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.

Hydrology Summaries	Water Level Summaries
June 2021 May 2021 April 2021 March 2021 February 2021 January 2021 December 2020 November 2020 October 2020 September 2020 August 2020 July 2020	June 2021 May 2021 April 2021 March 2021 February 2021 January 2021 December 2020 November 2020 October 2020 September 2020 August 2020 July 2020

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 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 2019 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 2019, and an annual graphic that shows the accumulated precipitation, evaporation, and runoff in each year from 1950 to 2019. 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 2019 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 to the mid 2000s.	Evaporation during the winter months has shown an increasing trend since the 1950s, but has leveled off in recent years.	Despite a general decreasing trend in runoff in April and May, runoff during April and May of 2019 was higher than in recent years.
Precipitation does not show signs of any trend on the annual timescale since 1950.	Annual accumulated evaporation has been increasing over the last 7 decades.	Runoff in 2019 was the highest since 2001.

Lake Michigan-Huron

Precipitation	Evaporation	Runoff
In recent years, there have been more Octobers with higher precipitation, while in July precipitation has been lower in recent years.	Evaporation during July and August has shown an increasing trend in the last 3 decades.	Runoff in April has shown a decreasing trend since 1950.
Precipitation does not show signs of any trend on the annual timescale since 1950.	Annual accumulated evaporation has shown an increasing trend over the last 4 decades.	In the last 10 years, runoff rates have been lower, but generally there is no clear trend.

Lake Erie

Precipitation	Evaporation	Runoff
May and June precipitation show an increasing trend since 1950, however May has been generally lower in recent years.	Evaporation has a decreasing trend in the last 2 decades during September and in the last decade during October.	Runoff shows a large amount of variability in the winter and early spring months, but no clear sign of a trend.
Precipitation does not show signs of any trend on the annual timescale since 1950.	Evaporation does not show signs of any trend on the annual timescale since 1950.	Runoff does not show signs of any trend on the annual timescale since 1950.

Lake Ontario

Precipitation	Evaporation	Runoff
June and October precipitation have an increasing trend since 1950, while September and November precipitation have a decreasing trend in the last 2 to 3 decades.	Monthly evaporation shows no clear trend in any month.	Runoff during March shows a decreasing trend in the last 20 years, while in May there has been an increasing trend.
Since the 1970s, high annual rates of precipitation have been more frequent.	Evaporation does not show signs of any trend on the annual timescale since 1950.	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 coordinated through 2016 and can be found on the Great Lakes Coordinating Committee website. Link: http://www.greatlakescc.org/wp36/home/coordinating-committee-products-and-datasets/ (not currently available)

Precipitation data for 2017 is from the USACE web reports. Link: https://www.lre.usace.army.mil/Missions/Great-Lakes-Information/Weather-Information/

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 1995-2019 and ice cover is shown from November 1972 to June of 2019. 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
After very warm surface water temperatures in 2016 during August and September, the last 3 years have been cooler.	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.	In 2019, Lake Superior experienced another year of high ice cover, similar to what occurred in the winters of 2013-2014 and 2014-2015.

Lake Michigan

Surface Water Temperatures	Ice Cover
The surface water temperatures in October and November from 2015-2017 were relatively warm, but have been cooler in recent years in 2018 and 2019.	The maximum ice cover on Lake Michigan is generally below 50% for most years. However, in 2018 and 2019 the maximum ice cover was slightly above 50%.
The surface water temperatures for the last 3 Junes (2016-2018) have been relatively warm, but in 2019 cooler temperatures were observed.	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 for the last 3 Junes (2016-2018) have been relatively warm, but in 2019 cooler temperatures were observed.	There is substantial variability in ice cover throughout the period of record (1972-present).
After relatively warm surface waters in November between 2015 and 2017, the last two years (2018 and 2019) have been cooler.	In 2018 and 2019, the maximum ice cover was above 75% on Lake Huron. The last time Lake Huron experienced ice cover above 75% was during the cold winters of 2013-2014 and 2014-2015.

Lake Erie

Graph of annual Erie monthly and annual maximum ice cover.

Surface Water Temperatures	Ice Cover
The surface water temperatures for the last 3 Junes (2016-2018) have been relatively warm, but in 2019 cooler temperatures were observed.	Lake Erie is the shallowest Great Lake, and therefore usually experiences higher ice cover from year to year.
After relatively warm surface waters in November between 2015 and 2017, the last two years (2018 and 2019) have been cooler.	During the last two winters of 2018 and 2019, the maximum ice cover was above 90%. The last time this occurred was in the winters of 2013-14 and 2014-15.

Lake Ontario

Graph of annual Ontario monthly and annual maximum ice cover.

Surface Water Temperatures	Ice Cover
The surface water temperatures for the last 3 Junes (2016-2018) have been relatively warm, but in 2019 cooler temperatures were observed.	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, and July).	In 2019, the maximum ice cover was 39.8%. The most recent year with high ice cover was 2015 when it reached 82%.

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 2018. 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 Technical Services, Great Lakes Hydraulics and Hydrology Office, 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.