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Great Lakes Basin Conditions

This page provides recent basin conditions with tabs for net basin supply, precipitation, evaporation, runoff, snow water equivalent, ice cover, and surface water temperature data. This page also provides long-term basin trends for lakes Erie, Michigan-Huron, Ontario and Superior. 

Recent Basin Conditions

Net Basin Supply Conditions

 

Net basin supply (NBS) is the primary driver of Great Lakes water levels. NBS represents the total contribution of water to each lake, excluding inflows from upstream lakes, outflows to downstream lakes, and diversions into or out of the lakes. In other words, NBS represents the net influence of precipitation over the lake, runoff from a lake's watershed into the lake, and evaporation from the lake's surface. The graphic displays a plot of NBS over the past 5 years relative to long term average NBS.

Average Precipitation

 

The graphic provides basin-wide precipitation for the past 5 years relative to long-term average.

Access additional Great Lakes precipitation data:
Average Evaporation

 

Evaporation is typically highest during the late fall and early winter, when the air temperature is much colder than the surface water temperature. Evaporation is difficult to estimate, due to the lack of observations across the surfaces of the Great Lakes. The graphic provides simulated evaporation rates for the past five years from the large lake-thermodynamic model relative to long-term average.
Average Runoff

 

Runoff to the Great Lakes is typically highest during the spring, when melting snow combines with liquid precipitation, leading to increased streamflow. The graphic shows simulated runoff rates for the past five years from the large basin-runoff model relative to long-term average.
Average Snow Water Equivalent

 

The graphic shows snow water equivalent data from NOAA's National Operational Hydrologic Remote Sensing Center (NOHRSC) aggregated to Great Lakes basins.

Click here to view additional gridded snow water equivalent data from NOAA's NOHRSC.
Average Ice Cover

 

The graphic provides recent and historical ice cover compiled from data from NOAA's Great Lakes Environmental Research Laboratory.

Click here to view historical, current, and forecasted ice conditions for the Great Lakes from NOAA GLERL. 
Average Surface Water Temperature

 

The graphic provides recent and historical surface water temperatures compiled from data provided by NOAA's Great Lakes Environmental Research Laboratory (GLERL).

Click here to view additional recent and historical surface water temperatures for the NOAA GLERL.

Long-Term Basin Trends

This section includes monthly and annual long-term trends in net-basin supply (NBS) components: precipitation, evaporation, and runoff from 1950 to 2022 for lakes Superior, Michigan-Huron, Erie, and Ontario. A black line is plotted to help represent the patterns and trends in the data on a monthly and annual temporal scale. These trends are based on the data shown from 1950 to 2022 and may not be reflective of future trends.

Each lake has a graph showing monthly and annual average surface water temperatures, and a graphic showing monthly and annual maximum ice cover. Below the graphs are tables describing past conditions, Average surface water temperatures are shown over the period 1995-2022 and ice cover is shown from November 1972 to June of 2023. Note that the years on the annual plots refer to "Ice Years", which starts in November or December of the previous year. For example, the ice year of 2015, would be from November 2014 to June 2015.

Net Basin Supply Conditions   Net Basin Supply Conditions
 

 

Net Basin Supply Conditions   Net Basin Supply Conditions
 

 

 
Basin Parameter
Monthly Trend Observations
Annual Trend Observations
Precipitation
July and October saw a drop in precipitation in 2022. 
Since the 1970s, high annual rates of precipitation have been more frequent.
Evaporation
Evaporation in May, June. July, and August, shows a slight increasing trend in the last two to three decades.
Annual rates of evaporation in the last two decades have been generally higher and show a slight increasing trend.
Runoff
Lower runoff rates were experienced in January and October 2022 than in recent years.
After a few years with high runoff, recent years have had lower runoff rates. 
Surface Water Temperatures
Surface water temperatures in the summer and fall months experienced a large decrease from 2021 to 2022.
Surface water temperatures in 2022 were lower than they were in recent years. 
Ice Cover
Ice cover in February and March was much lower in 2023 than in the previous year. 

Ice cover in winter 2023 was under 25%, which was much lower than the previous winters of 2022 and 2021.  
Net Basin Supply Conditions   Net Basin Supply Conditions
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Net Basin Supply Conditions   Net Basin Supply Conditions
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Basin Parameter
Monthly Trend Observations
Annual Trend Observations
Combined Lakes Michigan-Huron Precipitation
February to May 2022 had higher precipitation than in 2021. 
In 2022, annual precipitation was below the higher rates of the preceding 5 years.
Combined Lakes Michigan-Huron Evaporation
Evaporation during July and August has shown an increasing trend in the last 3 decades. January 2022 experienced a major increase in evaporation.
Annual accumulated evaporation has shown an increasing trend over the last 4 decades.
Combined Lakes Michigan-Huron Runoff
Runoff increased in the Spring and stayed relatively consistent otherwise. 
Over the last two decades, annual runoff rates show an increasing trend, but the past two years have been lower.
Lake Michigan Surface Water Temperatures
Surface water temperatures underwent a large decrease from 2021 to 2022 in June and October. 
Surface water temperatures in September 2022 were high, similar to 2021.
Lake Huron Surface Water Temperatures
September was the only month that had a higher surface water temperature in 2022 than in 2021.

Annual surface water temperatures have remained relatively consistent over the past two decades.
Lake Michigan Ice Cover
Over the past winter, ice cover was higher in December but lower in all other months.

The most recent years with significant ice cover were during the winters of 2013-2014 and 2014-2015.
Lake Huron Ice Cover
Ice cover in January, February, and March were much lower in 2023 than in 2022.
There is substantial variability in ice cover throughout the period of record (1972-present).
Net Basin Supply Conditions   Net Basin Supply Conditions
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Net Basin Supply Conditions   Net Basin Supply Conditions
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Basin Parameter
Monthly Trend Observations
Annual Trend Observations
Precipitation
October had a significant decrease in precipitation in 2022. 
Precipitation in 2022 was lower than the past 5 years
Evaporation
Evaporation rates during September show a decreasing trend in the last two decades, despite higher rates in recent years.
Evaporation does not show signs of any trend on the annual timescale since 1950.
Runoff
Runoff during December and January has been lower in recent years and indicates a slight decreasing trend. 
After several years of high runoff, rates have been lower in the past few years. 
Surface Water Temperatures
Surface water temperatures in October 2022 were much lower than in 2021.
Surface water temperatures in November have been higher in recent years.
Ice Cover
Lake Erie is the shallowest Great Lake, and therefore usually experiences higher ice cover from year to year.

Ice cover on Lake Erie was much lower in 2023 than in the previous two years.
Net Basin Supply Conditions   Net Basin Supply Conditions
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Net Basin Supply Conditions   Net Basin Supply Conditions
Download .PDF   Download .PDF

 

 
Basin Parameter
Monthly Trend Observations
Annual Trend Observations
Precipitation
July and October saw a drop in precipitation in 2022.
Since the 1970s, high annual rates of precipitation have been more frequent.
Evaporation
Evaporation in May, June. July, and August, shows a slight increasing trend in the last two to three decades.
 Annual rates of evaporation in the last two decades have been generally higher and show a slight increasing trend.
Runoff
Lower runoff rates were experienced in January and October 2022 than in recent years. 
After a few years with high runoff, recent years have had lower runoff rates. 
Surface Water Temperatures
Surface water temperatures in November have been higher in recent years.
Annual surface water temperatures have been relatively consistent over the past three years on Lake Ontario.
Ice Cover
As a result of Lake Ontario's depth and location, generally low ice cover is seen from year to year.

Ice cover was much lower in 2023 compared to 2022.

 

Precipitation data is from the Great Lakes Seasonal Hydrological Forecasting System.

Evaporation data is modeled using the Large Lake Thermodynamics Model (LLTM).

Croley, T. E. (1989). Verifiable evaporation modeling on the Laurentian Great Lakes. Water Resources Research, 25(5), 781-792.

Runoff data is modeled using the Large Basin Runoff Model (LBRM).

Croley, T. E. (2002). Large basin runoff model. Mathematical models in watershed hydrology, 717-770.

Lofgren, B. M., & Rouhana, J. (2016). Physically Plausible Methods for Projecting Changes in Great Lakes Water Levels under Climate Change Scenarios. Journal of Hydrometeorology, 17(8), 2209-2223.

Surface water temperature data is provided at a daily time step with a period of record is from October 1994 to present from http://coastwatch.glerl.noaa.gov/statistic/.

Ice cover data is also provided on a daily time step and can be found at https://www.glerl.noaa.gov/data/ice/#historical (daily averages by lake). The period of record is from November 1972 to June 2023. Please note that years on the annual plots refer to "Ice Years", which starts in November or December of the previous year. For example, the ice year of 2015, would be from November 2014 to June 2015.

Graphics inspired by Hunter et al. 2015.

Hunter, T. S., Clites, A. H., Campbell, K. B., & Gronewold, A. D. (2015). Development and application of a North American Great Lakes hydrometeorological database—Part I: Precipitation, evaporation, runoff, and air temperature. Journal of Great Lakes Research, 41(1), 65-77.

Trend lines shown in black on the NBS graphics are calculated using a locally weighted regression based on http://www.rdocumentation.org/packages/stats/versions/3.5.1/topics/loess. 

 

Explore Great Lakes Water Management

This page contains monthly mean lakewide water levels (from 1918 to present) including long-term averages, maximums minimums, and monthly means. It also includes daily Great Lakes water levels and real-time gage data for connecting channels water levels. Water Level Data
Water Level Data
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Forecasts Forecasts
Forecasts
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Stop log (bulk heads) openings allow the lock to be re-filled with water after winter maintenance is complete. Outflows & Regulation
Outflows & Regulation
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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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