Every day for the past 125 years, a member of the Opjorden family has measured the temperature and taken precipitation readings for the National Weather Service.

No other weather observer family in Minnesota has such a long record, and only about eight weather observation sites in the U.S. have been continuously operating for so long, said Michelle Margraf, who leads the National Weather Service’s observing program in the Twin Cities.

“It’s basically the gold standard of a climate record,” she said.

The area around the Opjorden farm in Milan, Minn., hasn’t changed much since O.K. Opjorden began the measurements in 1893. It’s still out in the country, for instance, free from any urban heat island effects.

And the continuous measurements ensure that researchers can make conclusions about how the climate is changing, Margraf said.

“If we have that steady weather station in one location, you can go back and look over time to see how the weather has changed,” she said. “And looking at that record, the state climate office has determined that the temperature over that period of time has risen, on average, about 2 degrees.”

The biggest changes they’ve seen have been in the daily low temperatures in summer and winter. The farm in Milan has also measured an increase in precipitation. The temperature and precipitation trends are expected to continue in a changing climate.

Margraf said weather data from the network of volunteer observers can help officials make decisions about things like transportation and stormwater management.

“It’s just amazing, the dedication that they’ve had,” she said of the Opjordens. “We are so grateful to them for this precious archive of weather data.”