Lake Pepin: Ice Thin, But Getting Thicker

The first Lake Pepin ice measurements of the season on February 12 in the Upper Mississippi River showed lower ice thickness, following what scientists say has been the warmest January on record. But the ice thickened again as temperatures dropped in February.

The National Ocean and Atmospheric Administration said this January was 2.05 degrees Fahrenheit above the average January temperatures for the 20th century, resulting in thinner Lake Pepin ice.

A comparative chart showing measurements between 2011 and 2020 showed the February 12 ice as the thinnest at this point in the year at River Mile 770, at an average of 10 inches thick. The Lake Pepin ice was 17 inches thick at its thickest point at Mile 770 on February 12, narrowing to a few inches at Point No Point.

However, the February 19 measurements showed a thickening of several inches at the thickest part, to about 18 inches by February 19. The lower end of the lake (which isn’t really a lake but the widest naturally occurring spot in the Upper Mississippi River) showed no ice, but the iced portion was extended downstream by two feet by the February 19 reading.

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The Corps takes ice measurements on Lake Pepin annually to forecast the navigational outlook on the Upper Mississippi River. Lake Pepin is located between the Minnesota cities of Red Wing and Wabasha. Measurements taken here give the best outlook, as it is the last segment in the navigation channel in which winter ice will break up. The information is used by the navigation industry to predict when it’s safe to break through the ice and begin the 2019 navigation season.

Normally, ice measurements are completed weekly, or biweekly, until the navigation season begins. The St. Paul Engineer District takes the measurements using an ice boat and confirming them with GPS readings.

Historically, the average date in which navigation is open occurs during the third week of March. The next ice measurements are scheduled for March 4.

The data will be posted on the St. Paul District’s website.