New 30-year climate normals introduced

Most everyone that watches a TV weathercast or follows the weather at all will hear often that the “normal high for the date is” or the “average low for today is…”  Have you ever wondered how those “normals” or “averages” are figured?

The National Weather Service publishes what are referred to as the climate normals every 10 years, based on the previous 30 year’s worth of data.  For the past 10 years, the normals have been based on the period 1971-2000. On July 1, the “new normals” for the period 1981-2010 were released and will officially start being used by the NWS on August 1.  Of course, has them for you a little early! 🙂

You can find revised climate pages for Memphis International Airport under Climate Data on, then click “Normals & Records.”  The normal highs and lows for 1981-2010, as well as the daily records have been combined into one table for each month of the year.

So what changes are there from the 1971-2000 period to the 1981-2010 period? Temperatures were, on average, slightly higher overall.  The biggest differences came in overnight lows, which rise a little more (generally speaking) than afternoon highs. The average temperature for the year rose from 62.7 degrees to 63.1 degrees, or just under a half degree. This is because the 1970s were discarded and the 2000s added, and the 21st century has so far been generally warmer than the 1970s.  The month of August was almost 1 degree warmer in the new data set, while the months of July and December were just slightly cooler.

Precipitation decreased from the 1971-2000 period to the 1981-2010 time frame by nearly 1″. The average annual precipitation for Memphis was 54.63″ in the ’70s, ’80s, and ’90s.  Removing the 1970s and adding the 2000s results in an annual precipitation total of 53.65″. Finally, snowfall also decreased fairly substantially, as the 1970s were generally colder and snowier than the 2000s. The average annual snowfall is now 3.6″, versus 4.0″ previously. Despite the decrease, the month of February is now slightly snowier than it was in the previous set of data. The biggest change was January – the average snowfall for the month dropped from 2.2″ to 1.6″. (Updated precipitation normals have not been reflected yet on, but will be within the week.)

What do you think? Do you have any anecdotal evidence to support the Memphis area getting overall warmer and drier?  Remember that one storm (or even one season) does not make a trend!

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