We had another warm day. One photo:
Looking west with Shoal Lake on the horizon. Town Island is at the left, Shragge’s Island is closest to the center of the picture, Devil’s Gap is towards the lower right. No real expansion of the open water, but some further loss of snow cover.
Now an update from Sean C. He and I agree that as of yesterday, our Mean Daily Temperature is above freezing.
First, his updated graph that finally gives 2018 a blue X, marking yesterday as this spring’s “Inflection Date” when we stopped making ice and started melting it.
The downward spikes indicate the length and severity of the winter, and now that we’re saying this one’s over, we can compare it to other recent winters. Not as severe as 2014, but worse than most. You can even make out our early April cold snap on the profile: it’s that tiny downward jab at the tip of the spike.
Next, Sean took a look at all the winters since 2003, and graphed them against each other.
For this graph, he lined up all the Inflection Dates together, at Day Zero, and then looked at how long it took to reach the same thawing index. The horizontal red line is his estimate of how much heat we should need to thaw the lake after a winter like this one. In the best case, it took 20 days to reach the equivalent of a full melt. The worst year took almost three times as long: 54 days.
By applying the average of 32 days, Sean found himself looking at an estimate of getting ice free on May 18th, the Friday of the Victoria Day weekend. In other words, right down to the wire for places like Clearwater Bay and Bigstone Bay.
Warning: this mathematical average does not directly factor in such things as abnormal sunshine, current, or snow cover.
I had a question: “Won’t it go faster in May than if we started in March?” You can now stop calling me Ice Captain and start calling me Captain Obvious. Sean obliged me with this graph.
He knocked it off in a hurry, so it doesn’t have a pretty name, but it plots Thawing Index on the left edge versus Inflection Date across the bottom. The individual blue dots represent sample years and the diagonal line is a best fit for the overall trend. It shows, with a lot of variation from year to year, that the later you start the thaw, the faster the ice goes.
This fits with my old—but overly simple—notion that the thaw tends to even out. Keep in mind that until this year, I worked almost entirely from my aerial view of how much open water there was, and only regarded temperature as an influence on an inevitable process, rather than a fundamental factor. Sean has changed the way I look at it. Remind me to update the FAQ.
If we take into account both the thick ice from the cold winter, and the faster thaw due to starting late in the year, we get a rather more encouraging timeline. Instead of the 32 day average to melt a cold winter’s ice, we get a number that could be as low as 20 days to melt this thickness of ice when we start after mid-April.
That would put us at May 8, which is close to my estimate from before the cold snap. Hmm.
Neither Sean nor I have faith that that’s how it will play out. He remarked that, “…past performance doesn’t guarantee future profits.” He probably worries about how close that comes to the fastest thaw in his data. I don’t like how it fails to factor in a forecast for two more weeks of mean temperatures at or below normal.
Let’s allow more than three weeks, but less than four and a half. Four weeks would give us a lake entirely free of ice just days before the long weekend. Fine print: no guarantee is expressed or implied. This offer does not apply to Shoal Lake. (Shoal Lake usually runs a few days later.)
Cheer up; even if it’s close, most lake dwellers don’t need the whole lake to be open.