April 5, 2021: Seems slow

I’ve been talking a lot about how favourable our conditions are this year. We had a mild winter that formed less ice than usual. We had an early start to the thaw, and we’ve had mostly higher than normal temperatures. Conditions seemed primed for a record-breaking early ice-out, but that’s not developing.

I’m not saying this year’s thaw is getting delayed, but I am pointing out that it’s gradual.  Gentle reminder that neither Sean or I predicted records would fall.

We’ve had years in the past, notably 2010 and 2012, where the thaw started almost as early as this year, and the ice was gone pretty quick. But I think we’ve begun to lag behind the progress of those years.

I’ll pop the pancake graph in here so you can see what I’m talking about.

You can click on it to see an enlarged, easier to read version.

Remember, each year since 2003 (at the bottom) gets a bar that starts on the inflection date* and ends when the lake is 100% ice-free. The first thing you might notice is that 2021’s line begins earlier than any other. And yet, it looks set to be one of the longest, representing a surprisingly drawn-out thaw for a warm spring following a mild winter.

*Inflection point or inflection date means the date when the air temperature started to average out at above freezing. More precisely, when the Mean Daily Temperature rose above zero Celsius on a lasting basis.

The two years that come closest to our starting point are 2010, at March 8, and 2012, at March 10. Both of those years had reasonably quick thaws, at less than 5½ weeks. [38 & 37 days, respectively, but who’s counting?] To match that, we’d want to be looking at a total thaw by April 10. So that’s where I began the pale blue of uncertainty on this year’s bar. But Sean Cockrem’s prediction, based on presumed ice thickness and air temperatures forecast, is April 20. Side note: this is his stated and preferred estimate, but his simplest formula, without intuitive insights, produced a date of April 25, so I ran the uncertainty zone out that far.

There are two things going on here. First, the earlier you start, the longer it can take, simply because March is apt to be cooler than April, even if temperatures are running above average. Second, air temperature is not the whole story when it comes to getting rid of lake ice. Sean’s model uses data from past years, and that data is all over the map. In other words, every thaw is different, which is why Sean has to make some educated guesses as to what kind of year we’re having.

Last year we got schooled. After air temperatures stayed depressingly low, the ice went in a hurry  (17 days!) There are many factors other than air temperature: snow cover, rain, wind, sunshine and so on. But I increasingly suspect that the biggest one is current.

Most years that I can recall, the water seemed to open up through the Keewatin Channel faster than this year. Sometimes the water spreads from Channel Island to Safety Bay quite quickly. This year it seems to be rather lethargic.

So I happened to be talking  with some friends on Zoom, and one who lives on Golf Course Bay remarked that this winter, the end of their dock iced in for the first time ever. Usually, the current swirling past the tip of their dock prevents ice from forming there, and the ice is notoriously thin in the whole area around the Coast Guard docks. This sparked a conversation about how—although the lake ice was generally thin—the low current allowed people to route some ice roads through usually untenable areas.

To talk about current, we need to check in with the Lake of the Woods Control Board, who strive to keep lake levels safe by altering the outflow through the Norman Dam. Spring is the season when that typically gets trickiest. It’s prudent to keep the lake levels on the low side in March, to allow for spring run-off and flooding. They call this the winter drawdown, and it’s part of their regular strategy. It’s usually followed by the spring refill. This year there wasn’t  much spring run-off, so lake levels have not risen as rapidly as some other years. So the outflow is being kept low, to give the lake levels a chance to rebound.

Here’s the latest bulletin from the Board.

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 changed little over the past week and is expected to remain stable or slightly increase (less than 2 cm or 1 in) over the next week.

Lake of the Woods authorized outflow is 150 m³/s with no changes scheduled.

This time last year, when we had that very rapid thaw, the outflow was nearly four times as high. The current was probably eating away at the ice from below long before the air temperature rose above freezing.

From the air, this shows as open water in the narrows and channels, and ever since I started Ice Patrol, I’ve been paying close attention to those areas. It makes perfect sense that progress of that type is slow this year, despite the mild weather.

So while current is a big factor, its role this year will be passive. Which is one less wild card for Sean’s predictive model.

7 thoughts on “April 5, 2021: Seems slow

  1. Hello,

    One of the largest contribution to ice melt is water vapour condensing on the ice. Each gram of water that condenses releases 580 calories (latent heat).

    Early on in the melt the sun mostly heats the shore lines. The melted water’s albedo is much lower than the white ice. Short wave radiation from the sun mostly bounces off white surfaces. The albedo (percent of short wave radiation reflected back to space) of white ice is quite high (over 90%). As the ice deteriorates and changes colour the sun’s radiation becomes more and more important to the ice melt as the albedo decreases.

    Early on high humidities with nighttime clouds probably contribute the most to the rate of melt. Night time clouds prevent cooling (long wave radiation). Usually cloudy skies also means higher humidities and milder temperatures. Early on cloudy skies (especially lower cloud) would probably be an important variable in your ice melt model.

    Food for thought.

    Louis Legal Retired meteorologist Shoal Lake

    On Mon., Apr. 5, 2021, 07:24 Lake of the Woods Ice Patrol, wrote:

    > icecaptain posted: “I’ve been talking a lot about how favourable our > conditions are this year. We had a mild winter that formed less ice than > usual. We had an early start to the thaw, and we’ve had mostly higher than > normal temperatures. Conditions seemed primed for a record” >

  2. As we all know, there has been a lack of current this year, which has resulted in ice in places with normally no ice. And, as pointed out previously, routes that should be open by now (eg. Keewatin to Keewatin Channel) are not open. As a result, people are seeing the melt as slow. One needs to remember that fairly strong ice formed in these normally current prone areas, and it is taking time to melt this ice. Thus it may well be that it only seems that the melt is occurring slowly, because we are all used to seeing these routes ice free early and judge the speed of the melt by how quickly these routes become ice free.

    I did an analysis a few years ago regarding current. It would seem likely that years where the current was strong would result in early breakup. No such correlation exists, years with strong current do not open up earlier than low current years, other factors seem more important.

    It is my opinion that the melt is in fact occurring quickly in the main areas of the lake. It may well be this year that the usually early open areas do not open much before the whole lake opens. But the Keewatin to Keewatin Channel area is starting to darken significantly and may open soon. I still think that the earlier estimate I postulated of April 14 to April 20 based on when the snow cleared the ice remains valid.

    • Thanks for letting us know that you found no year-after-year correlation between current and melt. I might have looked into it. Snow cover is definitely a big one. I’m toying with the idea of setting up a sort of form to enter + & – values for all the factors, like some role-playing games have for characters.

      • Just a brief historical note. I’ve been reading Miner & News archives as a bit of a CoVID stay-at-home project and in 1918, another early ice out year, the newspaper had a brief mention that in 1878 the steamer Lady O’ The Lake had made its first trip in early April to the Northwest Angle HBC post from Fort Frances with much needed spring supplies destined for CPR survey/work crews working ahead of the rail head.

  3. Sounds like a statistical regression analysis.

    My earlier analysis only looked at whether current affected actual open water date. It did not try to look at whether it shortened the length of time between inflection date and open (I-O). So today I took a look at the two recent years with early inflection dates. In 2012, it was 36 days I-O. The current was very slow that year. In 2017, it was high current, and the I-O was 33 days. So current has a modest effect on inflection date to open. And, last year when I-O was 17 days, outflows at the dam were declining rapidly, so the current was down to what one would call slow by open. Have to conclude that current takes a back seat to other factors by a mile.

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