Lake Superior experiences atypical July decline due to very dry water supply conditions
During the month of July, the Great Lakes Basin experienced the following:
- The mean monthly water level of Lake Superior was at its average level, while Lake Michigan-Huron was above average. Lake Erie remained well above average, while Lake Ontario was very close to average.
- Lake Superior experienced extremely dry water supply conditions, while Lake Michigan-Huron experienced wet water supply conditions (a combination of the precipitation, evaporation, and runoff). Lake Erie experienced very dry conditions, while Lake Ontario received extremely wet water supply conditions.
- In July, Lake Superior received much lower than average precipitation, while Lake Michigan-Huron received close to average precipitation amounts. Lake Erie received close to half of its average July precipitation, while Lake Ontario received much higher than average precipitation.
- Lake Superior experienced its sixth largest July water level decline on record. Lake Michigan-Huron experienced a greater than average rise, while Lake Erie experienced a higher-than-average monthly decline. Lake Ontario rose when it typically declines at this point in the year.
This is the time of year where all the lakes except for Lake Superior have typically peaked and have started their seasonal decline.
With water levels remaining above average on some lakes and the possibility of large storms and winds, low-lying areas are at risk for accelerated coastline erosion and flooding. For current information and forecasts, please refer to the sources listed at the end of this newsletter.
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1 Water levels are referenced to International Great Lakes (Vertical) Datum 1985 (IGLD85). For more information, please visit International Great Lakes Datum Update – Great Lakes Coordinating Committee.
1 Lake level changes are based on the differences in levels at the beginning of the month, not the monthly average levels.
1 At the beginning of August, all the Great Lakes were at least 30 cm above their chart datum level. Chart datum is a reference elevation for each lake that provides more information on the depth of water for safe boat navigation on the lakes. For more information, please visit Low Water Datum – Great Lakes Coordinating Committee.
2 Water levels are referenced to International Great Lakes (Vertical) Datum 1985 (IGLD85). For more information, please visit International Great Lakes Datum Update – Great Lakes Coordinating Committee.
Water levels forecast
Lake Superior ended the month very close to its average level and is expected to remain just below average under typical water supply conditions. If there are very wet water supply conditions, lake levels could move above average, while very dry conditions would result in lake levels moving further below average.
Lake Michigan-Huron is expected to remain above average under typical water supply conditions, although wetter than average conditions could result in sustained higher than average levels. Drier than average conditions could result in lake levels falling below average within the next few months.
Lake Erie is expected to stay above average under most water supply scenarios. It would take very dry water supply conditions for lake levels to fall below average by the end of the year.
Lake Ontario water levels are expected to remain near average under typical water supply conditions. However, wetter than average water supply conditions may result in above average lake levels, while drier than average water supply conditions would result in the level moving below average.
For more information on the probable range of water levels, consult the LEVELnews note on projections.
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.
1 As a percentage of long-term average (LTA).
2 Environment and Climate Change Canada – Canadian Precipitation Analysis System. For more information, please visit: Technical documentation: Regional Deterministic Precipitation Analysis
3 <5% extremely wet; <25% very wet; <45% wet; 45-55% average; >55% dry; >75% very dry; >95% extremely dry.
4 Please refer to the LEVELnews – What is net basin supply for a description of net basin supply.
Note: The figures contained in this report are provisional and are subject to change. Data are calculated from the best available observations at the time of posting.
Flood information
With water levels remaining high on some lakes, there is a risk of flooding. Great Lakes water levels are difficult to predict weeks in advance due to natural variations in weather. To stay informed about Great Lakes water levels and flooding, visit the Ontario flood forecasting and warning program.
Additional information can also be found on the International Lake Superior Board of Control website, and the International Lake Ontario–St. Lawrence River Board website.
Information on current water levels and marine forecasts
Monthly levels: Fisheries and Oceans Canada produces the Monthly Water Level Bulletin for the Great Lakes and Montréal Harbour. On this page you will find a link to the full bulletin PDF. This publication complements the information provided by LEVELnews monthly.
Daily levels: Current daily lake-wide average levels of all the Great Lakes are available at Great Lakes - Daily Water Levels for This Month in Meters. The daily average water level is taken from several gauges across each lake and is a good indicator of the overall lake level when it is changing relatively rapidly due to recent high precipitation.
Hourly levels: Hourly lake levels from individual gauge sites can be found at the Government of Canada Great Lakes Water Level Gauging Stations Map. 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: Visit the “Wave and wind data” section of the Great Lakes water levels and related data webpage for marine forecasts and wave heights. Current marine forecasts for Lakes Superior, Huron, Erie and Ontario are available as well as text bulletins of recent wave height forecasts.
For more information
Frank Seglenieks (Editor) and Nicole O’Brien
Boundary Water Issues
National Hydrological Service
Meteorological Service of Canada
Environment and Climate Change Canada
Burlington, ON L7S 1A1
Email: LEVELnews-infoNIVEAU@ec.gc.ca
