March 25, 2021: Sean’s first prediction

Sean Cockrem, the guy who contributes the fancy graphs, has come to some preliminary conclusions about when the ice might be gone. Here’s what he said:

Here’s my first crack at a forecast for this year.

A couple notes

• in trying to figure out the required thaw index, I usually take the winter’s freezing index, which in this case was -1250, and divide it by 10 which is the average thaw ratio between the freezing index and the thaw index on the day the ice was out. In this case that would get us to a thaw index of 125.
• when I plotted that line on the thaw forecast window, it pushed the ice out date to around April 25th.
• back to that thaw ratio between the freezing index and the thawing index at ice out. It actually ranges from 4.37 to 17.77 over the last 18 spring thaws with the average being 9.98.  In the 5 winters with lower freezing indexes in the last 18 years, generally the thaw ratio is below 10(which means that it would push out the ice out date even longer…). I have provided a summary of the data in the table below:

So, here is where intuition and gut feeling plays a part in determining what that thaw ratio should be. I have assumed that it will be a bit higher than average and set it at 12.5. That’s not based on much more than the fact that your photos are showing open water, that the ice wasn’t that thick and that the snow cover is probably was thinner than average too. (I could be way off with this)

In the end, my forecast is based on some unknowns including the forecasted weather in the coming weeks as well. And right now with all the unknowns coupled together, it is suggesting that the Ice Out date is around April 20th.

Sean is picking March 4 as our Inflection Point this year, so I guess it’s time to update the “Pancake Graph.”  Inflection Point is when the mean daily temperature rises above 0°C. In other words, when we’re thawing more than we’re freezing. Sometimes I call it Inflection Day or Date.

You can click on this graph to see it full screen.

 

The Pancake Graph

This graph shows the time-span of the thaw in recent years, in order from oldest at the bottom to newest at the top. The blue bar for each year begins on the Inflection Point and ends when the lake is 100% ice free.

I’m not nailing down Sean’s predicted date as if it’s a sure thing. I’m showing a range of between April 10th and 25th for now. Two things jump out at me from graphing this. First, March 4th is the earliest Inflection Point Sean has determined yet. Second, even with the likelihood of an April ice-out, this is not a rapid thaw. In fact, it’s looking like one of the most drawn-out melts on the chart. That’s not crazy. The earlier we start, the longer it takes because of the cool March temperatures. The ice was not thick this year, so that’s part of the reason I allow for the chance of thawing by April 10. That would be extraordinary, but it makes for a time-span more in line with other early thaws.

You might be interested in this article on Kenora Online, about moderate drought conditions in the Lake of the Woods drainage basin.

The article refers to the Lake of the Woods Control Board, so I went to see what their latest news bulletin said. Here’s the part specifically about LotW.

The current level of Lake of the Woods is 322.42 m (1057.8 ft), a 40th percentile level for this time of year. The average lake level decreased by 1 cm over the past week and is expected to change little over the next week.

Lake of the Woods authorized outflow is scheduled to decrease to 175 m³/s on Monday, March 22.

That percentile may change in the next weeks. Usually, spring rains and floodwaters raise the lake levels in the coming weeks. With little run-off expected this year, the present levels are quite likely to look increasing low in comparison to seasonal norms.