WEEKLY GREAT LAKES WATER LEVEL UPDATE

May 18, 2012

WEATHER CONDITIONS

Other than a few scattered showers across the Great Lakes basin in the early part of the week, the region has been experiencing fairly dry conditions over the last few days. Temperatures have dropped a bit since Tuesday and are currently near seasonal averages. Expect temperatures to rise with mostly clear conditions over the next couple of days. Scattered showers and thunderstorms are likely to arrive early next week.

LAKE LEVEL CONDITIONS

Lake Superior is near last year's level and Lake Michigan-Huron is 2 inches lower than the level of a year ago. Lakes St. Clair, Erie, and Ontario are 9, 7, and 13 inches, respectively, lower than a year ago. Over the next month, Lakes Superior and Michigan-Huron are forecasted to rise 3 and 2 inches, respectively, from their current levels. The water levels of Lakes St. Clair and Erie are expected to fall 1 and 2 inches, respectively, while the level of Lake Ontario is expected to rise 1 inch over the next thirty days. 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 projected to be below average for the month of May. Lake Huron's outflow into the St. Clair River and the outflow from Lake St. Clair into the Detroit River are expected to be below average throughout the month of May. Lake Erie's outflow through the Niagara River is forecasted to be above average and the outflow of Lake Ontario into the St. Lawrence River is predicted to be below average in May.

ALERTS

The water level of Lake Superior is below chart datum and is forecasted to remain below chart datum through July. 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 May 18, 2012 (feet)

600.56

577.62

574.08

571.78

245.83

Chart Datum (feet)

601.10

577.50

572.30

569.20

243.30

Difference from chart datum (inches)

-6

+1

+21

+31

+30

Difference from average water level for Apr 18, 2012 (inches*)

+1

+1

0

-1

+1

Difference from average water level for May 18, 2011 (inches*)

0

-2

-9

-7

-13

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

-12

-17

-6

-1

-3

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

-27

-48

-33

-27

-31

Year of highest recorded monthly mean

1986

1986

1986

1986

1973

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

+11

+13

+22

+33

+32

Year of lowest recorded monthly mean

1926

1964

1934

1934

1935

Projected change in levels by Jun 18, 2012 (inches)

+3

+2

-1

-2

+1

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, 1918-2011

FORECASTED INFORMATION PROVIDED BY

RECORDED DATA (1918 – present)

FOR MORE INFORMATION VISIT

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