Yesterday I said the weak ice between Scotty Island and Whiskey Island would be gone overnight. Wrong! Garry Hawryluk passed overhead on a WestJet flight at 6:00 this morning, and managed a few pictures at dawn. The light was poor, so I’ve enhanced the contrast on this one to make the ice more visible.
What I like about this photo is it shows the full span of that ice sheet south of the Barrier Islands. But if you look just above the big expanse of ice, you can see that the small patch in the Manitou survived the night. It did dip below freezing last night, but I think a bigger factor was that the wind died out: without wave action, the candled ice did not break up or blow away.
My own nefarious plan was to hold off on taking pictures until this afternoon, so I could say, “it was gone when I looked.” Unfortunately, it was still hanging on at 3:00pm.
This picture is centered on Town Island. Click on it to see a larger image, and click on that to zoom in, and you can see that small pans of ice still persist on the Manitou.
At full magnification, you can also see a boat passing by Lunny’s Island. The water is so smooth you can trace the wake all the way back to the Hades!
This picture shifts over to the left to show more of Bigstone Bay and Hay Island. Zoom in on this one and you can see a tiny forlorn patch of ice clinging to Needle Point, just left of the center of the picture. But the real reason I took this photo is I wanted to show the larger sheet of ice in the distance. The top right corner of the picture shows the area south of East Allie Island, and that big expanse of ice there is still, well, big. It looks set to hold on a bit longer.
Now that the thaw is almost complete, Sean and I are looking forward to finishing up our graphs for 2018.
Here’s Sean’s latest version of the prediction graph.
We reached a Thaw Index of 200 today, which Sean guessed (several weeks ago!) would be enough accumulated heat to melt all our ice. It turned out to be a very good guess, especially for a first attempt. Sean used temperature data from past years to work out a relationship between how cold a winter was and how much warmth it takes to melt the ice. That didn’t give him a magic number, it gave him a range. He still had to choose whether this year’s thaw would be rapid or sluggish. He went with a swiftish prediction, and chose a thaw index of 200 as his best guess. (A thaw index of 200 means that starting on the day the temperature averages above freezing, we add each day’s mean temperature to a total. When it adds up to 200, we hoped to be ice free.) Because it was late in the season, I also felt that the thaw would be fairly rapid, but it looks as if the ice won’t be 100% gone until we climb a bit higher than 200.
Remember, my method in previous years was to take aerial photographs and compare them to my archived pictures, and look for the ice to melt at roughly the same pace as those previous years. In other words, I didn’t even try to factor in the forecast, unless it called for a significant run of good or bad weather.
The trick with using long-term weather forecasts to graph mean temperatures in advance is: they’re forecasts, and they go wrong. This April, forecasts were calling for miserable weather. And they were right, at first. Then as May arrived, we started to get much warmer weather than predicted. Changes to the weather forecast meant changes to the ice-out date, but not to the desired index.
I won’t be flying again until Monday. Will I find any ice at all by then? We’re looking at a warm weekend. I’m guessing not.