April 11, 2018: Science!

I didn’t fly today, so no new aerials. I’ll be talking to Ken O’Neil on Q-104 tomorrow morning, and then I’ll be flying on Friday, so I hope to have fresh photographs up for the weekend.

In the meantime, some historic data, and what it tells us about this year.

First, I heard from Madeleine Dreger. She has a place on Bigstone Bay, and she’s been recording the date of the ice-out there for thirty years. That’s great, because Bigstone is one of the last areas to let go each spring, so her dates are pretty close to the dates I have for Lake of the Woods overall. So I plotted all her numbers as a reflection below my own brick graph. It looks like this:

Brick Graph with Bigstone data corrected

As you can see, with more data, the bell curve is more pronounced. There’s a strong tendency for the ice to go out in late April or early May, but some years are better or worse. Insert ominous music here.

Some people have wondered why I use five-day periods, rather than specific dates. It’s because I’m never flying over the lake at the exact moment the last bit of ice melts. I came close one year, but usually I see ice one day, and none three days later, and I have to guess.

Speaking of guessing, each spring I look at Safety Bay, and when it starts to open up, I begin making regular patrols. That backfired badly this year, because we got to that point in March, and then it turned cold again.

Today I got an email from Sean C., who has a better way. He sent me a really cool graph that shows how the ice-out depends on the severity of the winter and the warmth of the spring. I’ll provide his full explanation, and then I’ll summarize some of the highlights.

Here’s his explanation.

I decided to take a look at some data to see if I could create a forecast of the date we are expecting Ice out on LOTW to see if we run the risk of a spoiled May Long weekend on Corkscrew. I shared it with some friends and they suggested sharing it with you.

I did a Freezing or Heating index over the last 5 years (including the winter of 2013/2014 since it was as bad as bad gets). The analysis is fairly simple. Its just a summation of all the daily mean temperatures through the winter for the freezing index and the same through the summer for the heating index. This data is used to determine how deep frost will penetrate into the ground in the winter as well as the thaw in the summer. I don’t know the correlation with ice depth and its subsequent thaw but the data speaks for itself.

In the attached graph, I plotted the cumulative heating and freezing indices for each season. The red dot is the date which your website has ‘called it’ for each season. Looking at the data, this winter was about as cold as the winter of 2014/2015. The Cyan X represents the date when the daily mean temperature was consistently above 0 which we can generalize as more heat was in the air than cold. So in the spring of 2015, we needed 196 heating index days to get to the ice out date. Using that same assumption we will need roughly 200 days this year. Right now, our daily mean temperatures are still consistently negative. So once we start seeing daily means above 0, it will be easier to forecast but right now I would say it is going to be close. It took from April 7th, 2015 when the mean temps were above 0 until May 3, 2015 to achieve those 196 heating index days which was 27 days. So a safe bet would be that it will take 27 days this year based on the temperatures we have seen. So right now its looking like a close call for may long weekend but as long as we start seeing daily mean temps in the positives in the next week or two, I think we will be ok.

Here are the highlights:

The upward spikes show how long and hot the summer was. 2015 and 2016 were hot summers. 2013, not so much.

The downward spikes show how long and cold the winter was.  2013/2014 was nasty, 2016/2017 was mild. This winter has been cold, more like the former.

The blue X’s mark the date when the temperatures switched over to mostly above freezing, and the red dots show when the ice went out.

Sean used those past dates to work out how long it takes the ice to melt after a winter like this one. See his last paragraph, above. Sean’s calculations do not include such short-term variables as snow-cover, sunshine, wind or rain.

Here’s the thing: we haven’t got our blue X yet this year, because we’re still spending more time below freezing than above. When we do reach that point, we’re still going to need roughly four weeks to open the lake. Let’s hope we can get started soon.


3 thoughts on “April 11, 2018: Science!

  1. Interesting stuff!

    Indirectly, the index does sort of take into account snow cover etc., in that with persistent snow cover (as in 2014 and 2018), it’s much harder to warm to the “blue X” point. These factors also influence the rate of accumulation of “heating index days” leading to breakup.

  2. This is great information. For a new owner on LilyPad and not familiar with past history of “ice-out” dates, this really helps me understand how this lake responds to weather. Great job and thanks to all contributors.

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