You often hear the Channel 7 weather team talk about the averages for the day but do you realize how rare it is to nail the averages on the nose on any given day? We can come close in a mundane weather pattern but Sunday proved to be the winner of them all; the averages were hit dead on!
This screen capture below of the ABC7 Almanac says it all! Guess what… the temperature was perfectly in line with the averages of 67 and 49 degrees on Sunday!
So with that in mind, how is an average temperature determined? Well, first of all, consider this; it’s recalculated once every 10 years, based on 30 years of data. This is the requirement from the World Meteorological Organization.
The set of “normals” or averages were released in 1956. The temperatures calculated in this first set of “normals” were based on weather data collected from 1921 through 1950. They were updated every decade thereafter. So, the next set was 1931-1960, then 1941-1970, 1951-1980, 1961-1990, 1971-2000 and the current set of averages are based on weather data from 1981-2010.
The average high and low for any given day of the year is computed by averaging the high temperature for the 30 consecutive years of data (in Sunday’s case….the high temperature on October 21st in 1980, 1981…etc., to 2010) and then dividing by 30…which is the number of years for which the high temperature is being extracted... and you end up with the average high temperature. The same computation is done with the low temperature.
The record high and low temperature for any given day is simply the hottest or coldest day at that weather station (Reagan National Airport in Washington, for instance) since weather records began.
Going forward, the average high and low temperatures will continue to get colder as the days get shorter, reaching the coldest for the calendar year between January 2nd and the 22nd when the average high is 43 and the low is 28-29 degrees. The climatologically warmest days of the year occur between July 7th and the 22nd when the average high is 89 degrees and low is 71 degrees.
(Courtesy: NWS in Sterling, Va.)
Speaking of averages, the thermometer will shoot well-above average later this week as high pressure moves off the coast and southwest winds usher in warmer weather! As a matter of fact, Reagan National Airport will challenge record highs Tuesday, Wednesday and Thursday. Records in jeopardy include the following: 85 degrees for Tuesday, 84 set in 2001 for Wednesday and 80 in 1902 for Thursday.
Enjoy because cooler changes are waiting in the wings late in the weekend and early the following week!