Climate Normals

Climate Normals

 Last summer the new Climate Normals were released to the public on July 1, 2011. These Climate Normals are the latest in a string of three decade averages for the regular climatological variables (including rainfall and temperatures).  The new Normal covers 1981-2010 and replaces the previous dataset that covered 1971-2000.  This data is in raw form but is eventually broken out into more user friendly products.  The 1971-2000 products are described here.  An easy to use web breakout of the 1981-2010 products can be found here.

How do we use Normals?  Trying to remember the past weather over a 3 year period is tricky, not to mention a 30 year period.  The Normals give us “just the facts ma’am”, and supplement our memory. They give us an accurate context for understanding today’s temperature, today’s rainfall, and the other “core” Normals. Your local television meteorologist uses the Normals to compare today’s temperature and rainfall with past averages to give a more accurate perspective than relying on memory. 

 

How many weather stations contribute to the Normals? The 1981-2010 dataset included data from over 9800 stations.  Stations in different parts of the country report different data. An obvious example is that stations near Miami, FL do not report snowfall totals, but those near Minot, ND do! 

 

How many official Normals are available?  The United States started computing Normals based on a recommendation of the World Meteorological Organization (WMO).  The WMO is an agency of the UN that has a membership of 189 “Member States and Territories” .  The National Climatic Data Center (NCDC) is the producer of the official Normals for the United States. 

 

If you’d like to see a webcast (a PDF) of the release of the 1981-2010 Normals check out this link.

 

So did anything change when we updated our Normals?  Yes, there are numerous changes in the average temperatures, most of which can be seen at a glance when you view them graphically.

These images show the Statewide differences between the 1981-2010 and 1971-2000 Normals, top image is differences in Maximum Temperatures, the bottom shows Minimum Temperatures.

http://www.ncdc.noaa.gov/oa/climate/normals/img/Normals_State_Dif_Tmax_2.jpg

http://www.ncdc.noaa.gov/oa/climate/normals/img/Normals_State_Dif_Tmin_2.jpg

What do the Normals tell us about the state of the climate in the United States?  Firstly, the Normals are not developed to be a metric for measuring climate change. Secondly, based on all of the factors involved, the new Normals indicate an average temperature increase of about 0.5 degrees F.  However, these differences could be due to station moves, methodological changes, hardware (instrumentation) changes, etc. For those wanting to track differences related to climate change they need to analyze the time series maintained by the U.S. Historical Climatology Network (USHCN).  For a further detailed look at analyzing the climate and trying to determine if a change is occuring and to what degree, the US Climate Reference Network (USCRN) is in place.