May Marches in

This will end at some point, but as far as computer models can see with any degree of clarity, that point remains elusive.

"It is a broken record," Tony Gigi, meteorologist at the National Weather Service office in Mount Holly wrote in today's forecast discussion.

"We see no end to the unseasonably mild weather in the long term."

Just how unseasonable is "unseasonably?"

The high today at Philadelphia International Airport, 74, is the normal high for May 18.

The persistency of the winter-long warmth has been extraordinary, and it's related to the North Atlantic Oscillation, which has been pretty much locked into its warm phase since September.

We'll spare you the treatise and just note that it is tracked by an index of air pressure at stations near Greenland and Portugal.

When it's higher in Greenland, the index is said to be "negative," and cold air can migrate into the northeastern United States. For our purposes, that would be the cold phase.

The reverse is true when the pressure is higher near Portugal, and the index is "positive."

As you can see from the monthly index, the readings have been positive for the last six months. 

More impressively, however, is the fact that it was negative every month from June 2009 to January 2011, and, yes, that period coincided with four 15-inch-plus snowfalls in Philly.

A day such as this on a March 14 is worth savoring, especially if you have any recollection of March 14, 1993.

That day, the region had been layered under an "Arctic landscape," in the words of meteorologist Art Kraus, who worked in the local office.

A foot of frozen snow and ice was cemented in place after the great blizzard of '93. The high that day was 26, the low 19.

But if you're worried about a late-season payback for this May-like intrusion, for now you can stop worrying.