For 12 consecutive days, the government’s Storm Prediction Center has logged reports of at least eight tornadoes daily, a destructive and impressive streak that constitutes a record — for now.

“The fact that it’s been persistent is unusual,” said Bill Bunting, chief of the forecast operations branch at the storm center, in Norman, Okla., "but not unprecedented.

“What’s unique about this year is that we have had day after day of severe storms in the same areas.”

Yes, that includes parts of the Philadelphia region. “And you’re going to have another one” Wednesday.

He said a stubborn pattern in the upper atmosphere has been particularly conducive to setting off the severe storms that spawn tornadoes. On Monday, 77 were reported.

A tornado touched down Tuesday evening near the Chester-Berks Counties border, bringing to 17 the number of confirmed twisters in Pennsylvania this year; the annual average is eight.

As for the U.S. 12-day record, Bunting cautioned that the data are preliminary and that it would take a few months to verify the sightings. He said some of the reports might be multiple sightings of the same tornado.

In addition, it is difficult to compare the volume of tornado reports today with those of the past. He said the closest comparable period would have been an 11-day streak of 10 or more tornadoes in 1980.

The tornado streak of all streaks — 70 consecutive days of at least one tornado touching down somewhere in the country — ended on July 1, 1991.

Tornado numbers generally have increased, said Bunting, but the levels of radar sophistication, human development, social media, and pervasiveness of image-recording equipment continue to undergo quantum changes.

As for the hand of worldwide warming, tornado specialists point out that tornadoes are idiosyncratic storms that get their ferocious spin from a complicated matrix of conditions.

“It’s not a cop-out,” said Bunting. “We just don’t know.”