As we reported on (today's promo code is N38A), today is going to set a daily record for overnight warmth with a low temperature that reads more like a high -- 81.

The record-high minimum for a July 19 is 78. Tony Gigi at the National Weather Service iin Mount Holly would be apt to call this a "cheap record" since in a sense it's low-hanging fruit.

The record for a July 15 is 81; it's 80 on the 16th, and 80 on the 18th. What that suggests to us is that we haven't seen all the weather there is.

Overall,  Western Civilization has done a fabulous job of writing things down, and the U.S. climate record is a national treasure.

Philadelphia has one of the nation's oldest official climate databases, dating to 1872 and the beginnings of the national weather observing network.

Yet scanning daily records, we see that the daily low and high records don't follow a linear pattern. As you can see on this chart, for example, the record high for a July 15 is 103, and for tomorrow, its 99.

A case can be made that the record set will keep going onward and upward, assuming background worldwide warming continues.

However, we would make the case that the daily records would have a far-more linear look if the record dated to, say, 250, or 300 years ago.

Aside from the length of the climate records, we also should note that our official data is flawed, something that climatolgists fret over mightily. When the folks at the National Climate Data Center work up their global temperature calculations, this is a reality that they take into account.

In Philadelphia, for example, a low of 82 was recorded during the centennial year, 1876, when the official Philadelphia station was at 505 Chestnut Street.

More 82s showed up when the station was at 10th and Chestnut. Measurements moved to the airport in 1940, and during the 1980s, the official thermometer was known to run hot.

In 1995, the thermometer technology changed to that of an automated observer, and the temperature readings were moved to an airport meadow, which is near a swamp and the confluence of the Delaware River and Schuylkill.

Jim Eberwine, now retired from the weather service, is convinced that the thermometer is subject to micro-climate effects from the proximity of the water, making it susceptible to mini-sea breezes.

That might explain why a record for a high minimum was tied on Tuesday, rather than broken. The standard for a July 16 is 80.

After a toast overnight, at 10 p.m. Tuesday the reading had not got below 90, but at 11:51 p.m., it dropped precipitously to 80.