It’s a question keeping geese, trumpeter swans and dock-owning Minnesotans up at night: when will the lakes open up?
Luckily, John Downing is here to help. Downing is a professor of biology and with the Large Lakes Observatory, also serving as the director of Minnesota Sea Grant. His passion — verging on obsession — is determining when ice-out will happen each year.
With climate change, ice-out has become less predictable, Downing said. Using a combination of factors including snow depth, ice thickness and cumulative heat, Downing developed a series of equations to predict when ice will finally melt. The speed of melting can also depend on the size of the lake and the amount of water flowing into or out of it.
Practical applications
In addition to satisfying curiosity, there are many practical reasons why an ice-out date matters. It's an important date for resort owners, law enforcement can predict an increase in traffic when the lakes are open, and people need to get their cars off the lake well before then.
“What a lot of people don’t realize about (having a vehicle on a lake) is you’re floating your pickup truck on the lake, and you’re using the ice as a boat. It’s not like it’s so strong it can hold your pickup up. It’s a float,” Downing said.
One of the strongest influences on ice-out is cumulative heat, Downing said. If one adds up the thawing degree days over the season, the lake is likely to be open once about 220 is reached. Downing built a widget for this purpose.
To learn more about the science behind his predictions, read his column on the Minnesota Sea Grant website.
Want to do this yourself? Here's how:
- For each day with a temperature exceeding 32 degrees, calculate the average temperature for the day. Add the high and low temperature together, then divide by two. (For instance, the Saturday highlighted above would have an average temp of 27 degrees. First, 37 + 17 = 54. Then, 54 / 2 = 27.)
- To calculate the degrees warming, subtract 32 from that number. Skip this step if you are using degrees Celsius. (Saturday's degrees warming would be minus 5: 27 - 32 = -5).
- If your result is a negative number, change it to 0. (This applies to our example Saturday: we change minus 5 to zero.)
- To calculate warming degree days over the season, add each day's result to a running total. (For example, let's use the eight days in the forecast above: 2.5 + 0 + 0 + 0 + 3 + 10.5 + 11.5 + 7 = 34.5 warming degree days.)
- Once the season's warming degree days reaches 220, your local lake should be clear of ice.
- Let us know how this worked for you! Email comments@kaxe.org.
