At 2 p.m., the relative humidity in Philadelphia was a bone-drying 19 percent, closer to what one expect in the Mojave rather than in a place so close to major bodies of water.
Combined with the winds, and stubbornly bare trees that are allowing the sun to dry out surfaces, conditions have been ripe for brush fires.
That's about to change.
Humidities are due to build back up this afternoon, and some decent rains are expected after dark, perhaps a half inch or so as a storm cross the region from the Ohio Valley.
Then quite a wet pattern is forecast to set up next week, with rain possible at times Tuesday through Thursday.
So far this month rainfall has been about half of normal in Philadelphia, and elsewhere this has been an amazingly quiet period for severe weather. The two evidently are related.
The nation's tornado numbers so far are way, way down, perhaps at record low levels, and not a single EF3, a twister with winds of at least 138 m.p.h. capable of tossing a mobile home, has been reported.
According to the Storm Prediction Center, in Norman, Okla., only 39 tornados were reported this month as of yesterday; the April average in the previous three years was 350.
One factor has been cooler-than-normal sea-surface temperatures in the northwest Gulf of Mexico, said Dan Kottlowski, a meteorologist with AccuWeather.
In addition, he said, the tendency of those high-speed jet stream winds from the west to dive deeply in the United States has resulted in surges of dry air, such as the dryness experienced around here the last few days.
But the severe-weather season also is about to change – for the worse, said Kottlowski. The most violent tornado outbreak of the season is due this weekend, targeting areas such as northern Texas and Kansas.