LEVELnews: Great Lakes and St. Lawrence River water levels, September 2019

Volume 27, Number 9

August saw all the Great Lakes at near or above record high levels

With near or above record high water levels on all the Great Lakes combined with a greater probability of large storms and winds in the coming months, the risk continues for accelerated coastline erosion and flooding to low-lying areas. For local sources of information on this, see the following sections of this edition of LEVELnews.

During the month of August, all of the lakes were either at their highest recorded levels (lakes Superior and Erie) or their second highest (lakes Michigian-Huron and Ontario), based on the period of record from 1918 to 2018.  Interestingly, at the same time, most of the lakes also experienced very large declines in their water levels including Lake Erie which tied its largest August decline on record, and Lake Ontario which had its second largest August decline on record.  This is the time of the year when all the lakes typically decline going into the fall and winter.

Not surprisingly, the beginning-of-September levels are also very high in all the lakes, with Lake Erie the only one setting a record by starting the month 8cm higher than the previous record level back in 1986.

With average meteorological conditions, water levels in the Great Lakes basin are expected to demonstrate their typical seasonal decline over the next few months. How quickly they decline is dependent on the weather and how wet or dry it will be over the coming weeks and months.

If conditions are average, the levels in Lake Superior and Lake Erie have the potential to remain near record seasonal highs while Lake Michigan-Huron and Lake Ontario levels would continue to be well above average, but not in record territory. With the high current lake levels, wetter than average conditions could result in more recordbreaking levels. On the other end of the scale, even with very dry conditions all the lakes would remain above average into the fall.

Fall water warnings

The fall and winter are seasons that can bring higher waves and storm surges on the Great Lakes. Winds blowing across long open water sections, or fetch, can cause large waves and push water levels up on the downwind side of the lakes. As shown in this graph of significant wave heights from a buoy in eastern Lake Ontario, typically waves increase during the fall and peak in November.

Data source - National Data Buoy Center
Long description

The figure shows the monthly maximum and minimum significant wave height for a buoy in eastern Lake Ontario. The maximum heights vary from 2 to 3 metres from April to August and then increase to 3.5 metres in September, 5.9 metres in October, 7.6 metres in November, and down to 3.5 metres in December. The minimums are 0.0 metres for all months except November which is at 0.6 metres. The averages are based on measurements taken between April of 2002 and November of 2008.

The largest waves occur on Lake Superior, where the maximum wave heights may approach 9m, and the largest storm surges occur on Lake Erie, with the largest being about 2.5m. Although waves and storm surge are usually well below these maximums, they can create rapid changes in water levels. Anyone undertaking activities on or along the shores of the Great Lakes should be aware of potentially dangerous conditions during high winds. As well, in the coming months, the above-average levels of the lakes could increase the potential of erosion of some shorelines, especially steep shorelines exposed to waves that are made up of silts, sands, gravels and cobbles. Although erosion around the Great Lakes can result in significant changes to the shoreline that can impact property and activities around the lakes, it is also a naturally occurring process that helps support the ecosystem of the Great Lakes.

Information on flooding

Great Lakes water levels are hard to predict weeks in advance due to natural variations in weather. To stay informed on Great Lakes water levels and flooding, visit the Ontario flood forecasting and warning program web site.

Local flood watches and flood warning information are issued in Ontario by Conservation Authorities or Ministry of Natural Resources and Forestry district office.

Additional information can also be found at the International Lake Superior Board of Control web site, and the International Lake Ontario–St. Lawrence River Board web site.

More information is also provided in the “Water levels forecast” section at the end of this newsletter.

Information on current water levels and marine forecasts

With lake levels changing day-to-day the Government of Canada Great Lakes water levels and related data website provides a source for web sites on up-to-date Great Lakes water levels.

Daily levels: Current daily lake wide average levels of all the Great Lakes (pdf) is an average taken from a number of gauges across each lake and is a good indicator of the overall lake level change when it is changing relatively rapidly due to the high precipitation recently experienced.

Hourly levels: Hourly lake levels from individual gauge sites can be found at the Government of Canada Great Lakes Water Level Gauging Stations website. These levels are useful for determining real-time water levels at a given site, however it should be noted that they are subject to local, temporary effects on water levels such as wind and waves.

Marine forecasts: A link to current Government of Canada marine forecasts for wave heights for each of the Great Lakes can be found on the Great Lakes water level and related data web page under the “Wave and wind data heading”. Current marine forecasts for lakes Superior, Huron, Erie and Ontario are available by clicking on the link of the lake you are interested in. To view a text bulletin of recent wave height forecasts for all of the Great Lakes.

August monthly levels

All the Great Lakes had well-above-average monthly-mean water levels in August, with lakes Superior and Erie recording a value above or tied with a record-high value (1918–2018).

Lake Superior was 32cm above its period of record (1918–2018) August monthly mean water level and 21cm above its level in August of last year. This value is tied with 1952 and 1950 for the highest values for the month.

Lake Michigan–Huron’s monthly mean level in August was 76cm above average, 37cm above last August’s level. This puts it at the second highest August level, 7cm below the value in 1986.

Lake Erie’s monthly mean level was 75cm above average, 30cm above it level during August 2018 and 19cm higher than the previous record set in 1986. This is now the highest meanmonthly level on record.

Lake Ontario’s July monthly mean level was 64 cm above average and 62 cm higher than a year ago. You have to go back to 1947 to find the year that had a higher level for August, which was 5cm higher than this year.

Great Lakes water level information: August 2019 Monthly Mean Level
Lake Compared to Monthly Average
(1918–2018)
Compared to One Year Ago
Superior 32cm above 21cm above
Michigan–Huron 76cm above 37cm above
St. Clair 80cm above 32cm above
Erie 75cm above 30cm above
Ontario 64cm above  62cm above

Lake level changes

Lake Superior’s levels declined by 4cm in August, while the lake typically goes up by 1cm between the beginning of August and September.

Lake Michigan–Huron went down by 10cm, which is much more than the average decline of 4cm.

Lake Erie’s level declined by 16cm, double its average fall of 8cm and tied with 3 other years for the largest August to September decline on record.

Lake Ontario went down by 34cm, more than double its average decline of 14cm and the second largest on record, only 1cm less than the record decline in 2017.

Beginning of September lake levels

At the beginning of September, Lake Erie had a record high level for that time of the year, with the other lakes all well above average.

Lake Superior’s beginning-of-September level was 30cm above average (1918–2018) and 18cm higher than September 2018. This beginning-of-September level is the third highest beginning-of-month level, just 1cm below 1952 and 2cm below 1950.

Lake Michigan–Huron’s beginning-of-September level was 73cm above average and 30cm higher than its level at the same time last year. Also the third highest in the period of record, this time 8cm lower than 1986 and 1cm lower than 1973.

Lake Erie was 79cm above average at the beginning of September and 27cm higher than the same time last year. This sets a new record by 8cm over the beginning-of-September record set in 1986.

Lake Ontario’s level at the start of September was 54cm above average and 52cm higher than the water levels last year. This is a beginning of month level we have not seen since 1952.

At the beginning of September, all of the lakes were at least 64cm above their chart datum level.

Great Lakes water level information: Beginning-of-September 2019 Level
Lake Compared to Beginning-of-Month Average (1918–2018) Compared to One Year Ago
Superior 30cm above 18cm above
Michigan–Huron 73cm above 30cm above
St. Clair 79cm above 27cm above
Erie 72cm above 27cm above
Ontario 54cm above  52cm above

Water levels forecast

Relative to their beginning-of-September levels and with average water supplies for this time of year, all the lakes would be expected to begin or continue their seasonal decline.

The forecast for Lake Superior indicates that if the lake receives average water supplies it will start its seasonal decline starting in September. However, with extremely wet conditions, it could again start to approach record values for the next few months.

Lake Michigan-Huron would continue its seasonal decline in September if we experience average water supplies. Only under very extremely wet conditions would levels return to their near-record values. However, even If we experience very dry conditions, the levels will continue to be well above average going into the fall.

As it starts the month at a record high level, average conditions for Lake Erie would still possibly result in a record-high level for September. Consequently, wet conditions would keep the level above records values while even dry water supplies would still continue to keep the levels well above average.

Lake Ontario has fallen enough below its record values that only extremely wet conditions would result in those record levels being approached again. With average conditions, the seasonal decline in the lake levels will continue into the fall while only extreme dry conditions would allow the lake to approach average levels by the end of the year.

For more information on the probable range of water levels consult the September 2018 edition of LEVELnews.

For a graphical representation of recent and forecasted water levels on the Great Lakes, refer to the Canadian Hydrographic Service’s monthly water levels bulletin.

August precipitation over the Great Lakes a,b
Lake %
Great Lakes Basin 76%
Lake Superior 69%
Lake Michigan-Huron 68%
Lake Erie (including Lake St. Clair) 103%
Lake Ontario 93%
August outflows from the Great Lakes a
Lake %
Lake Superior 134%
Lake Michigan-Huron 130%
Lake Erie 128%
Lake Ontario 141%

a As a percentage of August long-term average.
b United States Army Corps of Engineers

Note: These figures are preliminary.

More information

Frank Seglenieks (Editor)
Boundary Water Issues
Meteorological Service Canada
Environment and Climate Change Canada
Burlington ON L7S 1A1
Tel.: 905-336-4947
Email: ec.LEVELnews-infoNIVEAU.ec@canada.ca

Rob Caldwell
Great Lakes-St. Lawrence Regulation Office
Meteorological Service Canada
Environment and Climate Change Canada
111 Water Street East
Cornwall ON K6H 6S2
Tel.: 613-938-5864

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