April 22, 2018: Graphs

I’ve been thinking about how the time it takes to thaw the lake relates to when we start, and how this year fits the pattern. I pestered Sean C. for some data, and plotted it out as a Floating Bar Graph.

Oldest years are at the bottom, newest at the top. Each year gets a bar that starts on the inflection date (when the mean temperature rises above freezing for keeps) and ends on the date when the lake is ice-free.

You can see two kinds of information here:

First thing, there’s some hope that late thaws can go faster than early ones. Compare 2013 to 2012, for instance. It’s not always true, of course; a lot depends on the temperatures and the ice thickness.

Second thing, it looks like we’re having a crummy year. We’re  certainly off to a late start.

I wasn’t sure how to show 2018, because the thaw’s still in progress, but here’s what I did. Inflection date was April 17. We know there’s still ice today, so that first week is dark blue. It would be extraordinary if the lake thawed in under 20 days, so that span is turquoise. I don’t think we’ll live up to the potential for a really fast thaw, because the ice is thick and the temperatures have been at or below normal. The white stretch with the blue outline is my best guess, which is why it ends with a question mark.

Sean sent me another graph of his own. It’s pretty cool, and it does more to look ahead.

This compares 2018 to best and worst recent years, in terms of how fast we reached enough accumulated warmth for a thaw after a winter like this one. That value is represented by the horizontal line at a Thawing Index of 200. That’s our target for this year.

2004 was slow to warm up. That’s the green line staggering along the lower path. I guess we’re lucky we didn’t have super thick ice that year.

2007 was much better. That’s the red line that shoots up steeply.

2018 is represented by the blue dots, and so far, we’ve been following a good path like 2007’s. We’ve risen from a mean temperature just above freezing to seasonal norms in just a few days. But the weather forecast says we won’t be able to keep up that kind of increase, and suggests we might follow a middle road like the yellow line. If we do, we end up ice-free around May 18.

I’ve been pessimistic about the below-normal temperatures in the long-term outlooks, but Sean’s graph suggests that even with the not-so-great forecast we have, we can still be fully thawed for the Victoria Day weekend.

 

 

April 21, 2018: Satellite Retrospective

Let’s take a look at how this year compares to other recent years. Using false-colour satellite imagery will make it really clear how much of Lake of the Woods was open this time each year.

All these images are from the MODIS camera on Nasa’s Aqua satellite, and are used with permission of Liam Gumley, Space Science and Engineering Center, University of Wisconsin-Madison.

The false-colour images give great contrast between open water, which is black, and hard ice, which is turquoise.

To see a natural-colour satellite image with some of the lakes, bays and islands labelled, click here.

In chronological order, starting with 2014:

This is what Lake of the Woods looked like on April 22 of 2014. That was a hard winter that gave us a thaw in late May. Working from top to bottom, you can see little patches of open water on the Winnipeg River at Kenora, The Elbow by Allie Island, Big Narrows, Whitefish Bay near Sioux Narrows, Flag Island at the North West Angle and the mouth of the Rainy River near Baudette.

2015:

This is April 22 of 2015. That was a normal year with a thaw in early May. Quite a difference: nearly half the ice is gone by this date.

2016:

This is April 19 of 2016. More ice area than 2015, but the ice is darker and weaker. The lake still cleared by early May that year.

2017:

April 21 of 2017. The lake is already almost ice free. This was a warm spring following a mild winter.

2018:

This is April 21 of 2018. The focus is a little soft on this one, but you can see how this year closely resembles 2014. I notice two significant differences between this spring and four years ago. On the negative side, 2014 had open water at the mouth of the Rainy River, at the south end of the lake, and we don’t have that this year. On the plus side, the overall quality of the ice looks weaker this year, especially around Clearwater Bay, Whitefish Bay, and south of Big Narrows.

What happens next will depend mainly on the temperature, but day-to-day weather conditions can also have an effect. The ideal sequence would be rain soon, to remove the snow-cover; then warm sunny weather to melt about half the ice; then strong winds to break up the remainder and smash it against the shore. The worst combination would be fresh snow, cold nights and light winds.

So I note with interest that temperatures are likely to sink back below normal after this weekend, and that Thursday could bring us a mix of rain and snow showers. I’d like the rain to dominate.

A late spring can result in a speedy melt if the May temperatures are warm, but I think the coming weather will be more typical of April, so we may not see the ice go very quickly.

I’m still guessing May 15-18 to be completely ice-free, but I’d feel better with an outlook that included more normal temperatures.

If you’re not already there, don’t forget to visit the Lake of the Woods Ice Patrol home page. See all the posts, plus comments, archives and links.

April 20, 2018: Normal Temperatures

Patchy cloud shadows when I landed Friday evening make it a little hard to judge things on this picture. Click on it to see a larger version that makes things clearer.

Rat Portage Bay is in the middle of the photo and downtown Kenora is in the lower right corner. At first glance, it looks as if all the new April ice might be gone, but a closer look shows that nearly half of it survived an afternoon high of 12°C. There are still patches of recently refrozen surface near the Keewatin bridge, in Kenora Bay, and near the Clarion Inn.

But we can take heart in two things: the snow cover is disappearing, and the weekend should be warm. Our forecast for Saturday and Sunday is for temperatures to reach 12 or 13 degrees, which is normal for this time of year. That should finish melting the recently reformed ice and take a heavy toll on the snow cover. It will be mainly sunny, too, so we might finally see some sunshine reach the winter ice. When I go flying again on Tuesday, I hope to see some advances.

The long-term outlook is still not rosy: it looks as if the end of April will still have some overnight lows dipping down to a few degrees below freezing, and the first days of May are forecast to be cooler than normal, too. So although we will make progress, it may not be rapid.

 

April 19, 2018: Factors

I thought if we saw any change today, it would be on the river, where the current is strong. That did seem to be the case north of Minaki, but closer to Kenora, the changes were less dramatic, so just one photograph today.

Here’s a look at the Dalles. That’s Shoal Lake way off in the upper left. For those of you waiting for things to open up around Myrtle Rapids, not yet.

Yesterday I wrote about Sean’s data-based approach to spring versus my observational one. I got some cool feedback in the comments today, so I’m going to put them up here for everyone to see.

First, this one from Stu Everett on whether strong currents help the thaw go faster.

You mention that the analysis does not take a look at current, and how that impacts the length of time from inflection date to ice out. I took a look at the historical outflows from the LOW on the LOW Control Board site. There are some years around the end of March that have relatively high outflows, and others with low outflows. 2016 had very high outflows (most since 2006), and yet the length of time from inflection to ice out was the longest period shown on the graph. Similarly, 2010 was a higher than normal current (outflow) year, yet it too had a long period from inflection to thaw.

This surprises me, my gut feel was that high current flows would quickly show up in the data as a major influence. Apparently that is not the case, at least according to my admittedly brief review of the data.

However, my observation is that this year is shaping up very like 2014. That year, current flows were a bit higher than normal, and actually were on the increase through April. In contrast, current flows this year were lower than average, and have decreased this month. So, if current has any impact, one could speculate that the period from inflection date to ice out will be longer this year than in 2014, if one controlled for other variables. Given that 2014 was about an average year of 32 days, that would suggest that your estimate of less than 4.5 weeks might be a case of “whistling past the graveyard”. But I share your optimism and hope with all my might that my analysis is flawed…

Then a reminder from Matt DeWolfe about the false-colour images available from the MODIS camera on the Aqua satellite.

I find the MODIS Aqua band quite informative for seeing open water, and perhaps ice thickness. Below you can see much of the Winnipeg River open (as well as Rainy River).

https://worldview.earthdata.nasa.gov/?p=geographic&l=MODIS_Aqua_CorrectedReflectance_Bands721,VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor(hidden),Aqua_Orbit_Asc,AMSR2_Snow_Water_Equivalent(hidden),Reference_Labels(hidden),Reference_Features(hidden),Coastlines&t=2018-04-18&z=3&v=-96.22655332947613,48.32770514383812,-92.53514707947613,50.26129889383812

[cid:image001.png@01D3D7CE.8B9AF720]

MODIS (Aqua) Corrected Reflectance (Bands 7,2,1)

Temporal Coverage: 3 July 2002 – present

False Color: Red = Band 7, Green = Band 2, Blue = Band 1

This combination is most useful for distinguishing burn scars from naturally low vegetation or bare soil and enhancing floods. This combination can also be used to distinguish snow and ice from clouds. Snow and ice are very reflective in the visible part of the spectrum (Band 1), and absorbent in Bands 2 (near infrared) and 7 (short-wave infrared, or SWIR). Thick ice and snow appear vivid sky blue, while small ice crystals in high-level clouds will also appear blueish, and water clouds will appear white.

Water

Liquid water on the ground appears very dark since it absorbs in the red and the SWIR. Sediments in water appear dark blue. Ice and snow appear as bright turquoise. Clouds comprised of small water droplets scatter light equally in both the visible and the SWIR and will appear white. These clouds are usually lower to the ground and warmer. High and cold clouds are comprised of ice crystals and will appear turquoise.

Today’s Aqua image is a bit blurry, so I’ll use yesterday’s false-colour image to show you what he means.

The open water of the Winnipeg River really pops on this picture, and you can see how the river’s main channel is open far beyond Minaki and Big Sand Lake all the way up through Umfreville Lake and beyond. The rusty-looking patch near the south end of the river is Kenora, and the two patches of dark water near it are Safety Bay and Keewatin Channel. The wishbone-shaped patch of open water near the center of the picture is Big Narrows, and the tiny dark patch halfway down the right side is Whitefish Narrows. If you need more help figuring out what you’re looking at, head over to my FAQ page, then scroll down to the bottom to see a natural-colour image with some of the key features on and around Lake of the Woods labelled.

April 18, 2018: More Science!

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.

 

 

April 17, 2018: Warm & Windy

We had sunny weather today, with a high of 7°C this afternoon. Better yet, it was breezy, with winds of up to 20km/hr from the north east.

It wouldn’t be realistic to expect one nicer day to make a big difference, and most of the photographs I took today look just like the ones I took yesterday, so I’ll only put this one up.

This is looking south over Devil’s Gap with Treaty Island stretching from near the center to the right edge. Beyond that, lots of ice out by Rogers Island, Town Island and so on. Zoom in, and you can see the ice roads still look pretty solid. Rat Portage Marina is visible at the lower left, (partly obscured by the digitally distorted propeller blade) and there’s still ice all around the docks.

However, to my eye, the ice looks distinctly more gray today. It’s not glaringly obvious in the photographs, but with the picture above you can zoom in on the lower right corner to check out the ice surface around Gun Club Island, and you might agree that it looks patchier.

Terra Satellite got a clear image today, so I have updated the satellite link. Usually the first patch of open water on Lake of the Woods big enough to “see from space” is down by Baudette, Minnesota, where the Rainy River spills into the lake and creates a dark patch on the south shore. That hasn’t happened yet.

The temperatures tomorrow are forecast to dip slightly, which will likely put Wednesday’s mean daily temperature right at the freezing point, but from Thursday on, we should be consistently trending warmer through to the end of April. Not fabulously warm, or even normal, but almost always above freezing, even at night.

That should mean we’re switching from making ice to melting ice. Finally.

 

April 16, 2018: Same Old

Today’s pictures are almost identical to Friday’s. We came in to Kenora on the same flight path, and nothing has changed.

When there’s a bit more open water developing, I’ll make a greater effort to range further out over the lake. For now, there’s nothing new to see.

Winnipeg River.

The Dalles, Myrtle Rapids. No significant change. In the distance, at the top of the picture, Shoal Lake, (on the right) and the US side of LotW (top center) are still pure white.

The powerline crossing.

No change.

Kenora to Keewatin.

No change.

Safety Bay.

No change. Note that you still cannot get a boat from Safety Bay to Channel Island, and that even the new ice near the Keewatin bridge has not melted.

However, I have high hopes for things to take a turn for the better tomorrow. Right now the forecast is calling for a high on Tuesday of about 7°C, and although temperatures sink a little on Wednesday, by the end of the week, we might be staying at or above freezing overnight. If that holds true, we should start to turn the corner.

Another guest contribution! Here’s a chart from John Harbottle, giving the ice-out dates he’s recorded for Kendall Inlet and Clearwater Bay.

John points out that the dates correspond well with the Bigstone Bay data from Madeleine Dreger. That makes sense to me, because both Bigstone and Clearwater are rather late melters.

Neither satellite has captured a cloud-free picture of Lake of the Woods since April 13, so I have not updated the link. Reminder: the sidebar and links do not appear in the emails, they are a feature of the full Ice Patrol website.

I am flying tomorrow, but I don’t really expect one warmer afternoon to make a visible difference. And remember, daytime highs in the single digits are still below normal for this time of year. But maybe we’ll lose some of that snow cover by the weekend- that would be nice.