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Illinois, Kendall

Public Information Statement

Statement as of 7:58 PM CDT on July 28, 2014


... Near record cold mid lake water temperatures and waves heights
for Southern Lake Michigan early Monday morning...

The water temperature at the Southern Lake Michigan mid lake buoy
dropped to 14.9c (58.8f) for several hours this morning. Only
once before have water temperatures colder than that been
observed at the mid lake buoy this late in the Summer (july 28th
through August 31st)... which was back on August 29th/30th of 2009
when the water temperature dipped as low as 14.1c (57.4f).

Typically water temperatures at the southern mid lake buoy in late
July and August are in the upper 60s to mid 70s. A look back at
hourly observations from the southern mid lake buoy going back to
1981... prior to today there had only been 19 hourly observations
with water temperatures below 15.0c (59.0f) this late into the
Summer season. Out of over 25,000 observations that equates to
a frequency of less than one tenth of one percent!

Unusually large waves this morning actually contributed to the near
Cold Lake water temperatures. Large waves cause upwelling... which
brings colder sub-surface water upward toward the surface resulting
in a drop in surface water temperatures.

The text regarding the near record wave heights is from the public
information statement issued earlier this morning...

Multiple strong cold fronts moved across the region on Sunday
and brought an autumn-like pattern over Lake Michigan by Sunday
night into Monday morning. Gusty northerly winds behind the
second front were oriented along the fetch of the lake and
produced near record large waves for July at the Southern Lake
Michigan mid lake buoy. Wave heights at the hourly observations
peaked at 8.5 ft a little before 1 am early Monday morning.

Here are the top July wave heights by day at the south mid lake
buoy dating back to 1981:

     date highest wave observation
--------------------------------------------
1) July 21 1981 9.2 ft
2) July 15 1987 8.9 ft
3) July 28 2014 8.5 ft
   July 20 2007 8.5 ft
5) July 19 1996 8.1 ft
6) July 23 2013 7.9 ft

Prior to this morning... there had only been three other hourly
observations during the month of July with wave heights at or
above 8.5 ft at the south buoy. Looking at meteorological Summer
/June-August/... there had only been 56 hourly observations of wave
heights of 8.5 ft or higher prior to this morning. That is less
than 0.001 percent of all summertime observations at that buoy!

North winds like we saw Sunday night into Monday morning are
almost always the culprit to high waves over the lake. In all the
summertime instances of waves at or above 8.5 ft at the south
buoy... the wind direction was northwest... north... or northeast on
all but one of the hourly observations.

The buoy off the shore of Michigan City Indiana saw even larger
waves... with wave heights thus far having peaked at 12.4 ft just
after 300 am CDT Monday morning. That buoy recorded waves of 9 ft
or greater between 12 am and 6 am CDT Monday.

A few factors led to the large waves at the Michigan City
buoy... which are probably more representative of the waves
experienced along much of the Indiana shore and even parts of the
Chicago shore. First... the north winds created a long fetch... or
distance over the lake... which resulted in larger waves at the end
of the fetch. The other factor that may have contributed was the
water temperature and resultant instability. The water
temperatures at the south buoy were 5f to 7f degrees colder than
along the shore. With air temperatures nearly identical to the
water temperatures... instability was higher near the shore which
allowed for some stronger winds and larger waves than observed at
the mid lake buoy. Winds at the south buoy peaked at 35 knots... or
40 mph... between 10 PM and 11 PM Sunday night while on the shore
of Michigan City /site mcyi3/ winds peaked at 42 knots or 48 mph
between 12 am and 1 am Monday morning.

This information may be updated today to account for higher wave
heights reached at Michigan City.



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