Minnesota ICE-OUT update

/ Paul Pukite (@whut)

This is an update to analyzing the dates of Minnesota lakes ice-out events, as described on this blog years ago: Ice Out

The trend has been that dates have been creeping earlier, corresponding to warmer winters.

Scatter plot showing the relationship between the year and the number of ice-out days in Minnesota at latitude 43 N, with a fitted trend line indicating a slight decreasing slope.
Scatter plot showing ice-out days in Minnesota at latitude 44 N over the years from 1840 to 2040, with a trend line indicating a slight decline.
Scatter plot showing the trend of ice out days per year in Minnesota (Latitude: 45 N) from 1860 to 2020. The fitted line indicates a slight downward trend, with the y-axis representing ice out days and the x-axis representing years.
Scatter plot showing ice out days per year from 1880 to 2023 in Minnesota, with a fitted regression line indicating a slight downward trend.
Scatter plot showing the trend of ice out day data over the years in Minnesota at latitude 47 N, with a fitted slope indicating a decrease in days per year, represented by red circles and a blue trend line.
Scatter plot showing the relationship between year and ice-out day for Minnesota at latitude 48 N, with fitted regression line indicating a negative slope.

This is all automated, pulled from JSON data residing on a Minnesota DNR server. I hadn’t looked at it for a while, as the original client query assumed that the JSON was in strict order, but the response changed to random and only recently have I updated. The same approach used is to access lake data from common latitudes and do a least-squares regression on each set. The software is described here and available here, based on a larger AI project described here.

User interface displaying a form for plotting data from 1843 to 2025 with a specified latitude of 44.0, accompanied by options to clear data and submit the request.

There are seven anomalous data points1 that point to ice-out dates prior to January, which may in fact be faulty data, but are kept in place because they won’t change the slopes too much

Summary

2013 slopes2026 slopes
43 N-0.066-0.1042
44 N-0.047-0.08595
45 N-0.068-0.10873
46 N-0.0377-0.0416
47 N-0.0943-0.04138
48 N-0.1995-0.0835

The overall average is around -0.08 days earlier per year which amounts to 8 days earlier ice-out over 100 years.

The last “year without a winter” in Minnesota was 1877-1878 which corresponded to a huge global El Nino. One can perhaps see this in the 44 N and 45 N plots showing early outliers but the data was sparse back then. More obvious is the short winter of 2023-2024, where many lakes never froze or one close to my place was really only solid for a time in December. Can look up news stories on this such as the following 

2024: The Brainerd Jaycees Ice Fishing Extravaganza on Gull Lake—one of the world's largest—was canceled for the first time in its 34-year history because the ice was too thin to support the event.

Footnotes

  1. The following lakes showed anomalous ice-out dates, assumed to be late in the previous year or late in the current year, the latter which would be physically impossible
    Lake Cotton @ 46.88259 N (11/23/2010 [day -39.0]))
    Lake Leek (Trowbridge) @ 46.68309 N (12/07/2021 [day -25.0]))
    Lake Little Wabana @ 47.40002 N (12/08/2021 [day -24.0]))
    Lake Star @ 45.06337 N (11/20/2022 [day -42.0]))
    Lake Lewis @ 45.7479 N (11/28/2022 [day -34.0]))
    Lake Unnamed @ 44.81299 N (11/25/2023 [day -37.0]))
    Lake Unnamed @ 44.81299 N (11/26/2024 [day -36.0])) ↩︎

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