Minor Seiche on Lake Michigan Wednesday Morning

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE CHICAGO IL
155 PM CDT WED AUG 22 2007

...MINOR SEICHE AFFECTS SOUTHERN LAKE MICHIGAN...

A MINOR SEICHE WAS OBSERVED ON SOUTHERN LAKE MICHIGAN THIS
MORNING. A SEICHE CAN BEST BE EXPLAINED AS A LARGE SLOSH ON A
LAKE...WHERE WATER FROM ONE SIDE OF THE LAKE IS FORCED OR PUSHED
TO THE OTHER SIDE OF THE LAKE THEN RETURNS TO THE OTHER SIDE OF
THE LAKE RESULTING IN A RISE IN THE WATER LEVELS. THIS OSCILLATION
OF LAKE WATER LEVELS WILL OFTEN CONTINUE WITH PEAKS AND LOWS IN
WATER LEVELS FOR SOME TIME BEFORE THE LAKE STABILIZES AGAIN.

MOST COMMONLY SEICHES ON LAKE MICHIGAN OCCUR AS A RESULT OF A
FAST MOVING LINE OF HIGH WIND PRODUCING THUNDERSTORMS...AND THIS
WAS THE CASE THIS MORNING. AS THE LINE OF THUNDERSTORMS RACED
ACROSS SOUTHERN LAKE MICHIGAN THIS MORNING PRODUCING WINDS OF 40
TO 60 MPH IT CAUSED WATER TO PILE UP ON THE EAST SIDE OF THE
LAKE...FOLLOWED BY THE SLOSH BACK TO THE WESTERN SHORES OF LAKE
MICHIGAN.

LAKE WATER LEVEL DATA OBTAINED FROM CALUMET HARBOR THIS MORNING
INDICATE THAT THE AMPLITUDE OF THIS SEICHE WAS ABOUT A FOOT AND A
HALF...WITH LAKE LEVELS PEAKING ABOUT SLIGHTLY LESS THAN A FOOT
ABOVE NORMAL AND FALLING TO LESS JUST UNDER A FOOT BELOW NORMAL.
HERE ARE THE OBSERVED MAXIMUM AND MINIMUM WATER LEVELS MEASURED SO
FAR THIS MORNING AT CALUMET HARBOR DURING THE SEICHE.

536 AM CDT          9.6 INCHES ABOVE NORMAL
730 AM CDT          9.0 INCHES BELOW NORMAL
930 AM CDT          7.3 INCHES ABOVE NORMAL
1136 AM CDT        5.7 INCHES BELOW NORMAL
142 PM CDT          3.8 INCHES ABOVE NORMAL

SOME VERY MINOR...LIKELY UNNOTICEABLE...FLUCTUATIONS IN LAKE LEVELS
WILL CONTINUE THIS AFTERNOON AS THE LAKE STABILIZES AGAIN IN THE
WAKE OF THIS MORNINGS SEICHE.

$$

IZZI



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