A national tweak of weather reporting reveals new "threads" that upset previously held records.
Great-grandpa always said it was colder in the old days, and now he's got backup.
A national effort to make local weather records more consistent dropped the Twin Cities' all-time low temperature by 7 degrees, from 34 below, in 1936, to 41 below, set in 1888. That's cold enough to freeze mercury.
"As if it weren't bad enough before," said Keith Eggleston, a climatologist at the Northeast Regional Climate Center in Ithaca, N.Y., and coordinator of the ThreadEx data project that the National Oceanic and Atmospheric Administration (NOAA) launched several years ago.
The lower low is a result of the project extending Twin Cities official records 20 years further back, from 1891 to 1871.
ThreadEx isn't so much about bragging rights as it is about making weather records from around the nation more uniform, Eggleston said.
Data from 270 reporting stations around the United States, including the Twin Cities, have been recast to identify single "threads" of weather records, eliminating duplicate or conflicting data from competing weather observers. In Chicago, for example, the new set of weather records replaces as many as five previous versions.
"Everybody was reading off a different piece of music, it seemed," Eggleston said. ThredEx aimed to develop "a database of records everybody was happy with, and to give the public consistent answers."
The Twin Cities area is one of 60 urban locales nationwide for which the official weather record was extended further back into history, beyond the "modern" records that generally began in 1891 with the founding of the National Weather Service. Twin Cities weather records now include data recorded by the U.S. Signal Service from 1871 through 1890.
That means the record now incorporates extremes recorded in the 1880s, "a period of extremely cold winters," said assistant Minnesota state climatologist Pete Boulay. "We were still coming off the Little Ice Age. There were some extremely cold outbreaks. We may never see those again."
That era also was a time when the Twin Cities area had far less of an "urban heat island" than it does now, Boulay noted.
Overall, the project has provided the Twin Cities with 16 new daily record highs and 82 new record lows.
The all-time record Twin Cities high, 108, on July 14, 1936, remains unsurpassed. Ditto for the single-day precipitation record of 9.15 inches, set July 23, 1987.
The data project also pulled in at least once instance of significant warmth from the old days: the "Year Without Winter," the months of December 1877 through February 1878, now officially the warmest winter on record in the Twin Cities. Without that winter on the list, the season just past would have been third-warmest, instead of fourth. Similarly, February 2012 would have been ninth-warmest, but under the new reckoning it's 12th.
"It's harder to make a top 10," Boulay said.
Eggleston said the new data should not serve as evidence of climate change, since they deal with extremes and not long-term trends. The study's point, he added, was to link observations from different sources, and such variations would undermine any climate measure. The weather record for the Twin Cities, for example, now includes observations taken over time in downtown St. Paul, downtown Minneapolis, St. Paul Downtown Airport and Minneapolis-St. Paul International Airport.
So what's the point?
"It gives you an idea what's in Mother Nature's bag of tricks," Boulay said. "It'll probably never get to 40 below again, but it's good to know it did happen."
Bill McAuliffe • 612-673-7646