It was a cool, crisp morning with low humidity that hinted at fall on the third full day of summer in Washington and across the Mid-Atlantic.

Only 125 miles west of the nation’s capital, it felt like winter.

An instrument station on the floor of Canaan Valley in West Virginia registered a morning low of 31 degrees. By comparison, it was 57 at Washington’s Reagan National Airport and 49 at Dulles International, the coolest temperature readings at those sites on June 23 since 1992.

Canaan Valley’s chilly number was no fluke or misregister. The same site, operated and maintained by Virginia Tech, recorded freezing lows twice last week during a similar sweep of Canadian air across the eastern United States to disrupt summer’s stickiness. And 16 consecutive mornings in May.

Wednesday’s morning low at Canaan Valley was only one degree above the National Weather Service’s coldest temperature in the 48 contiguous states: 30 degrees at Mount Washington, N.H.

Challenging or even beating the officially recognized national low temperature is nothing new for Canaan Valley.

On the morning of May 14, the Canaan Valley station recorded a low of 18 degrees — colder than the 20 degrees at Dixie, Idaho, reported as the coldest temperature in the contiguous 48 states.

“From our observations over the past couple of years, this northern Canaan Valley site has recorded temperatures that are lower than the official reported low in the Lower 48 several times each year,” said Dave Carroll, an instructor in meteorology at Virginia Tech who established and maintains the station and several similar ones in the Appalachians of Virginia and West Virginia.

“I’m working with top-level management in the National Weather Service to get those stations accepted,” said Robert Leffler, who served more than three decades with the Weather Service before retiring and is an expert on Canaan Valley weather and climate.

Leffler, a Damascus, Md., resident but longtime property owner in the Canaan Valley, describes the valley as “a bathtub.”

“Canaan Valley is a textbook-quality large-scale ‘frost hollow,’” he said.

Cold air drains downward to the valley floor, which is over 3,000 feet and rimmed by ridges topping 4,000 feet, on clear nights with calm wind and low dew points.

The narrow channel of the Blackwater River on the western side of the valley is the only exit for that cold air, so it pools, similar to a river backing up into a pool behind boulders. Furthermore, much of the valley and even the surrounding mountains are meadows, which allows heat to radiate upward and outward into the atmosphere faster than it would in forest or, especially, urban settings.

Carroll said the temperature at the floor of the Canaan Valley has sometimes been 30 degrees colder than that at another Virginia Tech instrument site on a ridgeline less than 1,000 feet higher and three miles away.

Temperature sinks like the one in Canaan Valley are found in mountainous areas of the nation both in the East and the West.

“In some ways, Canaan is similar to the famous Peter Sinks site in Utah, a large sinkhole system at over 8,000 feet, which records extremely cold conditions,” Carroll said, referring to a location that often shows up with the nation’s lowest temperature.

Former Weather Service and Weather Channel winter weather expert Tom Niziol, in a blog post, identified Antero Reservoir in Colorado and the Barrens in Pennsylvania as other notable temperature sinks.

The craterlike Burkes Garden in the southwestern corner of Virginia, a valley completely rimmed by mountains, is another.

Leffler said the National Weather Service once had a weather station in the floor of the Canaan Valley that registered low temperatures in the 20s in June, July and August and showed that the valley’s growing season was only 91 days long in the 1961-90 period.

“That’s a week shorter than the average growing season at Fairbanks, Alaska, near the Arctic Circle, in the same period,” Leffler said.

Carroll said Tech’s network of higher-elevation weather sensors in Virginia and West Virginia, including locations such as Grayson Highlands near Virginia’s highest point and Spruce Knob, West Virginia’s tallest mountain, were established in support of research by Lynn Resler, a Tech professor studying vegetation in the highest elevations of the Appalachians.

But they obviously serve a pure meteorological interest, as well.

“The Virginia Tech Geography Department would like to expand the mountain stations to include the Blue Ridge of Virginia and the central mountains of West Virginia in the vicinity of the Cranberry Glades,” Carroll said. “Additional stations along the Blue Ridge would help the NWS monitor cold-air damming conditions that are critical in our winter weather events.”