May 4, 2018: Updated Graph

I’m out of town for the weekend, so no new pictures, but I did get an updated graph from Sean.

May4

The actual daily mean recorded by Environment Canada is  is shown as the string of blue dots. Notice how close it is to the yellow line, which is Sean’s prediction based on the weather forecast. Nailed it!

That means we’re staying on track for a fast thaw, and if we keep it up for another week, we’ll be ice free!

A note on how this prediction works: Sean starts his graph on the day when the average temperature (daily mean) goes above freezing for the season. False starts in March don’t count, so that happened on April 17 this year.  Then he looks back at how cold the winter was to get an idea how thick the ice is, and he uses data from years with similar winters to estimate how many warm days we’ll need to melt it.

This year, he estimated we’d need a “thaw index” of 200. Last Sunday, when we hit 25 degrees, we had a mean temperature of 16, so he adds 16 points towards our target. On Tuesday, we had a cold day, and only managed to add two and a half points.

The initial guess, based on an old mid-April forecast that turned out to be pessimistic, (dashed yellow line) was that we’d rack up the desired index of 200 by May 18. That’s reasonable: one month to go from above freezing to fully thawed is realistic for a late spring.

The fastest spring thaw in recent years was 2007, and is represented by the red line on the graph. It took just three weeks. The weather forecast we had in April didn’t look that promising.

But now we are getting close to having a thaw that fast! Sean’s revised estimate, worked out when the May forecast called for warmer temperatures, is that we might be ice free by May 11. That would be 24 days, compared to 20 in 2007. That’s still a forecast, not a guarantee, but we’re staying on track so far.

The Victoria Day weekend is no longer in jeopardy, and we have a good chance of the lake being entirely open for next weekend.

Boat access to islands close to Kenora, such as Town Island and Scotty Island, should now be just days away.

7 thoughts on “May 4, 2018: Updated Graph

  1. Tim,
    Excellent work on your part and Sean’s. I was just wondering if you had any idea of what the average ice thickness would be at this point. I’m sure that it probably would vary from location to location. And how does ice thickness fit in with the final ice free date? Or is it possible that even after ice out date, we could still see small areas of ice in shaded coves or sheltered areas?

    Chicago John

    • That’s a good question about the ice thickness, and I have no idea. How would we measure it? An air-boat with an auger?
      The second part is easier to answer. I don’t call ice-out until I think it’s ALL gone. 100%. If I can any ice at all from the air, I give it another day. The only doubt arises when I can’t fly on the fateful day, and have to guess.

  2. The north east end of Welcome Channel is almost ice free this morning. Yesterday’s sun and wind broke up the honeycombed ice very quickly.
    We should be seeing boats from town today or tomorrow.

  3. Any chances or a Bare Point/Lunny Island
    Site Shot coming up soon
    Can’t wait to get out there

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