Every 10 years climate averages, called “normals” are calculated and then used by weather service offices across the U.S. These numbers are then integrated into consumer climate products through every National Weather Service Office webpage and displayed on almanac pages at local TV stations, such as here at ABC7 during each newscast. These averages are compiled from 30 years of consecutive weather data.
The current climate normals are based on the 1971 to 2000 time period and were released in 2001. Prior to this, the numbers were crunched from the 1961 to 1990 period. Climate normals first started in 1956 after the 1921 to 1950 period.
The freshest 30-year period of 1981 to 2010 normals were published by the National Climate Data Center in Asheville, N.C., earlier this month. Starting on Monday, August 1, 2011, each National Weather Service office across the U.S. will begin using these updated climate normals in daily operation. Therefore, average yearly, monthly and daily highs and lows and precipitation will be updated by our local National Weather Service in Sterling, Va., at the start of the new work week.
When comparing the 1971 to 2000 normals with the fresh 1981 to 2010 normals for Reagan National Airport that will be released Monday (numbers listed are in degrees Fahrenheit), average temperatures for each month of the year have increased, with the most significant change noted in January:
|January: +1.1 degrees||Feb: +0.9 degrees||Mar: +0.3 degrees||April: +0.7 degrees||May: +0.4 degrees||June: +0.6 degrees|
|July: +0.6 degrees||August: +0.7 degrees||Sept: +0.5 degrees||Oct: +0.7 degrees||Nov: +0.9 degrees||Dec: +0.2 degrees|
There are a few important weather events that could have skewed the numbers for this new set of normals in the Washington/Baltimore area.
June to August 2010 was the warmest on record for Washington, D.C., and Baltimore. 1988 tied for the most number of days at or above 90 degrees at Reagan National while Baltimore was just one day shy of the most number of 90 degree days in 2010.
Dulles International had its snowiest month ever in February 2010 when 46.1 inches accumulated. Washington, D.C., had 11.5 inches of snow in November 1987, the most ever for that month while December 2009 was the snowiest for Reagan National with 16.6 inches. In addition, 23.8 inches of snow made January 1996 the fourth snowiest January on record in Washington, D.C.
There are a few important national highlights that have impacted this set of fresh normals. The U.S. had its fourth warmest summer on record in 2010 while the summer of 2006 was the second warmest in recorded history. April 2010 was the 14th warmest while the Southeast and Northeast had their warmest May through July period in 2010.
NOAA’s preliminary indications show 1981 to 2010 had a modest warming trend when compared to the current 1971 to 2000 climate normals. Statewide averages for highs and lows are warmer across the board (as seen with Reagan National's numbers in the list above) and normal temperatures are warmer for every month of the year in general across the U.S. with January seeing the largest increase. Temperatures in January are, in general, 1.7 degrees warmer in the U.S. with the 1981 to 2010 normals.