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

Volume 27, Number 8

All Great Lakes were near or above record-high levels through July

With near or above record high water levels on all the Great Lakes the risk continues for accelerated coastline erosion and flooding to low lying areas continues. For local sources of information on this, see the following sections of this edition of LEVELnews.

Water levels on Lake Ontario and Lake Erie slowly declined through July after reaching their annual peak levels in June, which were all time record highs on both lakes (based on the period of record 1918-2018). While declining, levels on both lakes are still above record levels for this time of year. Lake Michigan-Huron and Lake Superior rose slightly through July and remained near or above their record levels as they approach their annual peaks which typically occur later in the summer.

During July, all of the Great Lakes had well-above-average monthly-mean water levels with lakes Erie and Ontario coming in at over 10 cm more than their record-high values. Lake Superior was 4 cm above its record-high and Lake Michigan-Huron was just 3 cm below its record-high value.

At the beginning-of-August, lakes Superior, Erie and Ontario all had record high levels for that time of the year, while Lake Michigan–Huron’s beginning-of-August level was just below its record high value. In particular, not only was Lake Superior’s beginning-of-August level 35 cm above average, it was the highest beginning-of-month level for any month in the period of record.

If we experience 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 Erie and Lake Ontario would remain near record seasonal highs while Lakes Superior and Michigan-Huron levels would start to decline from these record high levels. If we see much wetter than average conditions more record breaking levels could be seen, however even with very dry conditions all the lakes are forecasted to remain above average into the fall.

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.

July monthly levels

All the Great Lakes had well-above-average monthly-mean water levels in July and lakes Superior, Erie and Ontario had record-high values (1918–2018).

Great Lakes water level information:
July 2019 monthly mean level
Lake Compared to monthly average (1918-2018) Compared to one year ago
Superior 35 cm above 21 cm above
Michigan-Huron 79 cm above 39 cm above
St. Clair 84 cm above 33 cm above
Erie 80 cm above 31 cm above
Ontario 79 cm above 74 cm above

Lake level changes

Beginning-of-August lake levels

Great Lakes water level information:
beginning-of-August 2019 level
Lake Compared to beginning-of-month average (1918-2018) Compared to one year ago
Superior 35 cm above 22 cm above
Michigan-Huron 79 cm above 40 cm above
St. Clair 86 cm above 35 cm above
Erie 80 cm above 34 cm above
Ontario 74 cm above 72 cm above

Water levels forecast

Relative to their beginning-of-August levels and with average water supplies for this time of year, Lake Superior is expected to rise slightly over the month of August, while lakes Michigan-Huron, Erie and Ontario begin or continue their seasonal decline.

Based on beginning-of-August conditions, the forecast for Lake Superior indicates that if the lake receives average water supplies it will be near seasonal record levels for August, but will start its seasonal decline starting in September. With average water supplies, the level would remain well above average, but it would take extremely wet conditions in order to approach record values for the rest of the year.

Lake Michigan-Huron is expected to start its seasonal decline in September if we experience average water supplies, coming down from the recent near-record values. With these average water supplies the levels will continue to be well above average for the rest of the summer and into the fall. Only under very extremely wet conditions would levels return to their near-record values.

Although Lake Erie has peaked for the year, it will most likely continue to experience above record levels for the next few months even if we see drier than average water supplies. Going into the fall season, only extremely wet conditions will see near record high levels while average to dry water supplies will continue to keep the levels well above average.

Lake Ontario is also likely to remain near record levels throughout August and after that, only wet water supply conditions will keep the levels near the record highs. For the rest of the year average water supplies would keep the levels above average with only extreme dry conditions bringing the Lake Ontario level close to average.

For more information on the probable range of water levels consult the July 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.

July precipitation over the Great Lakes a,b
Lake %
Great Lakes Basin 81%
Lake Superior 82%
Lake Michigan-Huron 73%
Lake Erie (including Lake St. Clair) 110%
Lake Ontario 85%
July outflows from the Great Lakes a
Lake %
Lake Superior 138%
Lake Michigan-Huron 128%
Lake Erie 129%
Lake Ontario 140%

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

Note : These figures are preliminary.


For 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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