National Weather Service Weather Forecast Office

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE CHICAGO IL
1003 PM CDT FRI JUL 6 2012 /1103 PM EDT FRI JUL 6 2012/

...OPEN WATER TEMPERATURES OF SOUTHERN LAKE MICHIGAN REACH 80
DEGREES...

THE WATER TEMPERATURE AT THE SOUTH BUOY ON LAKE MICHIGAN REACHED
80 DEGREES ON FRIDAY JULY 6TH...WHICH IS REMARKABLE WARMTH FOR THE
LAKE TO BEGIN WITH...BUT UNPRECEDENTED FOR THIS EARLY IN THE SUMMER
SEASON. MONTHLY AIR TEMPERATURES HAVE BEEN ABOVE NORMAL FOR NINE
CONSECUTIVE MONTHS IN CHICAGO...AND THAT WARMTH HAS TRANSLATED
INTO WARM WATER TEMPERATURES ACROSS THE LAKE. THE PROLONGED HEAT
WAVE OF EARLY JULY OVER THE REGION FURTHER ESCALATED THE WARMING OF
THE LAKE AS WATER TEMPERATURES ROSE 10 DEGREES BETWEEN JULY 1ST AND
6TH!

THERE HAVE ONLY BEEN SIX PRIOR EPISODES SINCE 1981 WHERE THE
SOUTH BUOY WATER TEMPERATURE HAS REACHED 80 DEGREES. THESE WERE:

PERIOD    NUMBER OF HOURS AT OR ABOVE 80    MAX WATER TEMPERATURE
-----------------------------------------------------------------
AUG 88                11                             80
AUG 95                 5                             81
SEP 96                 1                             80
AUG 01                 3                             80
LATE JUL-AUG 10       13                             80
JUL 11                 1                             80

ON FRIDAY...THE BUOY RECORDED TWO HOURLY READINGS OF 80 DEGREES.
THESE WERE THE EARLIEST 80 DEGREE WATER TEMPERATURES ON RECORD AT
THIS SITE. THIS SURPASSES THE PREVIOUS RECORD OF JULY 21ST SET BOTH
IN THE PAST TWO YEARS OF 2010 AND 2011.

WHAT IS EQUALLY AS REMARKABLE IS HOW FAR ABOVE AVERAGE THE WATER
TEMPERATURE IS. LOOKING BACK AT THE AVERAGE JULY 6TH WATER
TEMPERATURE AT THAT BUOY SINCE 1981...THAT AVERAGE IS 63 DEGREES.
THE AVERAGE ON JULY 6TH 2012 WAS 78 DEGREES...15 DEGREES ABOVE
NORMAL!

FOR POINT OF REFERENCE...THE SOUTH BUOY IS LOCATED 43 NAUTICAL
MILES EAST SOUTHEAST OF MILWAUKEE. THE WATER DEPTH IS 528 FEET.
THE WATER TEMPERATURE IS RECORDED ABOUT 2 FT BELOW THE WATER
SURFACE.

    Seen below is a look at the lake breeze on the KLOT Doppler Radar from Friday afternoon.  The lake breeze often acts as a source of cooling and relief from oppressive heat if it can push inland.  While it did so gradually on Friday afternoon, temperatures behind the lake breeze were not much of a relief due in great part to the warm water temperatures.  In addtion, dew points rose in many places behind the lake breeze.  This can be seen below in Gary's observation, where the dew point had climbed to 75°.  Dew point factors into the heat index, and thus led heat index readings to be similar if not higher than prior to the lake breeze passage.