I’ve been meaning to do a wrap-up post for this spring, as it was an odd one: although we had our first April-like temperatures way back on March 4, we’ve been in a kind of limbo ever since, with those same April conditions persisting well into May. Last week we finally got some warm temperatures, but this morning it dipped to freezing and snowed.
I’d like to show you the final graphs for the year.
First the simple Brick Graph.
The 2021 brick gets added to the April 21-25 stack.
You can click on these graphs to see them full-screen size.
Then the slightly more informative Pancake Graph.
This shows how agonizingly gradual this year’s thaw was compared to other years. It appears to be the slowest in my records by a wide margin.
This is partly a matter of definition, because this graph starts the clock when the mean daily temperature goes above freezing on a lasting basis. That began on March 4, but temperatures averaged out to just barely above freezing for weeks.
In a year with strong currents in the lake, ice might have continued to erode steadily despite wishy-washy temperatures, but lake levels were on the low side, and the Lake of the Woods Control Board restricted flow through the Norman Dam to keep them from dropping further. That meant less current, so the channels and narrows that usually open up early kept their ice for quite a long time.
Sean Cockrem sent me an enhanced version of his Cumulative Temperature Graph, which I cheerfully refer to as the Shark Fin Graph.
Sean has enlarged this graph so that you can see more detail. It’s well worth clicking on it to zoom in.
To recap: long winters are wide. Cold winters are deep. Sean uses that to determine whether the ice is likely to be thick or thin, and then estimates how much heat will be needed to melt it all. He assigns a point value to that, and uses the weather forecast to try and guess when that score might be reached.
The first thing I notice when I compare the two winters on this section is that last winter was both shorter and milder than the one before. An interesting detail is the difference in the tiny sections between the blue X and the red dot. This represents the entire thaw from inflection point to ice-free. In the spring of 2020, we had a short steep path from one to the other. Once it (belatedly) started to warm up, it got rapidly warmer, and the lake ice was gone in about three weeks. This year was very different. From that early start on March 4th, the line staggers along—dipping below freezing at first—for over seven weeks before all the ice is finally gone.
That’s it for this year. Here’s hoping the weather picks up and the pandemic dies down.