Warm autumns: They're growing on us

When the temperature reached 32 at 2:30 a.m. Sunday at Philadelphia International Airport, it ended a 245-day stretch in which the official reading failed to hit the freezing mark.

We've mentioned that this represented the longest wait for a 32 reading in 71 years in Philadelphia, and those 245 days represented the 10th-longest interval between freezes in the 137 years of recordkeeping.

The so-called growing season evidently has grown considerably in the last 30 years.

In the first decade of the millenium, on average 229 days passed between the last official freezing reading of spring and the first of the autumn. That's a full four weeks longer than the figure for the 1960s.

In 2010, the last spring freeze occurred on March 28. On average, in the last decade, it occurred on March 31. In the 1960s, April 7.

The autumnal change has been far more dramatic.The first freeze of autumn was showing up on Oct. 25 in the 1960s, on average; Nov. 14 in the last decade.  

A word of caution about reading too much into this: Data can be the enemy of perception as surely as information can be the enemy of certainty.

In the first decade of the 19th Century and in the 1930s the average space between official freezes was two days longer than its 20th Century counterpart.

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