Re-Writing History? Climatologists Question Lake Minnetonka's 1856 Ice Out Accuracy

The latest “ice out” on Lake Minnetonka was recorded way back in 1856—when it wasn’t until May 8 that observers deemed the majority of Lake Minnetonka navigable.

But that unexpectedly changed this week after the Freshwater Society, the official caller of ice out on Lake Minnetonka since the 1960s, removed the 1856 entry from its historical data.

“The Minnesota Climatology Working Group this month raised questions about that date because of some old temperature records that show a very warm April that year,” Pat Sweeney, the Freshwater Society’s Communications Director, said.

Sweeney went on to say the April of 1856 followed some bitter cold nights earlier in the winter, adding the entry was removed from the record while researchers attempt to answer questions about the spring of 1856.

“We are continuing research to try to pin down when the ice went out in 1856,” he said. “That leaves May 5, 1857, as the latest ice out in the record. April 1857 temps are consistent with a very late ice out, according to the working group.”

Ice out dates for 22 of the years since 1855 are unknown. Several years ago, Pete Boulay of the Minnesota State Climatology Office found old Smithsonian Weather Observer records that contained ice out information for two years—1863 and 1873—that had long been missing from the official log.

Last year's call came at 9:12 a.m. on Wednesday, March 21.

Freshwater Society founder Dick Gray, who catalogued the early records and has made his own records since 1968, described the standard for determining ice out in a 2003 column: “when it is possible to travel by small boat from any one shore to any other shore through any passage on the lake.”

Prior to that, Gray wrote, ice out sometimes was determined by when a car placed on the ice fell through or when a boat could travel from Excelsior to Wayzata.