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Weekly Forecast

ARMY CORPS OF ENGINEERS WEEKLY GREAT LAKES WATER LEVEL UPDATE

Jul 23, 2021

 

WEATHER CONDITIONS

Precipitation over the last week continued the recent trend in July with a few heavier bands of precipitation crossing each subbasin except Lake Superior. Lake Superior is now well below its month to date average rainfall while the other lakes are ahead of their month to date averages. The heavier bands of rain were due to the passage of frontal systems that also brought temperature swings across the region. Late last week saw a dip in temperatures before a warming trend occurred early this week. A second system late this week brought daily highs below average for much of the basin. Above average temperatures and rainfall are expected this weekend with forecasted rainfall patterns showing a reversal of the recent trend. The northern portion of the basin along a line from Duluth, MN to Port Huron, MI is expected to receive 0.5 to 1.25 inches of rain by Monday with lighter amounts to the south and east.

LAKE LEVEL CONDITIONS

Over the last month Lake Superior’s water level declined an inch while the other Great Lakes rose between 3 and 7 inches. All the Lakes remain below their 2020 levels. Lake Superior is only an inch from its long term average July level, while Lakes Michigan-Huron, St. Clair, and Erie remain high with levels of 16, 22 and 21 inches above their respective July long term average levels. Lake Ontario remains below its long term July average level, and is currently 8 inches below average. The water level forecast for August 23rd indicates that Lake Superior should remain near the same level while Michigan-Huron, St. Clair and Erie decline 1, 5, and 5 inches respectively. Lake Ontario is expected to rise a total of 2 inches during the forecast period. See our Daily Levels web page for more water level information.

FORECASTED MONTHLY OUTFLOWS/CHANNEL CONDITIONS

Lake Superior’s outflow through the St. Marys River is predicted to be average this July. Lake Michigan-Huron’s outflow through the St. Clair River and Lake St. Clair’s outflow into the Detroit River are forecasted to be above average for July. Lake Erie’s outflow into the Niagara River is predicted to be above average for July and Lake Ontario’s outflow through the St. Lawrence River is projected to be above average in July.

ALERTS

Water levels shown are still-water surface elevations over the entire lake surface. Water levels at specific locations may differ substantially due to meteorological influences. Official records are based on monthly average water levels and not daily water levels. Users of the Great Lakes, connecting channels and St. Lawrence River should keep informed of current conditions before undertaking any activities that could be affected by changing water levels. Mariners should utilize navigation charts and refer to current water level readings.

SUPERIOR

MICH-HURON

ST. CLAIR

ERIE

ONTARIO

Forecasted Water Level for Jul 23, 2021 (feet)

602.20

580.74

576.74

573.75

245.41

Chart Datum (feet)

601.10

577.50

572.30

569.20

243.30

Difference from chart datum (inches)

+13

+39

+53

+55

+25

Difference from average water level for Jun 23, 2021 (inches*)

-1

+4

+7

+6

+3

Difference from average water level for Jul 23, 2020 (inches*)

-10

-18

-9

-6

-14

Difference from long-term monthly average of Jul (inches)

+1

+16

+22

+21

-8

Difference from highest monthly average of record for Jul (inches)

-12

-18

-10

-10

-39

Year of highest recorded monthly mean

2019

2020

2019

2019

2019

Difference from lowest monthly average of record for Jul (inches)

+23

+48

+51

+56

+26

Year of lowest recorded monthly mean

1926

1964

1934

1934

1934

Projected net change in levels by Aug 23, 2021 (inches)

0

-1

-5

-5

+2

ALL DATA SHOWN IN THIS SUMMARY ARE REFERENCED TO IGLD 1985

*VALUES FOR SPECIFIC DAY ARE BASED ON 3-DAY DAILY AVERAGE AROUND SPECIFIED DATE

LONG TERM AVERAGE PERIOD OF RECORD, 1918-2020

FORECASTED INFORMATION PROVIDED BY

RECORDED DATA (1918 – present)

FOR MORE INFORMATION VISIT

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Weekly Great Lakes Water Levels

We do not have the ability to offer email updates at this time.  The Weekly Forecast of Great Lakes Water Levels is updated each week on Thursday afternoon or Friday morning depending on data availability.

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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.