Weather: Striving For Average
What is "normal" when it comes to temperatures really isn't—it's an average. Phillyweather.net's Tom Thunstrom explains the highs and lows of average temperatures in this week's withering of weather.
For weather geeks, this time of the decade is like a World Cup and Olympics wrapped into one.
It's the time when the National Oceanic and Atomspheric Administration comes out with new average high and low temperatures for the thousands of climate sites throughout the United States. You probably have heard of these referred to as "normals." However, there really isn't anything "normal" about them.
Average temperatures are based on a 30-year period of time, with the newest averages based on 1981-2010's temperatures. The daily highs and lows for each day in that 30-year period are added up and divided by 30 to get a rough average temperature. Since the average from day-to-day can vary, climatologists take the rough average and smooth it out, providing you "normal" highs and lows on a daily basis that climb steadily from late January to July and fall from the end of July to January.
The averages of each day in a month (highs and lows) are taken together to provide a monthly average temperature, which is used to get a sense of how much warmer or colder to "typical" we are.
From our last average period (1971-2000) to the current average period, Philadelphia's average temperature climbed by a half a degree, with the largest climbs taking place in February, April and June (see the graphic for more detail).
Some of the larger change is due to some downright cold Februaries in the 1970's falling off the average list (February 1978 and 1979 were both among the coldest on record back when "ice age" hysteria was all the hype in some circles), while April's spike was due to our recent run of rather warm Aprils the last few years.
Switching from cold thoughts to summer heat, this week's weather is definitely "typical" as far as summertime weather. Expect daily high temperatures near 90 for much of the week, with thunderstorms possible in the afternoon on Thursday and perhaps lingering into Friday as a weak front tries to work into the region and gets stuck nearby. One can say this week will be striving for "average" as far as what is considered normal summer weather.