When you see the average high or low temperature or average snowfall and rainfall, do you know how that number gets derived? Did you realize it gets updated every so often, too?
These numbers are called climate normals and they are updated every 10 years. Each set of normals are calculated based on 30 years of weather data. For instance, the current temperature averages are based on 30 year averages from 1971 to 2000. The previous climate normals included all years from 1961 to 1990, etc.
Climate normals first came into existence in 1956 after the numbers were crunched from the 1921-1950 period. Every 10 years these numbers get updated. On July 1, NOAA will release the new averages, which are based on the next set of 30 year averages....1981 to 2010.
Statewide averages of annual normals of high and low temperatures show that the 1981-2010 normals are warmer than the 1971-2000 for all lower 48 states. In addition, low and high temperatures are warmer for each month of the year in the lower 48, especially January. Preliminary results show average high temperatures in July are 1 to 1.5 degrees warmer in the Mid-Atlantic with the new set of climate normals compared to the current numbers.
Specifically, for Reagan National, Dulles International and BWI Airports, the National Weather Service in Sterling, Va., plans to release the new climate normals for these stations next month as well. A specific date has not yet been set.
In order for a weather station's data to be considered in the calculation of climate normals, it must have 2 years of complete weather data with no erroneous data and must have reported at least one value in 2010.
Have a great weekend!