Warmest April on record in Philadelphia … more or less

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Weather might be the only enterprise on earth that generates more statistics than Major League baseball, and the nation is fortunate to have such a treasury of publicly and readily available climate data.

Records – daily, monthly, annual – are duly noted by National Weather Service offices around the country and in the summaries published regularly by the National Centers for Environmental Information.

Yet a certain imprecision is accepted by those who keep track of those records – on both the global and local scales — and that is evident in the April temperature data for Philadelphia.

Based on the preliminary climate report from the automated thermometer at Philadelphia International Airport, the posted average April temperature was a record 59.5 degrees, besting April 1994 by the shadow of a rabbit hair, or less.

The “average” monthly temperature that appears in the climate records is the sum of the daily highs and daily lows, each divided by the number of days of the month.

Those figures are added and divided by 2, then rounded to the nearest decimal. By that measure, April 1994 came in at 59.4. But carried out to 2 decimal places, the April 2017 number was 59.45; April 1994 was 59.43.

What’s more, the daily highs and lows on the climate reports are, themselves, rounded numbers, logged with zero decimal places.

And keep in mind that the highs and lows are merely the extremes for a given 24-hour period. A more precise measure of the month would be a calculation base on the 720 hourly readings, but these folks do have other things to do.

One might reasonably ask what sane person would care whether the average for the month was 59.45 or 59.43?

For that matter, nature doesn’t care about months or 24-hour periods, so why bother keeping score at all?

In tracking changes in climate, certain human conventions have to be honored, along with certain compromises.

For example, in calculating the monthly global temperature, the National Centers for Environmental Information, uses monthly averages based on daily extremes for over 2,000 stations worldwide, says NCEI climate honcho Deke Arndt.

In computing the annual temperature, February carries the same weight as all the other months, though it is two to three days shorter.

The monthly and annual NCEI numbers are reported to 2 decimal places, but for a variety of reasons they always come with margins of errors attached, even if those margins are dutifully ignored.

In the end, those precise numbers aren’t nearly as significant as the trends.

The world has become warmer, and so has Philadelphia. All caveats aside, the average temperature in Philly has been above normal in 23 of 25 months.

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