The region already has had four heat waves, and temperatures have been consistently above normal this summer, but rather than resulting in any fatalities, the heat has come in such small dosages that it might even be having a medicinal effect.

Here it is mid-July, and Thursday marked the National Weather Service's first "excessive heat warning" of 2017 for the region, according to Sarah Johnson, a lead forecaster at the Mount Holly office.

And the Philadelphia Corporation for Aging has yet to activate its "Heatline," which it does at the behest of the Health Department, said PCA's Marcia Siegal.

Finally, the city Health Department says not a single heat-related death has occurred in 2017, and this heat wave looks to be toast after Thursday. Friday's high is expected to reach a mild 82 degrees, and the 90s aren't expected to return until the middle of next week.

Officially, the temperature at Philadelphia International Airport on Thursday reached 94, with a heat index peaking at 102, before a line of thunderstorms moved through. That was the third consecutive day of 90-and-above temperatures, reaching the government threshold for "heat wave."

Why the good fortune in a city that the annual Honeywell Fans survey just ranked as the sixth "sweatiest" in the nation? (Steamier than New Orleans and Houston, but not as bad as Boston or New York.)

In short, because the city and the region have been getting huge assists from nature. So far, the heat waves have been three-and-out — none has lasted more than three days.

Health experts say it takes several days of extreme heat and hot nights to cause heat-related fatalities, especially among infants, the elderly, and other vulnerable groups.

Getting heat in short doses might even provide a measure of protection.

"There is some truth to that," Johnson said. As summer wears on and the region has more experience with heat, the weather service turns up the criteria for a "warning."

So far this summer, upper-air patterns have been progressive enough to prevent long-duration hot spells.

That is not to say that benign trend will persist.

Typically, Johnson said, those heat-producing "blocking" patterns tend not to set up until well into July and August.

And summers in general have trended warmer in the last three decades. From 1874 to 1988, the average summer temperature in Philadelphia was 74.4. From 1988, a summer when it hit 100 five times, through 2016 it was 76.7.