Heat deferred

After four consecutive months of below-normal readings, May temperatures in Philadelphia are averaging slightly above normal.

But the region hasn’t experienced any serious heat yet, and none is in the longer-term outlooks. The government's  latest two-week outlook sees temperatures about where they should be.

The official temperature in Philadelphia peaked at 88 on Tuesday, and that’s as high as it got in May.

By day's end tomorrow, this will mark the first time since 2008 that the temperature failed to hit 90 before June 1, and only the second time in the last decade.

In the 142-year period of record, the average date for the first 90-degree reading is May 28, but in the 30-year “normal” period – 1981-2010 – the date was May 23.

Since the government has been keeping score, the official temperature in Philadelphia has reached at least 90 in all 142 years, but the first occurrence of 90 has been subject to considerable decadal variability.

From 1985 to 1994, the average date was May 14; from 1875 to 1884, it was June 9. From 2004 to 2013, it was May 26.

The earliest 90-degree reading in Philadelphia occurred on April 7, 1929; the longest wait for a 90 reading was in 1972, when it didn’t happen until July 14.