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