Volume 207: Great Lakes Information Website 101

Background 

This Update Article is an informational guide to 

the Great Lakes water level data and forecasts, as 

well as the data, graphs, and documents describing 

the basin conditions that influence Great Lakes 

water levels, that are available on the Detroit 

District’s website.

Great Lakes Information Webpage 

Great Lakes water level data and forecasts can be 

accessed from the “Great Lakes Information” 

Section of the Detroit District’s website. The web 

address to the Detroit District Home Page is:

https://www.lre.usace.army.mil/

To navigate to the “Great Lakes Information 

Section”, hover over the word, “Missions”, on the 

black Tool Bar at the top of the page, and click on 

“Great Lakes Information” 

Figure 1: USACE Detroit District Home Webpage. 

or go directly to the following web address: 

https://www.lre.usace.army.mil/Missions/GreatLakes-Information/

Once you have reached the “Great Lakes 

Information” page, click on “Expand All” 

underneath the “Great Lakes Information” 

heading. 

Figure 2: “Great Lakes Information” Main Page. 

There are 4 main sections of the Great Lakes 

Information” webpage – “Water Level Data”, 

“Water Level Forecasts”, “Great Lakes Basin 

Conditions”, and “Great Lakes Update 

Articles”. These sections can be accessed by 

clicking inside their respective boxes. 

Water Level Data Section

At the top of the “Great Lakes Water Level Data” 

page is the “Monthly mean lakewide average 

water levels” section. This section provides links 

to tables of coordinated monthly mean water level 

statistics for each lake encompassing the lakes’ 

entire period of record, 1918-2019 (Figure 4). You 

have the option to view the statistics in English or 

Metric Units. The water levels are referenced to 

Great Lakes

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Vol. 207 Great Lakes Update November 2020 

Page 2

the International Great Lakes Datum 1985. There 

are two additional links that provide monthly mean 

water levels for each lake for every year in their 

period of record in both English and Metric units. 

On the right side of the page is a graphic of the 

monthly mean levels of all the lakes plotted for 

their entire period of record and the current year’s 

preliminary monthly mean levels, which can be 

clicked on for a larger view.

Figure 3: “Great Lakes Water Level Data” Main 

Page and “Monthly mean lakewide average water 

levels” section. 

Figure 4: Snippet of Coordinated Monthly Great 

Lakes Water Level Statistics in the “Monthly mean 

lakewide average water levels” section (showing 

Lake Superior). 

Scrolling further down the “Great Lakes Water 

Level Data” page, under the heading, “Daily 

Lakewide Average Water Levels”, are links to 

the Great Lakes Water Levels Reports and a plot 

of daily levels for each lake for the current and 

previous year. This plot can be clicked on for a 

larger version of the plot in PDF format.

Figure 5: Top portion of “Daily Lakewide Average 

Water Levels” Section. 

The Great Lakes Water Levels Reports show daily 

levels and monthly mean levels for the current 

month for each lake. Great Lakes Water Level 

Reports for the prior 3 months are also provided. 

Web Address: 

https://www.lre.usace.army.mil/Missions/GreatLakes-Information/Great-Lakes-Information2/Water-Level-Data/

Figure 6: Great Lakes Water Levels Reports. 

The daily lake-wide average (LWA) water level of 

each lake shown on the water level reports are 
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Page 3

calculated by averaging the daily water levels at 

designated gauges around each lake. The gauges 

are operated and maintained by the National 

Oceanographic and Atmospheric Administration

(NOAA) and the Canadian Hydrographic Service

(CHS). Pages 2 through 6 of the Water Level 

Reports show the preliminary daily levels for each 

of the water level gauges used to calculate the 

LWA levels (Figure 7).

Figure 7: Lake Michigan-Huron page of the Water 

Level Reports showing the daily levels at each 

gauge used to calculate the Michigan-Huron LWA 

level.

These LWA water levels are provisional, as they 

are based on real-time gauge data. Real-time data 

is data that is delivered as soon as it is gathered, 

and is not final, verified data.

Lastly, concerning the connecting channels of the 

Great Lakes, tables of hourly water levels for the 

past 7 days, and daily water levels over the past 30 

days, for designated gauges along the St. Marys, 

St. Clair, and Detroit Rivers, are provided at the 

bottom of the “Great Lakes Water Level Data”

section. This provisional data comes from 

USACE gauges, as well as NOAA and CHS 

gauges.

Water Level Forecasts

Figure 8: “Water Level Forecasts” Main Page.

Web Address: 

https://www.lre.usace.army.mil/Missions/GreatLakes-Information/Great-Lakes-WaterLevels/Water-Level-Forecast/

The first featured Water Level forecast is the 

Weekly Forecast. It forecasts Great Lakes water 

levels 30 days out from the day it is published. It

is performed every Thursday, and posted to the 

website on Friday.

Figure 9: Weekly Water Level Forecast.
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The next featured forecast is the Connecting 

Channels Forecast. It accompanies the Weekly 

Water Level Forecast every Friday. This forecast 

predicts water depths, relative to low water datum, 

at designated locations in the St. Marys, St. Clair, 

Detroit, and St. Lawrence Rivers 1, 2, 3, and 4 

weeks into the future.

Figure 10: Top of Connecting Channels Forecast.

The next featured forecast is the Monthly Bulletin

of Great Lakes Water Levels.

Figure 11: Monthly Bulletin of the Great Lakes 

(showing Lake Michigan-Huron’s graphic

specifically).

This forecast is performed at the beginning of each 

month. It forecasts monthly mean water levels 6 

months out, and is coordinated with Environment 

and Climate Change Canada.

USACE also produces a 12-month Water Level 

Outlook (Figure 12). 

Figure 12: Most recent Water Level Outlook for 

Lake Erie.

Water Level Outlooks are not technically 

forecasts. They are projections of water levels over 

the next 12 months if the Net Basin Supply – the 

combined effects of precipitation falling directly 

onto the lake surface, runoff from the land draining 

into the lake, and evaporation from the lake surface 

- matches certain historical net basin supply

sequences of interest. The Outlook’s scenarios are 

updated every 3 months and the graphics are 

updated monthly.

Great Lakes Basin Conditions Section

The “Great Lakes Information” page also provides 

information on the hydrometeorological 

conditions that impact water level fluctuations in 

the “Great Lakes Basin Conditions” section. 

This section is divided into 4 parts, “Recent Great 

Lakes Basin Conditions”, “Recent Net Basin 

Supply Conditions, “Other Recent Great Lakes 

Basin Conditions”, and “Long Term Trends in 

Great Lakes Basin”.

The “Recent Great Lakes Basin Conditions”

section contains links to the Monthly Hydrology 

Summaries and Monthly Water Level Summaries 

that are prepared in tandem with the Monthly 
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Great Lakes Water Level Bulletin. Links to the 

latest 12 months of each of these summaries are 

provided; just click on the month/date to open the 

document.

Figure 13: Top of “Recent Great Lakes Basin 

Conditions” Home Page.

The Monthly Hydrology Summaries highlight the 

previous month’s net basin supply, precipitation, 

outflows, and latest month-to-month water level 

change for each Great Lake (Figure 14). 

Figure 14: Monthly Basin Hydrology Summaries.

The Monthly Water Level Summaries provide 

details on last month’s water levels for each Great 

Lake and how they compare to the prior month’s 

mean level, its long-term average mean level, and 

its level of a year ago. In addition, they include 

observations on how water level changes relate to 

recent hydrological conditions, and summarize 

how the latest Monthly Bulletin predicts the water 

levels over the next 6 months will compare to 

long-term average levels and last year’s levels

(Figure 15).

Figure 15: August 2020 Water Level Summary for 

Lake Superior.

Just underneath “Recent Great Lakes Basin 

Conditions”, is the “Recent Net Basin Supply 

Conditions” section. Click on “Expand All” at the 

top. This page contains 5-year (2015-2020) plots 

of monthly Net Basin Supply (NBS) for each lake.

Figure 16: Showing how to open Net Basin Supply 

(NBS) and Component Plots.
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Figure 17: Monthly NBS plots for the past 5 years 

(Superior and Michigan-Huron are shown).

5-year plots are also available for the individual 

components that constitute NBS - precipitation, 

runoff, and evaporation. The Precipitation plot 

displays final, coordinated data for years 2015-

2017, while data for 2018-2020 are from the 

USACE Daily Precipitation Reports. Runoff and 

Evaporation are calculated from the Advanced 

Hydrologic Prediction System (AHPS) developed 

by NOAA’s Great Lakes Environmental and 

Research Laboratory (GLERL). All plots show 

monthly deviation from long-term average.

There are numerous precipitation data options 

available in this section.

Figure 18: Showing the options for precipitation 

data available in the “Recent Net Basin Supply 

Conditions” Section.

The top-most option shown is the Daily 

Precipitation Report showing daily and monthly 

total precipitation for all the Great Lakes for the 

current month in Metric and English Units (Figure 

19). The Daily Precipitation Report for the 

previous month is also available in this section.

Figure 19: Daily Precipitation Report.

Web Address:

http://lrewm.usace.army.mil/reports/GreatLakes/GLPThisMonth.pdf

Daily precipitation data is obtained from weather 

gauges operated and maintained by the National 

Weather Service and various Canadian entities. 

Similar to daily water level data, this data is 

preliminary, not final.

Below the links to the Daily Precipitation reports, 

are links to tables of coordinated Great Lakes 

monthly precipitation statistics showing the 

monthly average, monthly record-high and 

monthly record-low precipitation for the period of 

1900-2017 for each lake basin (Figure 19). These 

statistics are provided in English and Metric Units.

In addition, this section contains links to the 

Midwest Regional Climate Center’s observed 

precipitation maps, the National Weather 

Service’s observed precipitation and precipitation 

forecast maps.

The “Other Recent Great Lakes Basin 

Conditions” section is also a source of useful 
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information about the factors that influence water 

level changes. This section includes plots of daily 

Great Lakes Snow Water Equivalent (SWE), Ice 

Cover, and Lake Surface Water Temperature. The 

Surface Water Temperature plots show data for the 

past 365 days, while the SWE and Ice Cover plots 

show daily data from September to May, and 

November to May, respectively.

Figure 20: Showing how to access SWE & Ice 

Cover plots.

The Snow Water Equivalent plot contains 

preliminary data obtained from NOAA’s National 

Operational Hydrologic Remote Sensing Center 

(NOHRSC). The Ice Cover and Surface Water 

Temperatures plots feature data developed by 

NOAA GLERL.

Figure 21: Plot of daily Ice Cover available on the 

Website. 

The “Long Term Trends in Great Lakes Basin 

Conditions” section is divided into two parts. The 

top part, entitled “NBS Components

(Precipitation, Runoff, Evaporation)” displays

plots of monthly and annual precipitation, runoff, 

and evaporation for years 1950 to 2019 for each 

Great Lake. These plots capture monthly and 

annual trends in these NBS components.

Figure 22: Top of “Long Term Trends in Great 

Lakes Basin Conditions” Section.

Figure 23: How to access enlarged plots.

Underneath the above-mentioned plots are links to 

Great Lakes precipitation data sources and a list of 

published articlesthat explain the modelsthat were 

developed to estimate Great Lakes evaporation 

and runoff.

The 2nd part of the section covers historical trends 

in Great Lake Surface Water Temperatures and Ice 

Cover. It includes plots of monthly and annual 
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Average Lake Surface Water Temperatures for 

years 1995 to 2019, and of Maximum Ice Cover 

for the years 1973 to 2019, for each Great Lake.

Figure 24: Plot of Lake Superior Monthly 

Maximum Ice Cover for years 1973 to 2019.

Great Lakes Update Articles

Electronic and printable PDF versions of this 

Update article, and all previous 206 Update 

Articles, dating back to 1985, can be accessed in 

this section. You can also get to this section by 

clicking on “Great Lakes Update Articles” on the 

left-hand side of the “Great Lakes Information” 

page, under the “Quick Links” heading or by 

typing in the following URL:

https://www.lre.usace.army.mil/Missions/GreatLakes-Information/News-and-Information/GreatLakes-Update-Articles/

Lake Superior Regulation

The Lake Superior Regulation section features 

documents and updates pertaining to regulation of 

Lake Superior’s outflow through the St. Marys 

River. 

Figure 25: Accessing “Lake Superior Regulation” 

webpage.

This Section can be accessed by clicking on “Lake 

Superior Regulation” on the left-hand side of the 

“Great Lakes Information” page, under the “Quick 

Links” heading. 

Web Address:

https://www.lre.usace.army.mil/Missions/GreatLakes-Information/Great-LakesInformation.aspx#ICG_ETH_22304

Figure 26: “Lake Superior Regulation” Section.

This section provides the News Release, published 

at the beginning of each month, that announces the 

new month’s gate setting of the St. Marys 

Compensating Works and the projected St. Marys 

River flow for the month. Also provided in this 

section is the hourly St. Marys River flow schedule 

for the current month and the Lake Superior 

Infographic created by the International Lake 

Superior Board of Control. Lastly, 

announcements of changes to gate openings that 

have been implemented during the month are 

posted in this section.

The Detroit District welcomes comments on all of 

our data and forecast products. Please email 

questions and comments to 

hhpm@usace.army.mil. To contact the District by 

phone call toll free 1-888-694-8313 and select 

option 1. The Detroit District’s mailing address is:

Department of the Army

Detroit District Corps of Engineers

ATTN: CELRE-HH-W

477 Michigan Avenue

Detroit, MI 48226