The ancient Greeks and Romans called the steamy days of late summer "dog days," in the misguided belief that the appearance of Sirius, the Dog Star, added to the sun's heat.
Today, meteorologists have a more accurate explanation for why it routinely becomes oppressive this time of year: They call it August.
"It happens every year," said Lee Robertson, a meteorologist with the National Weather Service office in Mount Holly.
If anything, the recent heat and soup-thick air feel inordinately uncomfortable because we've become spoiled.
To the surprise of meteorologists who had called for a hot summer, it has been mostly benign, with temperatures averaging close to normal.
Philadelphia has recorded only two heat-related deaths this season, both in July, said Jeff Moran, spokesman for the city's Department of Public Health. When it's been hot, the heat wave hasn't lasted long, and it is lingering high temperatures that drive up death tolls.
The season's longest stretch of 90-plus days ended at an unimpressive five on Monday, when the temperature topped out at 86. The government defines a heat wave as three consecutive days of 90-degree temps, so by that definition, we've only had two, the first coming July 8 through 10.
An excessive-heat warning is in effect today, with an expected high in the mid-90s, but the hot spell should end tomorrow. Not that it has been a memorable one.
Sabotaged by afternoon cloud cover, the result of thunderstorms well north of the region, yesterday never lived up to forecasters' dire warnings. The city's official high of 92 was 14 degrees short of the record for the date.
That 106 reading was set back in 1918 on a day when the Phillies fell to the Pittsburgh Pirates, 4-2, in North Philadelphia's old Baker Bowl. It remains the warmest day in Philadelphia since record-keeping began in 1873.
So far this summer, the temperature at Philadelphia International Airport has yet to top 96, and June and July were almost abnormally normal in the region.
Those months were characterized by generally higher pressure in the upper atmosphere in the West and lower pressure over the East, said Mike Halpert, a long-range forecaster for the government's Climate Prediction Center.
High pressure, or heavier air, favors warm and dry conditions, and the opposite is true of lower pressure. The heat finally pushed eastward last week, but tomorrow will be back in the upper 80s and the summer of 2007 should return to its seasonable ways by Friday.
In short, we don't have much to complain about. If you start sweating, think about all those suffering people back in 1918. With the production demands of World War I, the region's steel, shipbuilding and textile plants hummed relentlessly, said Roger Horowitz, researcher at the Hagley Museum and Library, the industrial museum in Wilmington.
"A lot of heat was coming off those machines," he said. "You probably had 115 to 120 degrees in those factories."
On Aug. 7, 1918, the lucky ones were working outside, where it was only 106.