I have always enjoyed nature and in particular, I love watching the sky, there is so much to see and I always want to know "why" things happen.
By: Tom Niziol , 5:09 PM GMT on April 25, 2014
One of the most talked about stories of this past winter and spring has been the record ice cover for this time of the year on the Great Lakes. It has been an exceptional year to say the least. This year the lakes attained their highest percentage of ice cover on March 6, 2014 when they reached 92.2% coverage. The only year since modern satellite-derived records began back in 1973 that achieved a higher percentage of ice cover was in 1979 when it reached 94.7%. In the figure below I show a comparison of the maximum ice cover for this season and the ice cover on April 24, 2014.
Below is a graph which shows the maximum ice cover each season on the Great Lakes from 1973 through 2013. As you can see, in 1979 the Great Lakes achieved a maximum ice cover of 94.7% The lakes also reached well over 80% during several other seasons including 1994 and 1996.
This year has been exceptional not only in the maximum ice cover but the extent of ice cover so late in the season. Looking over the modern records, I found more ice on the Great Lakes in mid-April than in any previous season since 1973 including 1979 as shown below. The existence of significant ice on the Great Lakes so late in the season has a significant impact on the start-up of the commercial shipping season. It also delays the pre-season preparations for recreational boating such as the deployment of temporary docks. Here is a comparison of the ice cover in Mid-April for the seasons since 1973 which attained highest percentage of ice cover at some point in the winter. As you can see, mid-April of 2014 has much more ice cover than previous high ice years.
Based on the fact that we have more ice over on the Great Lakes at this time of the year than other high ice cover seasons, I wondered if the temperatures going into the Spring this year were colder than those for other high ice percentage years. So I took 6 cities around the Great Lakes including Duluth, Marquette, Chicago, Detroit, Cleveland and Rochester and averaged out their daily March through Mid-April temperatures for all of those years as a proxy for Great Lakes Region temperatures, which I call “IceTemp”. When I compared the 4-month time frame to other high ice years, 1979 and 1994 were quite a bit warmer, 1996 was just a tad colder overall for the 6-city average as shown below.
As a result, in each of those years the ice cover melted away more quickly in March than the 2014 season and in 1996 the maximum ice concentration never quite made it as high as this year. Below I constructed a graph of the weekly progression of ice cover for each of the high ice seasons. You can see how this season’s ice cover refuses to melt away as quickly as other high ice years.
In reviewing the ice cover data from 1973-2013 I wondered if we could somehow go back farther to determine historically what this year has been like compared to previous years. There is no direct data available since back then there was no way of assessing ice coverage over the Great Lakes without satellite or aircraft. However there is a wealth of temperature data from stations around the Great Lakes going back well over 100 years, don’t forget, our nation’s inaugural weather service began in the Great Lakes Region back in 1871. Modelling studies have been done that derive historical ice cover based on a parameter called “freezing degree days” (Richards 1964, Assel 1990). Though nowhere as rigorous, I calculated the average monthly temperature for the 6 cities I outlined above on the Great Lakes in the December through March time frame for each season back to 1876 as a very rough proxy for maximum ice cover.
There are a few years with missing data from at least one of the six locations in the dataset. That being said, with the exception of 1885, 2014 has been the coldest December through March period on record when those 6 cities stats are combined. Other years that come close to the 2014 temperature include 1904 and 1912.
On a side note, 1885 must have been an exceptional ice cover year. I found it interesting therefore to learn of a fascinating story about a shipwreck that was a result of ice cover on Lake Michigan. 1885 was the coldest 4 month period (December-March) on record for the combined 6-city set I outlined, only rivaled by 1904 and this past winter. Ice built up quickly that year and in early February a vessel named the Michigan became stranded in the ice. After nearly 40 days the crew had to abandon the ship and head across the ice to a rescue tug that also became stranded in the ice pack. The hardy crew from the Michigan finally hiked to shore and skied the rest of the way back to the comfort of heat and food. The account, reminiscent of the Shackleton Expedition in the Antarctic in 1914 is beautifully retold by Valerie Olson Van Heest in this link IceBoundFound.
It would be great if Mother Nature would cooperate and provide enough Spring warmth to melt the rest of the ice away on Lake Superior and Erie soon. However, the 6 to 10 day temperature outlook from NOAA suggests that below normal temperatures are likely across the Great Lakes Region. Stay tuned, the official start of summer is less than 8 weeks away.
ASSEL, R.A. An ice-cover climatology for Lake Erie and Lake Superior for the winter seasons 1897-1898 to 1982-1983. International Journal of Climatology 10:731-748 (1990).
RICHARDS, T. L., 1964: THE METEOROLOGICAL ASPECTS OF ICE COVER ON THE GREAT LAKES*. Mon. Wea. Rev., 92, 297–302
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