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Great Lakes Water Forecasts

This page contains weekly water-level forecasts for the Great Lakes and connecting channels, as well as a six-month forecast bulletin and future scenarios.

weekly great lakes update

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connecting channel depths
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Expected water levels on the Great Lakes connecting channels and the St. Lawrence River are given in inches above (+,0) or below (-,0) low-water datum (LWD,0). LWD is a plane of reference on a navigation chart, also known as chart datum. LWD elevations shown below are given in International Great Lakes Datum, 1985 (IGLD 1985,0). Available water depth is determined for a location by adding (if+) or subtracting (if-) the amount from the above table to the appropriate channel depth shown in the profile connecting channel depths graphic or to water depths shown on National Oceanic and Atmospheric Administration (NOAA) navigational charts.

Depths so determined are representative of a still water surface elevation without being disturbed by wind or other causes. Depths, however, may be reduced or increased as much as several feet for short periods due to these disturbances, or when sections of channels develop shoals. Vessel masters should refer to "Local Notice to Mariners" for extent of shoaling and scattered bedrock projections in all channels.

Six Month Water Level Forecasts


Download Lake Superior .PDF

Download Lakes Michigan-Huron .PDF

Download Lake St. Clair .PDF

Download Lake Erie .PDF

Download Lake Ontario .PDF

Monthly projections of Great Lakes water levels are jointly produced by the U.S. Army Corps of Engineers Detroit District, and Environment and Climate Change Canada over a six-month forecast horizon.

The Great Lakes generally follow a seasonal cycle where during the fall and early winter, water levels decline due to an increase in evaporation as temperatures decline and cold air moves over relatively warm surface waters. In the spring and early summer, water levels typically rise due to increased precipitation and enhanced runoff from snowmelt. The combined effect of precipitation over the lake, evaporation from the lake, and runoff to the lake is referred to as "water supply" or "net basin supply."


Full Bulletin and Summaries

Monthly Great Lakes Water Level Summary

Water levels for the previous year and the current year to date are shown as a solid line on the hydrographs. A projection for the next six months is given as a dashed line. This projection is based on the present condition of the lake basin and anticipated future weather. The shaded area shows a range of possible levels over the next six months dependent upon weather variations. Current and projected levels (solid and dashed lines) can be compared with the 1918-2023 average levels (dotted line) and extreme levels (shown as bars with their year of occurrence). The legend below further identifies the information on the hydrographs.

The levels on the hydrographs are shown in both feet and meters above (+) or below (-) Chart Datum. Chart Datum, also known as Low Water Datum, is a reference plane on each lake to which water depth and Federal navigation improvement depths on navigation charts are referred.

All elevations and plots shown in the bulletin are referenced to International Great Lakes Datum 1985 (IGLD 1985). IGLD 1985 has its zero base at Rimouski, Quebec near the mouth of the St. Lawrence River (approximate sea level).

Click here to view the Monthly Bulletin Great Lakes Update guide.

Future Scenarios

This product is not an official forecast of Great Lakes water levels. This product is meant to illustrate outcomes that would occur under historical weather and water supply condition, with scenarios chosen based on similarities to recent conditions. This tool has been predominantly used to show the possible range of water levels in the upcoming year based on historical hydrologic conditions and water supplies. 

A future-scenarios graphic for Lake Ontario is under development and an experimental version is provided in the water level future-scenarios report.

View Full Great Lakes Water Level Future Scenarios Report

 

Water levels follow a seasonal cycle where during the fall and early winter, the lakes generally decline due to an increase in evaporation as temperatures decline and cold air moves over the relatively warm lake waters. In the spring and early summer, water levels typically rise due to increased precipitation and enhanced runoff from snowmelt. We refer to the combined effect of precipitation over the lake, evaporation from the lake, and runoff to the lake as Net Basin Supply (NBS). This edition of the Water Level Future Scenarios incorporates the projection of water levels if NBS values are like those experienced in the years in which the warmest winters occurred. Ten NBS sequences are incorporated into this analysis to represent the ten warmest winters and are shown by the purple plume shown in the plots. In addition, three of the years within the purple plume have been called out to show the difference in hydroclimate conditions that could occur over the next 12 months – 1998-99, 2012-13, and 2017-18. ​The gray shaded area on the plot represents the full range of possible outcomes using historical sequences of NBS from 1900 through 2023. The most recent coordinated six-month forecast is also shown for comparison.

Explore Great Lakes Water Management

All Great Lakes Water Management data contained herein is preliminary in nature and therefore subject to change. The data is for general information purposes ONLY and SHALL NOT be used in technical applications such as, but not limited to, studies or designs. All critical data should be obtained from and verified by the United States Army Corps of Engineers Detroit District, Engineering and Construction Division, Hydraulics and Hydrology Branch, 477 Michigan Avenue, Detroit, MI 48226. The United States of America assumes no liability for the completeness or accuracy of the data contained herein and any use of such data inconsistent with this disclaimer shall be solely at the risk of the user.

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