As mentioned in our online story, record daytime heat is likely this week. But perhaps more impressive, oppressive, will be the lack of nighttime cooling.
In the city it might not get below 70 before the sun comes up tomorrow, and the forecast low of 76 for Thursday, 76, could threaten the standing record of 78.
Warm nights are a sure sign of uncomfortable humidity; water vapor inhibits the radiation of the sun's energy into space.
Fortunately, this isn't going to be a catastrophic hot spell, and might not even meet the technical requirements of a heat wave -- three consecutive days of 90 or better.
Whether it reaches 90 today and-or on Friday will be a close call, and then the break comes Saturday.
One thing to keep an eye on is the continuing lack of rain. For the last 30 days precipitation has been well below normal throughout the region.
It's been less than 40 percent of normal in Cumberland County, and under 60 in Philadelphia.