Basin Conditions

/ / /

Great Lakes Hydraulics and Hydrology

Quick Links

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

Collapse All Expand All

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

Collapse All Expand All

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

Collapse All Expand All

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 2022 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 2022, and an annual graphic that shows the accumulated precipitation, evaporation, and runoff in each year from 1950 to 2022. 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. 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 April shows an increasing trend since the 1980s through the recent period and was noticeably high in April 2022.	Evaporation during the winter months has shown an increasing trend since the 1950s, and was particularly high in January of 2022.	Runoff in May 2022 was very high, contributing to the overall increasing trend seen over the last two decades.
After two years of lower annual precipitation, 2022 was higher.	On average, annual accumulated evaporation has been increasing over the last 7 decades.	2022 runoff rates were higher than the previous two years.

Lake Michigan-Huron

Precipitation	Evaporation	Runoff
February to May 2022 had higher precipitation than in 2021.	Evaporation during July and August has shown an increasing trend in the last 3 decades. January 2022 experienced a major increase in evaporation.	Runoff increased in the Spring and stayed relatively consistent otherwise.
In 2022, 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, but the past two years have been lower.

Lake Erie

Precipitation	Evaporation	Runoff
October had a significant decrease in precipitation in 2022.	Evaporation rates during September show a decreasing trend in the last two decades, despite higher rates in recent years.	Runoff during December and January has been lower in recent years and indicates a slight decreasing trend.
Precipitation in 2022 was lower than the past 5 years.	Evaporation does not show signs of any trend on the annual timescale since 1950.	After several years of high runoff, rates have been lower in the past few years.

Lake Ontario

Precipitation	Evaporation	Runoff
July and October saw a drop in precipitation in 2022.	Evaporation in May, June. July, and August, shows a slight increasing trend in the last two to three decades.	Lower runoff rates were experienced in January and October 2022 than 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 high runoff, recent years have had lower runoff rates.

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 1995-2022 and ice cover is shown from November 1972 to June of 2023. 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 the summer and fall months experienced a large decrease from 2021 to 2022.	Ice cover in February and March was much lower in 2023 than in the previous year.
Surface water temperatures in 2022 were lower than they were in recent years.	Ice cover in winter 2023 was under 25%, which was much lower than the previous winters of 2022 and 2021.

Lake Michigan

Surface Water Temperatures	Ice Cover
Surface water temperatures underwent a large decrease from 2021 to 2022 in June and October.	Over the past winter, ice cover was higher in December but lower in all other months.
Surface water temperatures in September 2022 were high, similar to 2021.	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
September was the only month that had a higher surface water temperature in 2022 than in 2021.	Ice cover in January, February, and March were much lower in 2023 than in 2022.
Annual surface water temperatures have remained relatively consistent over the past two decades.	There is substantial variability in ice cover throughout the period of record (1972-present).

Lake Erie

Graph of annual Erie monthly and annual maximum ice cover.

Surface Water Temperatures	Ice Cover
Surface water temperatures in October 2022 were much lower than in 2021.	Lake Erie is the shallowest Great Lake, and therefore usually experiences higher ice cover from year to year.
Surface water temperatures in November have been higher in recent years.	Ice cover on Lake Erie was much lower in 2023 than in the previous two years.

Lake Ontario

Graph of annual Ontario monthly and annual maximum ice cover.

Surface Water Temperatures	Ice Cover
Surface water temperatures in November have been higher in recent years.	As a result of Lake Ontario's depth and location, generally low ice cover is seen from year to year.
Annual surface water temperatures have been relatively consistent over the past three years on Lake Ontario.	Ice cover was much lower in 2023 compared to 2022.

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 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.

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.