March 17, 2021: Sean’s Graphs / Minaki

Sean Cockrem has been busy plotting. Data, that is.

Here’s his interpretation of what kind of winter we had, in two graphs.

You can click on them to see them full size, it makes them easier to read.

I’ll start with this one, because I find it easier to explain.

The graph starts on December 1st, and each year gets a different coloured line.

Freezing Index means the daily mean temperature (when it’s below freezing) and cumulative means we adjust the total score with each new day. Celsius makes this easy: mean temperature of -10°C? Drop the line ten points. It’s a simple system for comparing the severity of winters. Which is not to say it isn’t a ton of work. Thanks Sean!

A cold winter has already scored some negative points by the time December rolls around, so the lines have already begun to draw apart at the start. A miserable winter, such as 2014, seen here in grey, drops steeply and gets to a very low cumulative index by the time spring comes around.

The winter just ended is shown as a dashed brown line. It starts out fairly mild, and is actually in the running for the mildest in mid-January, and then we had those bitterly cold weeks in February, and it dropped to third or fourth place. But all in all, it was a gentle winter.

Here’s another way of representing the data: this second graph shows the seasons one after the other, instead of overlaying them on top of each other. For now, lets ignore the upper spikes: those represent the summers. The lower spikes show the last eight or nine winters. A wide spike is a long winter, and a deep spike is a bitter one. Last winter, at the right, was neither.

As of today, the index sits at around 1250. The blue Xs mark the inflection points, the day when the daily mean temperature rose above freezing for keeps. Sean hasn’t put one in for this year yet, because we’re kind of hovering right around freezing. In his email, he explains that he thinks we’ve reached that point, but the numbers have us kind of coasting along, neither warming up for a proper thaw, nor cooling off to refreeze. The weather forecast leans towards warmer, so time will tell.

Okay, now we can talk about the summer side of this graph. After we reach the inflection point, the winter ends with a vertical line, and the graph switches over to plotting the thawing index. You guessed it; if we have a mean daily temperature of 5°C, Sean adds a point to the line that’s five points above yesterday’s.

And that brings us to the purpose of this graph. If we know how long and cold the winter was, Sean can make an educated guess about how much spring warmth we’ll need to melt the ice. The red dots on the graph represent the days when I declared the lake ice-free. But even before that happens, Sean attempts to calculate what thawing index we’ll require to melt everything, and then he goes to the weather forecast to see how long that might take.

Which is where it gets tricky. Because:

1) weather forecasts have been known to be wrong. Shocking, I know.

2) especially long-term forecasts.

3) there’s more to melting ice than just air temperature. Sun and rain and wind all have effects.

4) ice melts from below, too. Current erodes it, and water gets into the cracks.

So, it’s not time to make bold predictions yet. But what we can say is: this was a mild winter, and it shouldn’t take all that long to melt the ice.


Luke Burak took some aerial photographs today of the area north of Minaki.

You can click on the photo for a closer look.

Minaki & Gun Lake


Minaki is dead center in this picture, with Gun Lake behind it, so we’re looking roughly south.

Luke’s other pictures were further north, up around Wabasemoong (Whitedog), Caribou Falls and Umfreville Lake. That’s a little outside my usual coverage area, so I’ll just say there was only a little open water on that part of the Winnipeg river so far.

Thanks Luke!

May 10, 2020: Ice Free

With temperatures below freezing last night and most of this morning, I wasn’t sure if it was safe to say all the ice is gone. The largest patch remaining was on Bigstone Bay, which was going fast on May 8th.  My sources there tell me it vanished yesterday.

So I’m calling Lake of the Woods ice-free as of May 9th this year.

Brick Graph

On the Brick Graph, 2020 falls near the middle of the pack. That’s kind of disappointing for a spring that had relatively thin ice.

You can click on the graphs to see them full-screen.

The “Jenga” or Pancake Graph tracks the thaw from the Inflection Date (when the mean daily temperature rose above freezing on a lasting basis) to the day Lake of the Woods is ice-free. Years are stacked chronologically, with the most recent year at the top. The 2020 final version looks like this:

Pancake Graph

The thaw went fast after the air temperature rose above freezing. It’s probably safe to assume that a lot of the ice was melted from below, by the lake water, before air temperature had a go. This graph doesn’t attempt to factor that in, so it shows this year’s seventeen days as the most rapid thaw in recent years, after getting off to a late start.

The more I learn, the more I realize I don’t know enough. There are so many factors at work: ice thickness, snow cover, air temperature, sunshine, wind, rain, water levels and current. One year, my predicted date will be correct. And you know what? It won’t be from correctly calculating the effect of all those things. It’ll be a fluke.

Speaking of things I’m unqualified to comment on, I had some people ask if I know anything about when the Canada-USA border might open. Well, no, I don’t.

But I can certainly see that it doesn’t make sense let Americans flow freely into the country while we’re still trying to keep Canadians separated from one another to reduce the risk of exposure.

The two countries have chosen very different strategies, and they can’t really be melded. While Canadians are being paid to sit tight, and have the assurance of medical coverage whether they work or not, the US has leaned towards sending people back to work, even going so far as to open places like meat-processing plants despite high rates of infection.

It’s a safe bet that the rate of exposure is much higher in the US than here. It certainly is in places like New York. Until recently, only sick people were getting tested, but we need to know how widespread the infection is in the general populations of both countries.

If the US approaches “herd immunity” numbers while exposure in Canada is still relatively rare, opening the border would cause a huge outbreak here.

So I think it might have to wait a while, and it’s quite likely going to cause problems of one kind or another.



April 27, 2020: Jason Duguay / Sean Cockrem

Here are the latest pictures from Jason Duguay, taken from the ORNGE helicopter yesterday.

You can click on these pictures to see them full-screen and zoomable. That’s worth doing, by the way: you can get a much better idea of the condition of the ice, even in the distance.

Devil’s Gap, with Goat Island and Johnson Island sitting at the edge of the ice.

Rat Portage Bay, with Gun Club Island in the middle.

West end of Coney Island, and the Yacht Club end of Keewatin Channel.

I’ve been asked about predictions. There are two ways we can do this: science, and history.

Let’s start with Sean Cockrem, who does the science.

To recap, Sean gauges how cold the winter was by totalling up the mean daily temperatures for all the days where the mean was below freezing. That gives him an idea of how the ice thickness might compare to recent winters. Based on other winters, he calculates how many warm days we might need to thaw that amount of ice. Then he goes to the long-term weather forecast (which has let us down before) to try and work out an approximate date when we should accumulate enough heat to melt all the ice.

We had a warm spell in late March, and it looked as if the thaw might be under way. Then the first three weeks of April were miserably cold. Not just below average, but mostly below freezing, and sometimes way below. If we melted a little ice in the afternoon, we refroze it overnight. So Sean’s original interpretation that we could say the inflection date–when the mean daily temperature rose to be consistently above freezing–could be pegged at March 26, had to be revised. By nearly a month! We finally turned the corner on April 22nd.

You can click on the graphs to see them larger and full-screen.

Here’s a graph that compares the severity of the last few winters.

Each winter is depicted as a downward spike. The colder the winter, the deeper the spike. And the longer the winter, the wider the spike. Last winter, at the right hand side of the graph, was not terribly cold, but you can see how it dragged on, and right at the tip of the spike is our nasty little cold snap, shaped like a little claw.

Okay, so we know what kind of winter it was. What can that tell us about the thaw?

On this graph, the lines all begin on the inflection date, but the dates shown are for this year. The idea is to show how 2020 compares to the best and worst years if you line them all up at the starting gate.

The blue line is 2020, with dots for each day’s actual mean temperature. Looking ahead, the yellow line shows how it will go if the weather forecast comes true.

Part of this prediction is an educated guess. Because we know late springs tend to melt faster than early ones, Sean chose a thaw index that takes into account longer sunnier days, instead of just blindly applying the same mathematical formula. His tentative conclusion? We still need about three weeks to get the lake entirely ice free, and we should make it just in time for the May long weekend, which is early this year, at mid-month.

Before I had Sean crunching numbers, I made predictions in a rather simpler way: I looked through my archives to find pictures that showed a similar extent of ice, and then I checked to see how long it took to melt that time.

You can do this yourself, if you like. There’s an archive tool on the Ice Patrol website that lets you look through the previous several years month by month. I have pictures from April 25th from both 2018 and 2019, and it looks as if this year is kind of in between, but roughly the same.

Here’s what I call the “Jenga Graph” it shows a stack of sticks, with each one representing a thaw starting on the inflection date and ending on the day the lake was 100% ice free. The most recent years are at the top, and 2020 is pale blue because it’s just a guess.

This graph reveals that we really did get a late start on the thaw this year. Of all the years since 2008, only 2013 had a later inflection date than 2020. That doesn’t have to mean the ice will last longer, though. Although the ice has been reluctant to melt, it was not very thick this year.

So it looks as if Sean and I agree pretty much to the day. That doesn’t mean we’ll be right, of course! We’ve been wrong before. Sigh. Almost always.

Sign of spring: the snow sculptures on the harbourfront have finally melted completely. Ice is out on Kenora Bay.

Just like every year, the lake will melt. Unlike other years, we may not be able to enjoy it much. Until restrictions for the pandemic begin to lift, very few of us will be able to get out there. Even when things start to improve, some form of physical distancing will probably still be necessary. Large gatherings will have to wait. I don’t think we’ll be tying our boats together, or sharing drinks from a common cooler, anytime soon.

Be strong. Be patient. Be healthy.



March 25, 2020: No more flights

I’m sorry to tell you that I will not be flying during this year’s thaw. The company has no clients actively flying or likely to book trips in the next several weeks, so temporary layoff notices have been sent out. I do not expect to fly again until summer. Training flights have been cancelled. We have one crew available in case something comes up.

I could try to do a post once a week or so, with satellite imagery and graphs, but I won’t be able to observe or comment on the stage by stage developments on the lake.

On the bright side, the spring will come whether I document it or not. The Canada geese are back now, and the hardy goldeneye ducks have been around for weeks.

Sean sent me a couple of graphs the other day. Now seems like a good time to put them up.

2020 Year by Year

On this graph, cold temperatures drive the winter spikes downward, so that a long cold winter has a deeper and wider profile than a mild one. Last winter, looking unfinished at the right side of the graph, seems to be one of the milder ones. Sean uses this data to guess at the overall ice thickness. Then, once our temperatures are above freezing, he makes an estimate of how many warm days it will take to melt it all.

For a different way of comparing the winter to previous ones, he produces this graph:2020 Year Comparison

Each winter gets its own coloured line, tracking a simple points system: each day, the mean daily temperature moves the line down that much. If the daily mean temp is -10ºC, the line drops ten points. This year is the fat dashed line, and if temperatures level off the way Sean extrapolated, we can see that recently there have been six longer, colder winters, and just three milder ones.

That’s all for now. Stay well.



May 14, 2019: All Clear

I believe Lake of the Woods is 100% ice-free today. So here’s a look at how the spring went, in graphs. You can click on the graphs to see a full-screen, zoomable version.

First, the Brick Graph. Each year gets a brick, and I stack them according to when the ice went out. For simplicity, I divide April and May into five-day periods.

2019 was not an early thaw. Of the last sixteen years, only 2014 was significantly worse, and that was a dismal spring after a brutal winter.

Here’s a slightly more complex graph, that shows not just the date the lake was clear of ice, but the length of time from when it started melting to when it finished. More specifically, each horizontal bar spans the calendar from the Inflection Date, when the mean daily temperature rose above freezing on a lasting basis, to the Thaw Date, when the lake was entirely free of ice.

2019 is at the top, 2018 just below, and so on, down to 2008, the earliest year Sean worked out an inflection date for.

Some fun trivia from this graph: Our inflection date was April 13th this year. 2016 shared the same inflection date, but the lake cleared by May 4th, a full ten days earlier. The ice was probably a lot thinner that spring, because the winter had been mild. 2010 was an extraordinary year: the lake was completely clear by mid-April!

Here’s a graph from Sean that shows how our spring temperature profile compares to other years.

On this graph, all the springs are lined up with Inflection as Day Zero at the left regardless of the calendar date. Each year gets dots in a different colour, and day by day, the mean temperature is added to the rising total. A spring with a string of hot days will produce a steep rise, a cooler spring will show a flatter line. The solid red line is the average for all the years since 2003. 2019 is the thin blue line, and Sean points out that although we did better than average at first, we fell behind about halfway along and never quite caught up.

Anyway, that’s the kind of spring it was, but the lake’s open now. I won’t be doing regular updates any more until next year. I expect I’ll fire up the Ice Patrol again on the first day of spring, or the inflection date, whichever comes first.

Thanks to everyone who came by to visit the website and shared word of it with friends, and a special thanks to my guest photographers and my co-workers at MAG Canada who made it possible for me to offer updates on days when I didn’t fly.

Talk to you next year,


May 13, 2019: The Last Ice

Today I went looking to see if any ice remains on Lake of the Woods. I did find some, south of the Barrier Islands, but it’s just little patches of loose, candled ice.

The photo above is from around 10:00 this morning, and looks south over Allie Island towards the Alneau Peninsula. I’ve circled the area of interest so you’ll know where to zoom in for a better look. At full resolution, that’s clearly ice.

I thought a little patch of weak ice like that wouldn’t last long, so I was looking forward to checking on it on my return in the afternoon.

We came back at about 5:00 and after checking to see that Big Sand Lake, north of Minaki was open, (too far away to photograph, but it is open) I started with a picture of Shoal Lake.

As far as I can tell, Shoal Lake is wide open. Because it’s deep, It often clears about three days later than Lake of the Woods, but this year it cleared earlier.

Next shot, Big Narrows.

Looking south. Left of centre is Wiley Point, with Big Narrows above the middle of the picture. In the distance, is that ice on Little Traverse? It was so hazy I wasn’t sure, but there was ice there the other day.

Next, I checked on that ice south of Allie Island.

In the centre of the picture, you can see it’s falling apart, but it’s not gone.

There was a lot of discussion about Bigstone Bay over the weekend, so I wanted to get a bird’s eye view.

This picture is centred on Scotty Island, with Middle Island and Hay Island stretching away to the right. Bigstone Bay appears to be entirely clear.

Next, a closer look at Bare Point and Pine Portage Bay.

Bare Point Marina and Northern Harbour, on Pine Portage Bay, are key access points for Bigstone Bay and Hay Island. Both are wide open now. I counted about twenty boats in the water at Northern Harbour this afternoon. There might be more, but the bigger boats are easier to see.

So although a small amount of ice persists, the lake is essentially open for boating.

Let’s go to the satellite imagery, Bob.

Aqua‘s image was spoiled by cloud today, but Terra got a pretty good shot. The white circle encompasses Rabbit Lake, Round Lake and Laurenson’s Lake, which are good markers for picking out Kenora. The small red circle is the surviving ice south of Allie Island. The large red circle indicates the area of possible ice on Little Traverse, but the satellite image shows nothing except a streak of cloud.

Fun with Clouds, Part Two: at the top left, our friends the fair-weather cumulus. At the right, in blue, high altitude clouds made of ice crystals. In the lower part of the picture, clouds of vertical development: towering cumulus or nascent thunderclouds, with watery bases and icy tops. When clouds like this become full-grown thunderheads, the vertical movement of water droplets up and down through the freezing level forms hailstones.

Summary: only one tiny patch of weak ice remains on Lake of the Woods today, and it will be gone tomorrow.

That means we’ll be ice free on exactly the same date as last year, which kind of makes sense given how the winters were similar in both duration and coldness.

I say kind of, because although the winters had a lot in common, the springs were quite different. 2018 was a late, cold spring that turned really warm at the end of April. 2019 was a slow, cool spring with few warm days.

Here’s Sean’s updated graph of our temperature progress this spring.

Overall, you can see we had moderate thawing this year, with the blue dots showing that mean daily temperatures added up slowly, especially in late April. When Sean and I first modelled this year’s forecast, we chose a thaw index of 240, because that’s how much heat it took to melt last  year’s ice, and the two winters were similar. In the end, although the predicted date for ice-out came close, the actual amount of heat it took to do it was less than we thought, and this graph shows a revised forecast with the expected thaw index reduced to 190.

Basically, we assume that a long cold winter makes lots of ice, and it will take lots of warm days to melt it all. That’s simplifying, and we know it. The brutal winter of 2014 thawed with an index of 194, so 190 is not unreasonable. Perhaps last year’s 240 points was an oddity.

In any event, we didn’t need as many thaw days as we first thought. Sean offers these technical insights:

Sources of error are plenty in this high level statistical analysis. Wind, direct sunlight, rain, ice thickness, snow thickness etc are all variables that the analysis does not take into account.

Our ratio of freezing index to thawing index was right around 10 this year, which is the average for the last 15 years or so. Our initial prediction this year was conservative based off of last years data and went with 7.5 freezing index to thawing index ratio.

If we had ignored last year’s unusual thaw, we would have used a ratio of 10 and gone with an index of 200. That would have been close.

That’s basically it for this year. I’ll do a wrap up post when I can confirm that last patch of ice is gone, and I’ll update the different graphs that show how this spring compares to recent years.

Now that boats are hitting the water, it’s time for my annual reminder that the stretch of Safety Bay from Bush Island west to Norman is a licensed Water Aerodrome: an airport for float planes. Please watch out for them when boating in this area. Think of it as a runway. For safety reasons, float planes have the right of way when taking off or landing. When taxiing, they are supposed to be like any other watercraft, but from experience, I can tell you that they cannot decelerate quickly or turn sharply. Do be careful around them.

May 1, 2019: Marinas, Aerials and a Graph

Lots of stuff today. I’ll start with some contributor photos, move on to a handful of fresh aerial photographs, and finish with a look at Sean’s Thaw Graph and the weather outlook.

You can click on any of the images to see them full-screen. Some will be higher resolution than others.

I got photographs from three contributors today that follow up on my marina report from yesterday. Here they are in the order I received them.

Al Smith sent me this picture of the docks at Smith Camps on Thunder Bay.

Smith Camps on Thunder Bay.

This shot looks out from Thunder Bay at Bigstone Bay.

Then Ian Bruce sent me this look at Bigstone from a different vantage point.

Ian says: Taken from mainland on Branch road 6A, looking south to Hay Island. Boulder Island middle distance to the east side touching flag pole. Still lots of ice, shorelines thinning to a bit open.

A little later, Brian Finnegan sent me a picture  of Henderson’s Marina on Route Bay.

Henderson’s Marina, Route Bay.

Looks like things are coming along there.

In a separate email, Brian attached this shot of the docks at Northern Harbour.

Docks at Northern Harbour, Pine Portage Bay.

Brian mentioned that marina operator Gary Hall said he hopes to be putting boats in the water next week.

Thanks to Al, Ian and Brian for taking the time to send me their pictures to share with you.

Okay, on to aerial photographs. Today wasn’t great weather for taking pictures. Luckily, I grabbed a few shots in the morning, just in case the afternoon was poor. This turned out to be the right choice: although we had low cloud in the morning, we had lower cloud in the afternoon, with showers as well.

So, I’ll start with the standard view of downtown Kenora I get after we lift off from Runway 26 and climb to the west.

Laurenson’s Lake is open now, and so is Round Lake (not shown in this pic) Rat Portage Bay still has some ice, but it looks very weak.

As we start to swinging south to head east to Dryden, we get a look at the area south of Devil’s Gap.

In brief: Matheson Bay at the left, Gordon and Galt Islands near the middle, Rogers and Treaty Islands at the right. The ice looks soft here, too. The channel into Devil’s Gap is open at the lower left, partly blurred out by a propeller blade.

Next, as we continue to turn from south to east, we look at Bald Indian Bay.

Sultana Island dominates the middle of the frame, Pine Portage Bay is behind that, and Heenan Point extends almost to the right edge of the picture. Thunder Bay lies behind it.

Okay, remember how I said it was a good thing I snapped a few pictures on the way out this morning? Here’s what it looked like in the afternoon. I had to grab this shot through the side window; it’s impossible to shoot through the windshield with our high-speed wipers going.

Anyway, this looks south west at part of Bigstone Bay with Heenan Point at the right and Hay Island emerging from the rain in the distance.

Now, on to the weather situation.

I had to email Sean to ask him to update the Thaw Graph. As you can imagine, it’s not good news, and he didn’t want to depress everyone. Even so, I think it’s a useful way to picture the temperature trends and their significance.

Click on the graph to more easily read the fine print. The blue line with dots represents how our daily mean temperature is adding up towards our goal. (Set to 240 points based on similar ice-making conditions last winter.) With recent temperatures barely squeaking above freezing, that upward progress has levelled off lately. That means a delay in accumulating enough warm weather to melt the presumed amount of ice.

Which brings us to the forecast. A normal daytime high this time of year is around 15ºC. The current  Weather Network forecast doesn’t call for a temperature that warm until mid-May. Forecasts can be wrong, of course, and they’re most certainly subject to change. But it seems likely that we’ll be spending the next two weeks struggling, (and mostly failing) to reach double-digit highs. At night, we’ll be close to freezing.

If there’s a bright side, it’s a peculiar one: miserable weather can also remove ice. Rain and wind are not as nice as sunshine, but they do transfer energy that can melt and break up ice. As we head into May, I’ll take any help we can get.


April 23, 2019: Graphs

I didn’t fly today, so I’m catching up on some graphs and predictions.

First, an updated graph from Sean C. You can click on it to see it full-screen.

To recap:

The blue line with the plot points tracks our actual daily mean temperatures so far.

The yellow line is based on weather forecasts. In theory, this is the path that the blue line will follow, but it gets less reliable the further into the future you look.

The solid red line represents a warm spring that racked up lots of high daily mean temperatures in a short time. It’s sort of a best-case line.

The solid green line represents a cool spring that took a long time to deliver a decent amount of heat. This is more of a worst-case scenario.

The horizontal dotted red line represents our goal for this year, a thaw index of 240. As each day’s mean temperature gets added to the blue line, we rise towards that goal.

The target index of 240 points is based on last year because the winter conditions were very similar as to both the length of the winter and the depth of the cold.

The vertical dotted red line indicates a date we might make it by. It was set to May 17th when this graph was first created, but we’ve already started to improve on that.

We might have an easier thaw if last winter’s frequent snowfalls degraded the quality of the ice compared to 2018. Soft ice wouldn’t require as many warm days to melt, so we could do it with less than 240 points.

Here’s a graph I made, using data provided by Sean, but presented in a different way. It’s wide, so you should probably click on this one to see it clearly.

I’ve given each year a horizontal bar that starts on the inflection date (when the mean daily temperature rose above freezing on a lasting basis) and ends on the day Lake of the Woods was ice-free. The most recent year is at the top, and the oldest year (2008) is at the bottom. Rather than line up all the inflection dates at the left edge, I displayed them on a calendar base, because a May thaw is apt to apt to get more hot days than a March one. You can see this: the lines that start really early run longer than the ones that start late.

Now it happens that our inflection date this year was April 13th, the same as 2016. I’m confident that this thaw will take at least as long as 2016’s, which ended on May 4th, so this year’s bar is solid blue up to that date. Realistically, there’s little chance of getting off that easy. The winter of 2015/2016 was a mild one, and the ice didn’t put up much of a fight.

I’ve tentatively shown a longer period of uncertainty in pale blue. I ran that out to as late as May 17th. That’s to match the prediction from Sean’s graph. I’m really hoping that’s on the pessimistic side. I didn’t have the heart to project anything worse.

It might be possible to be ice-free around the middle of the range—May 10th or 11th—if we thaw as fast as last year. We’re doing well in that regard right now, but there’s cooler weather forecast for the weekend and next week that could slow things down again.

The final result may depend on two basic things: how much ice we can melt during our current warm spell, and how that forecast cooler weather plays out.

There are also two wild cards: rain and wind. Rain has an enormous capacity to deliver heat energy deep into ice if there are cracks. Wind can do violent damage to ice sheets once there’s open water in contact with them.


April 15, 2019: Sean’s Analysis

I didn’t do a Signs of Spring post yesterday, but if you’re interested, snow is retreating wherever the sun shines, but lingering in shadowy places. I’ve seen a pair of Mallards, my first ducks of the year. Also a pigeon and a pair of Whisky Jacks. I heard a second-hand report (hearsay!) of a robin. Cyclists are emerging from their winter dens.

And now onto the main topic.

Contributor Sean C. is finally confident that we’ve reached the inflection point, the date when our daily mean temperature rises above freezing on a lasting basis. He figures this took place on Saturday, April 13th.

That means that from now on, the ice will be melting steadily.

Here’s the first of his graphs, depicting the severity of the winter.

Each of the downward spikes represents a winter, ending on the date of the inflection point. The depth of the spike represents the severity of the winter, and the width of the spike represents the duration of the ice-making period. In a nutshell, the winter that just ended was not the worst, but it was a very close match for the previous winter, which was pretty bad.

You can click on these graphs to see them full-screen and a bit bigger.

Here’s Sean’s graph comparing the way some recent winters unfolded.

2019 Freezing Index

In this figure, each winter gets a line in a different colour, and tracks across the calendar until it ends on the inflection date. A short shallow line, like 2012’s medium blue one at the top, represents a mild winter that started to thaw early. The awful winter of 2014 (which was also the deepest downward spike on the first graph) is the grey line that slopes down and down, making ice until mid April. Above that are two lines that track together at the end. The dark blue one is from a year ago, and the dark red one is this year. These years look as closely matched on this graph as they do on the first.

Okay. We’ve established that it was a crummy winter that dragged on into the middle of April. Now what?

Well, now Sean uses some math to figure out how much heat we’ll need to melt the ice formed over such a winter. He works out a thaw index based on the severity of the winter. The index lets him make predictions based on the long-term forecast, and it works like this: If a day has a mean temperature of 5ºC, we add five points to the total. If a day has a mean temperature of 7º, we add seven, and so on*. Then he works out how many of those points we’re likely to need to thaw this winter’s ice.

2019 Preliminary Forecast

Sean’s first version of this graph used the same thawing index he forecast last year: 200. However, when I asked Sean if it might be better to use the actual index of 242 that came to pass, he reconsidered, and issued a new version of the graph using an index of 240.

The amended graph now replaces the earlier version on this post. The higher index adds another day to the estimated time until we’re ice-free.

On this graph, the red line represents a really warm spring (2007) that hit 200 points in early May and the green line depicts a cold spring (2004) that took much longer. Please note: this graph isn’t about the thaw in those years, it’s just about how rapidly we accumulated enough warm weather. The very short blue line hiding in the lower left corner is 2019, with data points marked by blue dots to show the actual daily mean temperature achieved. The yellow line is what the weather forecast says we’re likely to get. If the forecast is accurate, the blue line will grow along the yellow path, and Sean will extend the yellow line as new forecasts come into effect. (There are longer forecasts, but plotting them day by day at this point would be wishful thinking)

The horizontal dotted red line indicates the target thaw index of 240 estimated for this year, while the vertical dotted red line marks the date we might reach it, based on the trend in the longer-term forecasts.

*A sort of fun thing we learned about daily mean temperatures: you might suppose that if the daytime high was 10ºC, and the overnight low was 0ºC, then the mean daily temperature would be 5ºC. That turns out to be not quite right. Actually, such a day is likely to produce a mean temperature closer to 6ºC. We seem to spend more hours near the high than the low. Perhaps this is due to spring’s long days and short nights.

If you’ve been following along, you’ll have noticed that the predicted date for reaching the target of 240 points is May 87th. May 18th is bad. It’s even worse than last year, mainly because the temperatures forecast for the next weeks are not high.

Still, there are other factors to consider.

The index itself is not precise; it’s an educated guess based on turning a limited set of  past data into a mathematical formula.

A more positive influence might be ice quality. All that snow this winter made for some poor ice. If it’s weaker and softer, it should melt faster.

Then there are the usual wild cards: rain, wind and sunshine.

In summary, this year looks a lot like last year. Rosy forecasts haven’t panned out, and a normal ice-free date in early May looks unlikely.

Plan on the middle of May and cross your fingers.



March 19, 2019: Graphs

Yesterday I talked briefly about Sean’s method for analyzing the winter temperatures to see how much ice we were likely to have. Here’s his first graph for 2019, an update that shows how this winter compares to the last few.

Each spike above the center represents a summer, with the rising line showing the degree days above freezing. When the mean daily temperature falls below zero in the autumn, the line drops vertically and the downward spikes show the degree days below freezing.

A spring day with a mean temperature of 10ºC would be ten degree days.

Based on the severity of the winter Sean estimates how many degree days it will take to thaw the lake, and then looks at the forecast to see how long that might take.

It doesn’t matter much whether we have eight weeks of barely above freezing temperatures, or three weeks of exceptional heat: the numbers come out about right either way. Once enough heat energy is delivered, the ice is gone.

Freeze Thaw Index Graph

So what can we see from this updated graph? The last point on the graph shows that right now, we’re still below freezing most of the time. On the day that the mean temperature goes from below freezing to above*, Sean will draw the vertical upward line that marks the end of winter and place a blue cross on the chart.

Once we reach that point, he’ll be able to estimate our Thaw Index: the number of degree days it might take to melt that much ice.

*For the long term, that is. A single above freezing day does not mark the change of seasons.

But we can already see that this has been a long cold winter. With a freezing index of -1756 degree days, we’re in the same ballpark as last winter. The two winters before that were a lot milder, and you’d have to go back to 2014 to see one that was much worse. That was an ugly winter.

Sean sent along another graph that compares the recent winters in a different way.

Winter Severity Graph

On this plot, each winter gets a different coloured line. Each line ends on the date the mean temperature rose above freezing. This (2019) winter is the dark red line. It goes horizontally after today’s date because we don’t have the whole story yet. We don’t quite know when we’ll switch to thawing and end the line.

That brutal 2014 winter is the grey line at the bottom. We made a lot of ice that winter.

Sean made an interesting point about last winter, represented by the dark blue line. It was leveling off nicely, looked like it was all over, and then things turned cold for three more weeks, which you can see as a late dip in the line that extended it into April.

In summary, this winter was cold enough to make a lot of ice.

There are two things that might tip the balance in favour of an earlier thaw: reports that the ice is not very solid because of frequent snowfalls, and a long-range forecast for warm spring weather.

I’ll start on aerial photography when I have a flight on a  clear day.