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Dry run

If it happens, rain would break a significant dry spell.

After setting a precipitation record for February and March, the mud has dried out, the first traces of dust are appearing and the region has slipped quietly into a rain deficit.

In the last 60 days rainfall in Philadelphia is about two-thirds of normal, and is below normal in every county in the region. Those hit-and-miss thunderstorms have been mostly miss.

In February and March close to 13 inches of precipitation was measured officially at Philadelphia International Airport, with less than half of that since.

The dryness may have contributed to the modest five-day heat wave that ended yesterday. The Earth acts as a giant radiator, and when the ground is moist, some of the sun's warming energy gets diverted to evaporating water.

Significant rain is expected tomorrow and tomorrow night, perhaps an inch or so and delay any onset of drought conditions.

The region has been on a rain roll for the last several years. Pennsylvania hasn't had to issue a drought advisory for the region since 2002; that's the longest drought-free period since the state started keeping score back in 1980.