Vol. 187 Great Lakes Update August 2012 

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Great Lakes Winter and Spring Summary 

January – June 2012

The US Army Corps of Engineers (USACE) 

Detroit District monitors hydraulic and 

hydrologic conditions of the Great Lakes. This 

update article provides a summary of the Great 

Lakes water levels and basin conditions for 

January 2012 through June 2012. The report will 

also address some of the most recent frequently 

asked questions to our Hydraulics and Hydrology 

Office. 

All of the Great Lakes are currently below their 

long-term average (LTA) water levels due to the 

recent dry conditions around the basin. With the 

exception of Lake Superior, all of the Great Lakes 

are also below their levels of one year ago. More 

detailed information for each lake’s water level 

follows below. 

All water levels mentioned in this article are 

monthly mean surface elevations in feet on the 

International Great Lakes Datum of 1985 (IGLD 

85). All values shall be considered preliminary 

until final levels are coordinated between U.S. 

and Canadian agencies, sometime in early 2013. 

The official period of record for Great Lakes 

water levels is 1918 – 2011. Official water level 

statistics and historical water levels are located on 

the internet at the following address. 

http://www.lre.usace.army.mil/greatlakes/hh/grea

tlakeswaterlevels/historicdata/

Lake Superior 

Lake Superior’s water level is currently 2 inches 

higher than one year ago but 9 inches below its 

LTA as of the end of June. As shown in Figure 1, 

the water level has followed the typical pattern of 

falling through the winter months until March and 

has risen steadily since then. From December 

2011, the water level has risen 4 inches in 2012, 

compared to a typical rise of 2 inches. 

Figure 1: 2012 Lake Superior Water Levels 

The greater than average water level rise for Lake 

Superior in 2012 has been caused by wetter than 

average basin conditions, especially for May and 

June. Figure 2 shows the monthly totals of 

precipitation for the Lake Superior basin. Lake 

Superior has received a total of 15.2 inches of 

Great Lakes

Update 
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over-basin precipitation in 2012, compared to a 

historical average of 13.2 inches. 

Portions of the Lake Superior basin were 

inundated by very heavy rain during the month of 

June. In a period of just over 3 days, locations in 

and around Duluth, MN received in excess of 10 

inches of rainfall. This rain caused significant 

flooding and extremely high flows in the St. 

Louis River, which feeds Lake Superior. The 

combination of the heavy rain and increased 

runoff caused Lake Superior to rise 4 inches from 

June 18th to the 21st. 

Figure 2: Lake Superior 2012 Monthly Precipitation 

Another factor which has contributed to Lake 

Superior’s greater than average water level rise is 

the below average outflow through the St. Marys 

River. The regulated flow, internationally 

coordinated by the Lake Superior Board of 

Control according to Regulation Plan 1977-A, has 

been below average as shown in Figure 3. 

The water level of Lake Superior will continue its 

seasonal rise until September and then begin its 

seasonal decline. The lake is forecasted to stay 1 

to 4 inches above last year’s level over the 

remainder of 2012 and is expected to stay around 

9 inches below the LTA. 

Figure 3: Lake Superior 2012 Outflow through the St. 

Marys River 

Lake Michigan-Huron 

Lake Michigan and Lake Huron are treated as one 

lake because they maintain the same water level 

due to the hydraulic connection at the Straits of 

Mackinac. June’s monthly mean water level for 

Lake Michigan-Huron was 19 inches below the 

long-term average and 6 inches below the level of 

one year ago. The Lake Michigan-Huron water 

levels of 2012 are shown in Figure 4. Typically, 

the lake level rises 9 inches from December’s 

monthly mean water level to June’s mean level, 

but in 2012 the water level has only risen 1 inch 

from December 2011. 

Figure 4: 2012 Lake Michigan-Huron Water Levels 
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The below average rise of the water level has 

been caused by dryer than average basin 

conditions so far in 2012. Figure 5 shows the 

monthly precipitation totals for Lake MichiganHuron. The basin typically receives 14.8 inches 

of precipitation during the first six months of the 

year, but has only received 12.4 inches in 2012. 

Figure 5: Lake Michigan-Huron 2012 Monthly 

Precipitation 

The water level of Lake Michigan-Huron is also 

influenced by the inflow through the St. Marys 

River (see Figure 3) and the outflow through the 

St. Clair River. Figure 6 shows that the outflow 

from Lake Huron through the St. Clair River has 

been below average in 2012, with the exception 

of February where the outflow was slightly above 

average. Therefore, the recent lower water levels 

on Lake Michigan-Huron are primarily due to dry 

basin conditions. 

Low water levels are expected to continue for 

Lake Michigan-Huron through the remainder of 

2012. As is typical, the levels are forecasted to 

continue a seasonal decline over the next six 

months. The latest forecast shows the lake 

remaining 21 to 22 inches below the LTA and 7 

to 10 inches below 2011 levels. 

Figure 6: Lake Michigan-Huron Outflow through the 

St. Clair River 

Lake St. Clair 

The water level of Lake St. Clair is currently 9 

inches below the level of one year ago and 7 

inches below the LTA. Figure 7 shows the Lake 

St. Clair water levels thus far in 2012 compared 

to average. The lake usually rises 10 inches from 

December to June, but the June 2012 mean level 

is actually 4 inches below December 2011’s mean 

level. 

Figure 7: 2012 Lake St. Clair Water Levels 

Similar to the Michigan-Huron basin, the St. Clair 

basin has been experiencing dryer than average 

conditions. Figure 8 shows the 2012 precipitation 
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for the Lake St. Clair basin compared to average. 

Historically, Lake St. Clair has received an 

average of 16 inches of precipitation from 

January through June, but the 2012 total 

precipitation is 14 inches. 

Figure 8: Lake St. Clair 2012 Monthly Precipitation 

The level of Lake St. Clair is also affected by the 

outflow from the lake through the Detroit River. 

The 2012 monthly average flows through the 

Detroit River are shown in Figure 9. With the 

exception of February, the monthly mean flows 

through the Detroit River have been below 

average. Therefore, the recent lower water levels 

are caused by the basin’s dry weather. 

Figure 9: Lake St. Clair Outflow through the Detroit 

River

Lake St. Clair is also expected to follow the 

typical seasonal decline for the remainder of 

2012. From July’s mean water level to 

December, the lake is predicted to fall 13 inches. 

The water levels are forecasted to stay 12 to 13 

inches below the LTA through December and 13 

to 19 inches below last year. 

Lake Erie 

Lake Erie’s water level is currently 14 inches 

below the level of one year ago and 4 inches 

below the LTA. As shown in Figure 10, the 

water level of Lake Erie has not followed the 

usual pattern over the last 7 months. Typically, 

Lake Erie rises 13 inches over the first half of the 

year, but the level has dropped 7 inches over the 

first half of 2012. 

Figure 10: 2012 Lake Erie Water Levels

A large deficit of precipitation has been occurring 

in the Lake Erie basin in recent months. As seen 

in Figure 11, May precipitation was less than half 

of the historical average, with April and June also 

being very dry months. Usually Lake Erie 

receives 10 inches of precipitation during April, 

May, and June, but in 2012 it has only received 5 

inches during those three months. 
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Figure 11: Lake Erie 2012 Monthly Precipitation 

Similar to the unusual water level decline for 

Lake Erie, there has also been a drop in the Lake 

Erie outflow. As shown in Figure 12, the Lake 

Erie outflow was above average in early 2012, 

but since then the flow has fallen below average. 

The combination of above average outflow in 

early 2012 with very dry basin conditions in 

recent months have caused Lake Erie’s water 

level to decline. 

Figure 12: Lake Erie Outflow

The latest six month forecast shows Lake Erie’s 

water level falling 15 inches from July to 

December, when typically the lake falls 13 

inches. By December, the water level of Lake 

Erie is forecasted to be 25 inches below its 

December 2011 level. Although the lake has 

dropped a large amount from 2011 levels, it is 

expected to remain 8 to 9 inches below the LTA 

for the rest of the year. 

Lake Ontario 

The water level of Lake Ontario is 17 inches 

below the level of one year ago and 6 inches 

below the LTA. Lake Ontario started 2012 above 

the LTA, as seen in Figure 13. From December’s 

monthly mean level to February, Lake Ontario 

rose 15 inches. Since then it has dropped 4 

inches. Typically, Lake Ontario rises 20 inches 

from December to June, but from December 2011 

it has only risen 11 inches in 2012. 

Figure 13: 2012 Lake Ontario Water Levels

Lake Ontario has also experienced a dry year, 

especially during the February through May 

period. Figure 14 shows that the precipitation 

totals during these months were well below 

average. Typically, the January through June 

total precipitation for Lake Ontario is 17 inches. 

In 2012, the total precipitation has been only 13 

inches. The huge lack of precipitation caused a 
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direct impact to the water level of Lake Ontario, 

as can be seen by comparing Figures 13 and 14. 

Figure 14: Lake Ontario 2012 Monthly Precipitation 

Outflow through the St. Lawrence River is 

regulated by the International St. Lawrence River 

Board of Control. As seen in Figure 15, the 

outflow from Lake Ontario through the St. 

Lawrence River during the first four months of 

2012 was above average and has been below 

average since then. 

Figure 15: Lake Ontario Outflow through the St. 

Lawrence River

Lake Ontario typically falls 18 inches from July 

to December, but is only expected to fall 15 

inches during the same time frame this year. This 

would move Lake Ontario from 8 inches below to 

4 inches below the LTA. The level of the lake is 

expected to remain 6 to 14 inches below 2011 

levels. 

FREQUENTLY ASKED QUESTION:

How will the warm air temperatures affect the 

lake levels? 

Sustained warm air temperatures increase the 

water temperatures of the Great Lakes, especially 

at the water surface. Currently, the surface 

temperatures of each of the Great Lakes are 

above average for this time of year. Figures 16 

through 20 below are from the Great Lakes 

Coastwatch website provided by NOAA 

(http://coastwatch.glerl.noaa.gov/) and compare 

the surface water temperatures of 2012 to the 

available period of record averages. 

Figure 16: Lake Superior Surface Temperatures 
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Figure 17: Lake Michigan Surface Temperatures 

Figure 18: Lake Huron Surface Temperatures 

Figure 19: Lake Erie Surface Temperatures 

Figure 20: Lake Ontario Surface Temperatures 

The very warm temperatures experienced this 

summer have been the result of persistent high 

pressure systems sitting over the eastern U.S. 

These high pressure systems allowed 

temperatures to soar into the 90s and 100s. 

Locations as far north as Marquette, Michigan 

recorded daytime high temperatures well into the 

90s this summer. 

The warmer than average water temperatures may 

lead to increased evaporation rates this fall and 

winter, when air temperatures are often colder 

than the water temperatures. 

FREQUENTLY ASKED QUESTION:

Why are the lake levels currently low? 

There are a variety of factors which cause the 

lake levels to fluctuate. Primarily, they are 

influenced by precipitation on the lake, runoff 

into the lake from precipitation falling on the 

lake’s watershed, and evaporation from the lake 

surface. 

The lack of snowfall this winter played a major 

role in reducing the amount of spring runoff to all 

of the Great Lakes. Table 1 below lists the 

estimated runoff totals, as a percent of average, 

for the first six months of 2012 according to the 
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Great Lakes Advanced Hydrologic Prediction 

System (AHPS) model developed by NOAA 

Great Lakes Environmental Research Laboratory. 

Table 1: Runoff Totals Jan. – June 2012 as % of 

Average (AHPS model) 

Superior Mich-Hur St. Clair Erie Ontario 

85% 71% 77% 60% 55% 

By looking at precipitation totals shown in Figure 

21 below, you will see that only Lake Superior 

has received above average precipitation in 2012. 

Lake Superior is also the only Great Lake with 

higher water levels than a year ago. This lack of 

precipitation on all of the other lake basins has 

been a major contributor to low lake levels. 

Figure 21: Total 2012 Precipitation Through June, 

Compared to Average 

FREQUENTLY ASKED QUESTION:

Has the Chicago diversion lowered the levels of 

the Great Lakes? 

The Chicago Diversion diverts water from Lake 

Michigan into the Mississippi River watershed. 

In 1967, the US Supreme Court decreed that a 

total of 3,200 cubic feet per second was allowed 

to flow through the Chicago Diversion. This flow 

is audited by the USACE Chicago District, the 

US Geologic Survey, the Illinois Department of 

Transportation, and the Metropolitan Water 

Reclamation District of Chicago. In comparison, 

the allowed flow through the diversion is 1.7% of 

the water flowing out of Lake Michigan-Huron 

through the St. Clair River. 

There is also a diversion of water into the Great 

Lakes through the Long Lac and Ogoki 

diversions. The amount of water diverted into 

Lake Superior averages 5,000 cubic feet per 

second, or almost 2,000 cubic feet per second 

greater than the amount of water allowed out 

through the Chicago Diversion. The net total of 

the inter-basin diversions in the Great Lakes 

shows more water diverted into the lakes than 

out. 

More Information 

In addition to the Monthly Bulletin, the Detroit 

District issues the Weekly Great Lakes Water 

Level Update and the Weekly Great Lakes 

Connecting Channels Water Levels and Depths. 

Both products are updated each Thursday and can 

be located here: 

http://www.lre.usace.army.mil/greatlakes/hh/grea

tlakeswaterlevels/waterlevelforecasts/

The Detroit District welcomes comments on all of 

our 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