May 17, 2022: Aftercasting

We’re not forecasting any more, but Sean always finalizes his graphs to see how close the predictions came.

Short version: the thaw went better than expected.

Before we examine the final version, let’s go back and look at this spring’s first forecast, from late April.

You can click on these to see larger, sharper versions.

Early in the spring, Sean estimated that we’d need to reach a target thaw index of 190 points. That’s the horizontal yellow line. That value of 190 was based on the severity of the winter. Last winter’s freezing index was close to 1900 points, and a ratio of ten to one is his starting point for predicting the thaw.

April Thaw Forecast Graph.

The blue line is formed by plotting this year’s daily temperatures (Mean Daily Temperatures, to be specific). In the early spring, he sketches in the blue line using the weather forecasts, and then as time passes, he replaces the forecast line with actual data.

Now here’s the post-season analysis version.

Final Thaw Graph.

As you can see, the blue line plotted from actual weather reports rose more steeply than the early version based on weather forecasts.

Also, the ice melted at a slightly better rate than the base ratio of ten to one predicted, so the thaw was complete (marked with a yellow star) at a lower thaw index than the target of 190. It happens. Temperature is a big factor in the thaw, but it’s not the only one. Some of the other factors aren’t included in weather forecasts, especially long-term ones.

Perhaps you’d like to see how this spring’s temperature profile compares to other years in our records. Sean has a graph for that, too.

Spring Temperature Trend After Inflection.

In this graph, the timeline across the bottom is synchronized to each year’s Inflection Date, not the calendar date. Also, the lines for previous years continue to plot the rising cumulative index even after the ice is gone. We’re just comparing spring temperature trends, not trying to factor in ice thickness or anything like that.

This year’s data is shown in a dotted line, and it’s the second highest track on the graph. On both this graph and the previous one, that red line that we didn’t quite equal represents 2007, a very warm spring, so we did quite well this year. As Sean commented, once we finally got Mean Daily Temperatures above freezing*, they were often in double digits.

*When the Mean Daily Temperature goes above freezing and stays there, we call that the Inflection Date, and that’s what Sean bases his graphs on.

Lastly, the Shark-fin graph.

There’s really only one change to this. This year’s ice-out date of May 16 has been marked with a red dot, bringing the thaw phase to a close.

Shark-fin Graph.

Sean will continue to plot the summer numbers on here so that we can see how much summer heat we accumulate, which will affect water temperature and the inevitable freeze next winter.

In the meantime, here’s hoping that he can plot a summer fin that is tall and wide, because that would be the sign of a season that is both warm and long.

Signs of spring: The trees are leafing out, and I saw daffodils blooming in someone’s garden today!

Fun tidbit: Sean did some internet sleuthing, and as far as he can tell, Lake of the Woods Ice Patrol is the only website of its kind anywhere in the world.

I think that’s about if for this year. I’d like to thank everyone that helped.

Sean, of course, for the graphs and predictions.

The pilots and drone operators, and everyone who sent in photos. They made Ice Patrol possible this year.

The donors, who alleviated the stress of trying to do this on a shoestring budget. Having enough money to book flights meant I didn’t have to worry about going without aerial photos in the critical weeks.

The people who participated via email or the comments form. I received a lot of very helpful information from those sources, and it’s growing as a way to pool our knowledge.

And lastly, the followers and visitors. Ice Patrol had a busy spring this year, racking up nearly 75,000 views in under five months. Traffic peaked at over 2400 views a day. That keeps me going, and I’m tickled that people check in from all over the world.

Thank you all.

Ice Patrol will now go (mostly) dormant until next spring.

Talk to you then!


May 13, 2022: Forecast Friday

Soon, the ice-out date will be history, and not a matter for forecasts.

But while we still have a little ice left, here’s Sean’s last take on it for this year.

Remember, you can click on this graph to see it large and sharp.

Lake of the Woods Thaw Forecast.

This year’s temperature profile (the blue line) runs parallel to the best case example from 2007 (the red line). Since last week, Sean has updated the path of the blue line to replace forecast temperatures with actual ones up to the present.

His conclusion? Based on temperatures, the lake should be entirely ice-free in the evening of May 17th.

Temperatures are not the only factor in play, though, so there’s still some wiggle room for wind and high humidity to get rid of the ice even faster. Certainly it is very windy today. I think it’s possible that the ice might be gone a day or so earlier than the temperatures suggest.

In the meantime, although there is still ice present, many people will be able to reach their cottages by boat already. For those who cannot, yet, it is only a matter of days.

Satellite imagery is a bit of a tease lately, because of cloud. Yesterday, Terra satellite was able to see only the south west corner of the lake. Today, Aqua got a look at only the east side. In both cases, there was no significant ice visible, but we’re reaching the stage where it would be hard to spot from space.

Lake levels continue to rise. Water is flowing into Lake of the Woods faster than it can be let out. Sean calculates that the surplus amounts to an olympic-sized swimming pool’s worth of water every second and a half. That would raise the lake by an inch and a quarter every day. If that continued for a week, it would come to another fifteen inches, but nobody knows exactly how long the inflow will remain so high.

As mentioned on Ice Patrol yesterday, the water level of the Winnipeg River is so high that it’s raising the water level in and around the Black Sturgeon Lakes. That’s washed out a number of roads, and resulted in an evacuation order for a lot of people that live north of the Kenora Bypass. The evacuees will have a narrow window to get out. The City of Kenora Works Department is attempting to re-open one route with heavy equipment, and they think they can keep that road passable for four hours this afternoon. After that, the floodwaters will close off all the ways out.

You can read more–and see a map of the affected area–at Kenora Online.




May 6, 2022: Forecast Friday

First off, I made mistakes with the previous post. Dated May 5, I forgot to hit the PUBLISH button until this morning. Secondly, the version that went out by email was incomplete. A drone panorama from Paul Leischow was omitted from the version I hastily put out, and the email version will not be updated to show the corrected version.

To see the full May 5 post, click here or visit the Ice Patrol home page and scroll down.

Now, on to the latest. Sean has been tracking how the weather we’re actually getting compares to the weather forecasts he bases his predictions on. You may recall that we put more trust in the seven day weather forecast than the fourteen day outlook.

This time around, that has worked out well. In the week since Sean released his first prediction, the weather was very close to what was forecast. The second week of that fourteen day outlook is now our coming week, and the new seven day forecast for it is more optimistic.

To be clear, the weather forecasts are updated all the time, and new seven and fourteen day forecasts come out every day. But because Sean does his graph on one particular day, the forecast line on the graph reflects the forecast available at that time.

Sean has revised his graph with the new information, and with more confidence.

Remember, you can click on this graph to see a larger version. You should zoom in on that to see it at it’s largest and sharpest.

If you want to refresh your memory, you can see the previous version by clicking here.

So, what’s different? The blue line is steeper. That’s good. It means that the weather forecast is better, and that means we’re likely to hit the target thaw index sooner. Sean is now saying it looks like the ice will be gone a day or two before the May long weekend, instead of just as it begins.

Graph Explanation:

The horizontal yellow line represents the thaw index we think we’ll need to reach to melt all the ice on the lake.

The blue line represents our thaw index this year, based on known temperatures so far, and forecast temperatures for the future.

The red line shows how fast the cumulative temperatures can rise in a very good year. It’s based on the fastest-warming spring in our records.

The green line represents a worst-case scenario based on the weakest, coolest spring we know of.

It’s worth noting that the revised graph now shows that our weather is tracking very close to the best-case scenario, roughly paralleling it. That would give us a thaw that’s very fast. That’s about right for one that happens this late in the year.

Now the fine print.

This graph and prediction is based solely on air temperatures and an assumed thickness of ice based on the winter’s severity. It does not take into account such factors as the strength of water currents, precipitation, humidity, the UV index, tornadoes, tsunamis, or comet impacts.

This graph may pose a choking hazard to pets and small children, especially on a smartphone. Wear sunblock if reading the graph outdoors. Do not attempt to use this graph while driving or operating heavy equipment. Follow regional and local safety regulations regarding eye protection and personal safety equipment. Always unplug the graph before putting your hands near the moving parts.




April 29, 2022: Sean’s Graphs

I know people have been waiting for Sean Cockrem’s graphs. Now that we’ve finally seen temperatures shift to mostly above freezing, he was able to set yesterday as Inflection Date, and start work on predicting how long the thaw might take.

Sean writes:

At long last Iast, I’m ready to declare [April 27th] as the 2022 inflection date. Usually I wait a few days after to make sure that the measured daily means are above zero, but based on how far into April we are and with the 14 day having consistent warm temperatures, I’m going to make the executive decision for this declaration.

This was the third coldest winter so far this millenium. Only the 2013/14 and 2008/09 winters were colder. This was also the latest inflection date we have had in the last 20 years of data collection.

For the forecast, I have set our target thawing index at 190 which is based on an average 1:10 thawing index:freezing index. I’ve entered the forecast data for the next month or so. Keep in mind everything after a week is a guess, and everything after two weeks is based on seasonal temperatures. This year has been anything but seasonal. Having said all that, there is a glimmer of hope that we will be ‘Ice Out’ right around May 20th, which is the Friday of the long weekend. If the temperatures stay below seasonal, it’s going to be a long shot for complete ice out, which is not to say that a good portion of the lake will be open by then.

As far as the season goes, this one will be down to the wire for the next 3 weeks closing in on the long weekend. A bit more interesting on our end than other winters where the ice is off in late April. Fingers crossed we get some sunny warm days.


I recommend clicking on these graphs to see a larger version. Then you should click on that to see the graph enlarged to it’s full resolution.

Let’s start with the updated shark-fin graph.

The Shark-fin graph plots the severity of each winter and marks the beginning and end of each thaw.

The key points to keep in mind:

The downward spikes plot the temperature trend of the winter. A long winter makes a wider spike, and a severe winter makes a deeper spike.

The thaw commences when the Mean Daily Temperature rises above freezing (on a lasting basis) and that date is marked with a blue X. This is the Inflection Date.

The thaw ends when the lake is entirely ice free. That date–when we reach it–is marked with a red dot.

What can we tell about the winter we just had? It was the second coldest on the graph, and as Sean said, this is the latest Inflection Date we’ve seen since we started keeping records. (2003 was the year I started taking pictures, so Sean hunted down the weather data back to that year. Before that, we don’t know when the ice was gone.)

Summary: It was a long cold winter, so we assume thick ice. It was a late start to the thaw, so that puts us behind.

On to the next graph.

The Cumulative Freezing Index compares the temperature path of each winter.

This graph takes some of the same data, but focuses strictly on the winter. Each winter’s Cumulative Freezing Index is shown as a separate line that ends on the Inflection Date, and this past winter is represented by the heavy dashed line.

Key points:

The years are synchronized to the calendar on this graph, so some years have already become colder than others at the starting line of December 1st.

We had a mild fall, so we got off to a good start.

This years line drops lower than most, because we had a lot of cold weather.

It extends further to the right than any other line because it took so long to get to Inflection.

Now comes the speculative graph: the Forecast.

This one takes some explaining. In the first two graphs, we gave the winter a “score”.

The Cumulative Freezing Index is a single number that sums up how much cold weather we had over the course of the winter. This winter’s number was -1887.* That’s nasty.

*Refresher: Sean derives this number by using a simple technique. Once the Mean Daily Temperature drops below freezing in the autumn, he takes note of it every day. If the MDT is -3°C one day, the line drops three points. If the MDT is -5°C the next day, the line drops a further five points.

Sean tracks the rising temperatures after Inflection Day, too. Then, using my dates for ice-out, he looked for a relationship between the freezing index and the thawing index. This got him a rule of thumb: for every ten points on the freezing index, you need one point on the thawing index to get rid of the ice.* That’s a starting point.

There are other factors that can hasten or delay the thaw. Sunshine is always helpful. Rain and wind can speed the thaw along, especially if the timing is right.  Strong currents are a plus. On the negative side, snow is the worst, but clear nights and cloudy days don’t help either. This forecast doesn’t try to predict any of those things. They’ll be wild cards that may mess with this simple prediction, or they might balance out.

*does that seem strangely unbalanced to you? For the purposes of Ice Patrol, there are only two seasons: the one where it’s below freezing, and the one where it’s above. Generally speaking, we have more summer than winter here: the summer spikes on the shark-fin graph are bigger than the winter ones. But the thaw is just a few weeks out of the year. If the thawing index had to equal the freezing index to melt the ice, it would take nearly all summer to thaw the lake. Also, the lake is not frozen to the bottom, because water is weird stuff, but that’s a whole other story.

In any case, this forecast is an estimate. Sean figures that we’ll need to accumulate roughly 190 points to get rid of the amount of ice this winter should have created.

So he goes to the weather forecast to see how long that might take, and you know how those are. As Sean suggested above, the seven day forecast is broadly reliable. (When it’s off, it’s usually in the timing.) After that, the fourteen day forecast is more of an educated guess, and the really long-term stuff basically just goes, “I don’t know… normal, I guess?”

The forecast graph tracks how long it might take for the weather to melt the ice.

So here’s how it looks for now. The horizontal yellow line is set at 190 points. That’s our target. The vertical grey line is the start of the May Long Weekend. That’s not a deadline, it’s more of a  wish. The smooth blue line is the weather forecast. It hits the target on Friday of the May Long.

There are two other lines. The red one shows how the Thawing Index racked up in the best year, and the green one represents the worst spring we know of.

The red line is the easier one to understand. 2007 was a lovely spring. If we could have those sorts of temperatures this year, the thaw would go a little faster. But as far as our records go, that’s a best-case scenario, and a long shot.

The green line is confusing. 2004 was a dreadful spring, and in fact the whole summer was exceptionally cool. The temperature trend that spring was feeble. So how did the thaw go? Not bad. It had been a middling kind of winter (~1500 points), so the target that year was lower. Despite the chilly spring, the lake was clear of ice by mid-May, significantly better than the ten-to-one rule of thumb would have predicted. In terms of modelling, 2004’s data made it an outlier.

In conclusion: Lake of the Woods is on track to be clear of ice right around the long weekend. If the weather forecast is right, and if the rule of thumb holds true this year.

Thanks, Sean!

Keep in mind that we should see steady progress between now and then. Marinas will open. Many islands will be accessible a week or more before the lake is entirely ice-free. That may also be true of Falcon Lake and West Hawk.

Shoal Lake plays by it’s own rules, and often lags a few days behind Lake of the Woods.

Further north, the long weekend and the opening of fishing season may face problems.

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.