Basin Conditions

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Great Lakes Hydraulics and Hydrology

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Recent Great Lakes Basin Conditions

Latest Monthly Hydrology and Water Level Summaries

Monthly Hydrology Summaries include information on the month's net basin supply and precipitation. These summaries are also included in the publication of the Monthly Bulletin of Great Lakes Water Levels. Monthly Water Level Summaries provide details on the water levels for each Great Lake, and include observations on how water level changes relate to recent hydrological conditions.

Click on the individual graphics below to view a larger, printer-friendly image (pdf).

Last Month Hydrology Summary	Last Month Water Level Summary

Graph of Great Lakes daily lakewide average water levels for current and previous year

Recent Net Basin Supply Conditions

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Click to view recent net basin supply, evaporation, precipitation, and runoff 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, as shown in the graphic above. 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. Click on the graphic to the right to view the NBS relative to long term average NBS for the past 5 years.
Precipitation Daily precipitation for current and previous months in English units Daily precipitation for current and previous months in metric units Long term average, maximum, and minimum precipitation in english and metric units Binational daily precipitation grids Quantitative Precipitation Forecasts going out 7 days from the National Weather Service National Weather Service Enhanced Radar National Mosaic Click on the graphic to the right to view basin-wide precipitation, relative to long term average, for the past 5 years.
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 lakes' surface. Click on the graphic to the right to view simulated evaporation rates from the Large Lake Thermodynamic Model, relative to average, for the past 5 years.
Runoff Runoff to the Great Lakes is typically highest during the spring, when melting snow combines with liquid precipitation, leading to increased streamflow. Click here to visit the North American WaterWatch site showing real-time streamflow compared to historical streamflow for U.S. and Canadian gages. Click on the graphic to the right to view simulated runoff rates from the Large Basin Runoff Model, relative to average, for the past 5 years.

Other Recent Great Lakes Basin Conditions

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Click to view other hydrometeorological conditions in the Great Lakes, including snow water equivalent, ice cover, and surface water temperature.

Snow Water Equivalent

Click on the graphic to the right to view snow water equivalent data from NOAA's National Operational Hydrologic Remote Sensing Center (NOHRSC) aggregated to Great Lakes basins.

Click here to view gridded snow water equivalent from NOAA's National Operational Hydrologic Remote Sensing Center (NOHRSC).

Graph of historical and current lake basin snow water equivalent

Ice Cover

Click on the graphic to the right to view recent and historical ice cover compiled from data from NOAA's Great Lakes Environmental Research Laboratory (GLERL).

Click here to view historical, current, and forecasted ice conditions for the Great Lakes from NOAA's Great Lakes Environmental Research Laboratory.

Graph of historical and current ice cover

Surface Water Temperature

Click on the graphic to the right to view recent and historical surface water temperatures compiled from data provided by NOAA's Great Lakes Environmental Research Laboratory (GLERL).

Click here to get recent and historical surface water temperatures for the Great Lakes from NOAA's Great Lakes Environmental Research Laboratory.

Graph of historical and current surface water temperature

Long Term Trends in Great Lakes Basin Conditions

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NBS Components (Precipitation, Evaporation, Runoff)

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, as shown in the graphic to the right. 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.

Graphic showing Great Lakes water balance components.

This page shows trends in precipitation, evaporation, and runoff from 1950 to 2021 for Lakes Superior, Michigan-Huron, Erie, and Ontario. There are four sections, one for each lake, that provide a table summarizing monthly and annual trends, a monthly graphic that displays values of precipitation, evaporation, and runoff by month from 1950 to 2021, and an annual graphic that shows the accumulated precipitation, evaporation, and runoff in each year from 1950 to 2021. 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 2021 and may not be reflective of future trends. See the Data Description section for more information.

Use the links below to go directly to the graphs for each lake.

Lake Superior Lake Michigan-Huron Lake Erie Lake Ontario Data Information

Lake Superior

Precipitation	Evaporation	Runoff
Precipitation during October shows an increasing trend from 1950 through the recent period.	Evaporation during the winter months has shown an increasing trend since the 1950s, but has leveled off in recent years.	After several years of high runoff in May and October, runoff has been lower in 2020 and 2021.
After several years of higher annual precipitation, precipitation has been lower in the last two years.	On average, annual accumulated evaporation has been increasing over the last 7 decades.	After a period of higher annual runoff rates, runoff has been lower in the last two years.

Lake Michigan-Huron

Precipitation	Evaporation	Runoff
In recent years, there have been more Aprils and Octobers with higher precipitation.	Evaporation during July and August has shown an increasing trend in the last 3 decades.	Runoff in May has shown an increasing trend over the last two decades. In recent years, higher runoff has also occurred during winter months with greater frequency.
In 2021, annual precipitation was below the higher rates of the preceding 5 years.	Annual accumulated evaporation has shown an increasing trend over the last 4 decades.	Over the last two decades, annual runoff rates show an increasing trend.

Lake Erie

Precipitation	Evaporation	Runoff
May and June precipitation show an increasing trend since 1950. Also, October precipitation shows an increasing trend over the last three decades.	Evaporation rates during September show a decreasing trend in the last two decades, despite higher rates in recent years.	Runoff during April and May have been higher in recent years and indicate a slight increasing trend.
The last two decades have generally brought slightly higher annual precipitation.	Evaporation does not show signs of any trend on the annual timescale since 1950.	After several years of high runoff, rates were lower in 2020 and 2021.

Lake Ontario

Precipitation	Evaporation	Runoff
June and October precipitation have seen higher precipitation totals in the last two to three decades, while September and November precipitation have a decreasing trend.	Evaporation during the summer months (June. July, & August), has an increasing trend in the last two to three decades.	Runoff during January shows an increasing trend over the last five decades. May and June runoff rates have also been higher in recent years.
Since the 1970s, high annual rates of precipitation have been more frequent.	Annual rates of evaporation in the last two decades have been generally higher and show a slight increasing trend.	After a few years with low runoff, recent years have had higher runoff rates, but generally there is no clear trend.

Data Information

NBS Component Data

Precipitation data is coming 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.

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.

**The black lines in the graphics are calculated using a locally weighted regression, more information located here: https://www.rdocumentation.org/packages/stats/versions/3.5.1/topics/loess

All NBS graphics will be updated in the spring of each year.

Surface Water Temperatures and Ice Cover

This page shows historical surface water temperatures and ice cover for Lakes Superior, Michigan, Huron, Erie, and Ontario. There are 5 sections, one for each lake, that provide a table describing past conditions, a graphic showing monthly and annual average surface water temperatures, and a graphic showing monthly and annual maximum ice cover. Average surface water temperatures are shown over the period 1995-2021 and ice cover is shown from November 1972 to June of 2022. Please 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.

Use the links below to go directly to the graphs for each lake.

Lake Superior Lake Michigan Lake Huron Lake Erie Lake Ontario Data Information

Lake Superior

Graph of monthly and annual maximum ice cover.

Surface Water Temperatures	Ice Cover
Surface water temperatures in August and September 2021 were warmer than the preceding 4 years, approaching the very warm temperatures recorded in 2016.	In the last 20 years, there has been more variability in ice cover (most notably in February, March, and April).
The largest variability in surface water temperatures occurs in July on Lake Superior.	Ice cover in winter 2022 was relatively high (>75%), exceeding the lower ice cover of 2020 and 2021.

Lake Michigan

Surface Water Temperatures	Ice Cover
Surface water temperatures in September to November 2021 were warmer than during the preceding 4 years. Surface water temperatures in October were warmer than in the last 25 years.	Ice cover in 2022 exceeded that of 2020 and 2021 but was still below the relatively high ice cover (>50%) of 2019.
The surface water temperatures were lower in July 2021 than in July 2020. However, surface water temperatures were higher than 2020 in June and August.	The most recent years with significant ice cover were during the winters of 2013-2014 and 2014-2015.

Lake Huron

Surface Water Temperatures	Ice Cover
The surface water temperatures were lower in July 2021 than in July 2020. However, surface water temperatures were higher than 2020 in June and August.	There is substantial variability in ice cover throughout the period of record (1972-present).
After relatively warm surface waters in October 2016 and 2017, the last three years have been cooler.	Ice cover in 2022 was greater than 50%, exceeding the lower ice cover of 2020 and 2021, but still below the relatively high ice cover of 2018 and 2019.

Lake Erie

Graph of annual Erie monthly and annual maximum ice cover.

Surface Water Temperatures	Ice Cover
Surface water temperatures in the summer months have been warmer in recent years.	Lake Erie is the shallowest Great Lake, and therefore usually experiences higher ice cover from year to year.
Surface water temperatures in October and November 2021 exceeded those of the last three years.	In 2022, ice cover on Lake Erie exceeded 90%, which was higher than the previous two years.

Lake Ontario

Graph of annual Ontario monthly and annual maximum ice cover.

Surface Water Temperatures	Ice Cover
The surface water temperatures during June and July of 2021 were lower than in 2020, while temperatures in August 2021 were slightly higher than 2020.	As a result of Lake Ontario's depth and location, generally low ice cover is seen from year to year.
The largest variability in surface water temperatures occurs in the late spring and early summer (May, June, & July).	Ice cover in 2022 exceeded 25% and was higher than the previous two winters.

Data Information

Surface Water Temperatures and Ice Cover Data

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

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 2022. 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.

Surface water temperature and ice cover graphics will be updated in the spring of each year.

Document Information and Assistance

NOTICE: Not all documents accessible via this page are readable using optical character recognition (OCR). For more information and/or assistance please call 313-226-6441.

Detroit District Disclaimer

NOTICE: All 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 Ave., 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.