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USA climate, the newer, higher, normals

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In July 2011, the US National National Oceanic and Atmospheric Administration‘s (NOAA) National Climatic Data Center updated the Climate Normals for the USA.These are three-decade averages of weather observations, including temperature. The new annual normal temperatures for the United States reflect a warming world.

July Maximums, 1981–2010 compared to 1971–2000 image

Following procedures set by the World Meteorological Organization, normals shift each decade, rather than each year. As of July 2011, the climate normals span 1981–2010, dropping the 1970s, which were unusually cool. Last year, the normals included 1971–2000, leaving out the warmest decade on record (2001–2010).

NASA’s Earth Observatory has provided maps which show the differences between the old normals and the new normals. The top image shows July maximum temperatures, and the lower image shows the January minimum temperatures.

Positive temperature changes appear in orange and red, and negative temperature changes appear in blue.

January Minimums, 1981–2010 compared to 1971–2000 image

On average, the contiguous United States experiences the lowest temperatures on January nights, and the highest temperatures on July days. Both January minimum temperatures and July maximum temperatures changed, but not by equal amounts.

Parts of the Great Plains, Mississippi Valley, and the Northeast experienced slightly cooler July maximums from 1981–2010 compared to 1971–2000 (top map).

A much more striking difference, however, appears in the January minimums (lower map). Nighttime temperatures in January were higher everywhere except the Southeast. Warmer nights were especially pronounced in the northern plains through the northern Rocky Mountains—several degrees warmer in some places.

Comparing average temperatures year round, every state experienced warmer temperatures in 1981–2010 compared to 1971–2000.

NOAA’s National Climatic Data Center (NCDC) released the 1981-2010 Normals on July 1, 2011. Climate Normals are the latest three-decade averages of climatological variables, including temperature and precipitation. This new product replaces the 1971-2000 Normals product. Additional Normals products; such as frost/freeze dates, growing degree days, population-weighting heating and cooling degree days, and climate division and gridded normals; will be provided in a supplemental release by the end of 2011.

Although warmer temperatures can have benefits, they pose hazards to some plants. For instance, higher nighttime temperatures enable some pests—such as the pine bark beetle and wooly adelgid—to thrive in places where they previously froze.

What are Normals? – In the strictest sense, a “normal” of a particular variable (e.g., temperature) is defined as the 30-year average. For example, the minimum temperature normal in January for a station in Chicago, Illinois, would be computed by taking the average of the 30 January values of monthly-averaged minimum temperatures from 1981 to 2010. Each of the 30 monthly values was in turn derived from averaging the daily observations of minimum temperature for the station. In practice, however, much more goes into NCDC’s Normals product than simple 30-year averages. Procedures are put in place to deal with missing and suspect data values. In addition, Normals include quantities other than averages such as degree days, probabilities, standard deviations, etc. Normals are a large suite of data products that provide users with many tools to understand typical climate conditions for thousands of locations across the United States.

What are Normals used for? – Meteorologists and climatologists regularly use Normals for placing recent climate conditions into a historical context. NOAA’s Normals are commonly seen on local weather news segments for comparisons with the day’s weather conditions. In addition to weather and climate comparisons, Normals are utilized in seemingly countless applications across a variety of sectors. These include: regulation of power companies, energy load forecasting, crop selection and planting times, construction planning, building design, and many others.

The National Climatic Data Center compiles climate normals from observations from thousands of stations in the National Weather Service (NWS) Cooperative Observer Program, as well as stations staffed by professionals within the NWS, the National Oceanic and Atmospheric Administration (NOAA), and the Federal Aviation Administration.

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