. The increase in normal temperature shows up in every month of the year except for November where temperatures have decreased slightly.

Wilmington, NC change in monthly average temperature from the old 1981-2010 normals to the new 1991-2020 normals

Changes in rainfall have been smaller in magnitude and have not all been in the same direction. Wilmington and Florence's normal rainfall has increased slightly, while normal rainfall in Lumberton and North Myrtle Beach has decreased. Across the eastern United States most stations have seen increases in normal annual rainfall with this new update. Wilmington's normal annual rainfall now exceeds 60 inches for the first time since this statistic has been calculated.

Changes in normal annual rainfall (inches) from 1981-2010 to 1991-2020

Average annual snowfall in Wilmington has decreased by almost 50 percent and is now only 0.9 inch per year. The biggest reason for this substantial decrease is the lack of recent snowy winters, and the fact the Christmas 1989 snowstorm is no longer part of the 30 year period (1991-2020) used to calculate climate normals. This is the smallest 30 year normal snowfall since it has been tracked in Wilmington.

Wilmington snowfall annual totals and 30-year climate normals

Frequently Asked Questions

Why are climate normals recalculated every ten years?

The new normals better characterize the climate we experience here in the Carolinas today rather than the climate that was experienced 30, 50, or 100 years ago. Climate changes due to both manmade and natural factors, and these new normals help keep pace with continuing changes.

Why do we use a 30 year period to create climate normals?

Since the 1930s the World Meteorological Organization (WMO) and its predecessor organizations have promoted a 30 year averaging standard. This period is usually long enough to smooth out the impact from a single weather event or an unusual year while preserving the important seasonal and local variations that define a region's climate. The official guidelines set by the WMO are explained here: https://library.wmo.int/doc_num.php?explnum_id=4166

Are there normals calculated for periods other than 30 years?

Later this year NOAA will release an alternative set of normals for the 15 year period 2006 to 2020. In some regions the climate is changing so quickly a shorter period of record is more appropriate to compare day to day observed weather with what is considered normal.

Who uses NOAA's climate normals?

Farmers use climate normals to help determine crop selection and planting times. Power companies use normals to help predict demand for energy used in heating and cooling. Engineers and architects use normals in construction and building design. And of course meteorologists and climatologists in both the public and private sectors use these normals in their studies and forecasts.

Additional Links

U.S. Climate Normals 1991-2020 for thousands of U.S. Stations: NCEI

NOAA 1991-2020 U.S. Normals: 16 minute video presentation by Michael Palecki, NOAA NCEI

NOAA is updating its Climate Normals; Why it Matters: NOAA NESDIS news

Climate change and the 1991-2020 U.S. Climate Normals: Rebecca Lindsey, NOAA Climate Office

Page Author: Tim Armstrong
Last updated: May 4, 2021