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A Review of Heat Index Extremes
PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE WILMINGTON OH
1125 AM EDT MON JUL 18 2011
...HEAT INDEX AND DEWPOINT EXTREMES FOR THE AREA...
AS A HEAT WAVE WITH EXCESSIVE HEAT INDICES BUILDS CLOSER TO THE AREA
DURING THE COMING WORK WEEK...SOME MAY WONDER WHAT THE HIGHEST
COMBINATIONS OF TEMPERATURE AND DEWPOINT HAVE EVER BEEN RECORDED
ACROSS THE AREA.
THE NATIONAL WEATHER SERVICE USES THE HEAT INDEX AS A MEASURE OF THE
APPARENT TEMPERATURE...OR WHAT IT FEELS LIKE...TO A HUMAN BEING
OUTSIDE IN THE ELEMENTS. THE HEAT INDEX WAS DEVELOPED IN 1978 BY
GEORGE WINTERLING...BASED ON WORK BY ROBERT STEADMAN. THE INDEX IS A
COMPLEX MATHEMATICAL EQUATION WHICH TAKES INTO ACCOUNT THE AMBIENT
AIR TEMPERATURE...AMBIENT RELATIVE HUMIDITY...AND MAKES ASSUMPTIONS
ON WHAT THE AIR FEELS LIKE TO A HUMAN OF AVERAGE WEIGHT/HEIGHT
WALKING IN A LIGHT BREEZE WEARING LONG PANTS AND A SHORT SLEEVED
SHIRT.
AT THE NATIONAL WEATHER SERVICE OFFICE IN WILMINGTON OHIO...THE HEAT
INDEX IS USED TO TRIGGER THE ISSUANCE OF HEAT
ADVISORIES...EXCESSIVE HEAT WATCHES...AND EXCESSIVE HEAT WARNINGS.
FOR A HEAT ADVISORY...HEAT INDICES MUST REACH 100 DEGREES
FAHRENHEIT. FOR AN EXCESSIVE HEAT WARNING...HEAT INDICES MUST REACH
105 DEGREES. FOR THE DAYTON AND CINCINNATI METRO AREA /MONTGOMERY
AND HAMILTON COUNTIES/...TWO CONSECUTIVE DAYS OF HEAT INDICES IN
EXCESS OF 100 DEGREES WILL TRIGGER THE ISSUANCE OF AN EXCESSIVE HEAT
WARNING.
SO WHAT IS THE HIGHEST HEAT INDEX EVER MEASURED AT THE 3 MAJOR
CLIMATE LOCATIONS /CINCINNATI...COLUMBUS...DAYTON/?
OBSERVATIONS FOR THESE SITES WERE ANALYZED AND FILTERED. ANY
OBSERVATION BELIEVED TO BE ERRONEOUS...OR CONTAIN AN AIR TEMPERATURE
BELOW 60 DEGREES WAS THROWN OUT. ONLY WARM SEASON /APRIL THROUGH
SEPTEMBER/ OBSERVATIONS WERE USED. ACCURATE DEWPOINT MEASUREMENTS
GO BACK TO 1930...SO THE PERIOD OF RECORD FOR THESE TABLES IS 1930
THROUGH 2011. THIS YIELDED BETWEEN 225,000 AND 250,000 OBSERVATIONS
PER SITE IN THIS STUDY.
BELOW IS A TABLE OF THE TOP 10 DAYS OF EXCESSIVE HEAT INDICES
MEASURED AT EACH OF THE THREE RESPECTIVE SITES. MULTIPLE INSTANCES
WERE NOT RECORDED...FOR EXAMPLE...IT IS IMPLIED THAT IF A SITE
REACHED A HEAT INDEX OF 115 ON A DATE...THEN THAT DATE WAS NOT
INCLUDED FOR VALUES LESS THAN 115.
COLUMBUS
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DATE/TIME TEMPERATURE DEWPOINT HEAT INDEX
----------------------------------------------------------
7/15/1995 - 1 PM 96 80 116
7/15/1980 - 5 PM 97 79 115
7/28/1930 - 3 PM 97 77 113
7/14/1995 - 3 PM 97 77 113
7/08/1980 - 2 PM 93 80 112
7/20/1980 - 2 PM 95 77 110
7/14/1954 - 5 PM 101 71 110
8/31/1951 - 6 PM 96 76 109
7/22/1934 - 2 PM 97 75 109
7/16/1980 - 5 PM 92 79 109
HEAT INDICES OF 100 DEGREES OR MORE HAVE BEEN RECORDED ON 1019
DIFFERENT HOURLY OBSERVATIONS IN COLUMBUS. ARGUABLY THE MOST
UNCOMFORTABLE DAYS /MOST INTENSE HEAT WAVE/ IN COLUMBUS HISTORY
/SINCE 1930/ OCCURRED ON JULY 14TH/15TH 1995...WHEN THE HEAT INDEX
REMAINED ABOVE 110 DEGREES FOR 4 STRAIGHT HOURS ON JULY 14TH...AND
THREE STRAIGHT HOURS ON JULY 15TH. ANOTHER EXTREME DAY WAS JULY 15TH
1980...WHEN THE HEAT INDEX REMAINED ABOVE 110 DEGREES FOR 6 STRAIGHT
HOURS.
DAYTON
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DATE/TIME TEMPERATURE DEWPOINT HEAT INDEX
----------------------------------------------------------
7/08/1980 - 3 PM 95 80 115
8/08/1980 - 4 PM 93 80 113
7/30/1999 - 3 PM 95 79 113
8/17/1988 - 4 PM 102 72 112
7/15/1980 - 1 PM 95 78 111
7/13/1981 - 1 PM 95 78 111
7/25/2005 - 2 PM 93 79 110
8/02/1980 - 4 PM 94 78 110
7/15/1995 - 1 PM 94 78 110
6/27/1978 - 5 PM 95 77 110
HEAT INDICES OF 100 DEGREES OR MORE HAVE BEEN RECORDED ON 653
DIFFERENT HOURLY OBSERVATIONS IN DAYTON. ARGUABLY THE MOST
UNCOMFORTABLE DAY IN DAYTON /SINCE 1930/ OCCURRED ON JULY 30TH 1999
WHEN THE HEAT INDEX REMAINED ABOVE 110 DEGREES FOR 7 STRAIGHT HOURS.
NO OTHER DAY COMES CLOSE. LIKE COLUMBUS...THE SUMMER OF 1980 SAW
NUMEROUS DAYS OF EXCESSIVE HEAT...WITH 4 DAYS DURING THAT SUMMER
SEEING HEAT INDICES EXCEED 110 DEGREES.
CINCINNATI
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DATE/TIME TEMPERATURE DEWPOINT HEAT INDEX
----------------------------------------------------------
6/23/1930 - 3 PM 98 78 116
7/30/1999 - 2 PM 98 77 114
7/23/1983 - 3 PM 100 75 114
7/11/2011 - 7 PM 93 80 112
7/21/1934 - 5 PM 108 64 112
8/03/1964 - 3 PM 100 74 112
7/14/1954 - 5 PM 102 71 111
7/27/1997 - 4 PM 97 76 111
7/20/1934 - 6 PM 104 68 110
7/11/1936 - 3 PM 104 68 110
HEAT INDICES OF 100 DEGREES OR MORE HAVE BEEN RECORDED ON 1837
DIFFERENT HOURLY OBSERVATIONS IN CINCINNATI. OF NOTE...WHILE 112
DEGREES WAS THE HIGHEST INDEX MEASURED ON AN OBSERVATION ON JULY 11
2011...THE HEAT INDEX ACTUALLY MADE IT TO 114 DEGREES AT 340 PM
/BETWEEN HOURLY OBSERVATIONS/ ON THE KCVG ASOS. AT THAT TIME...THE
TEMPERATURE WAS 96 AND THE DEWPOINT 79. THAT DAY FEATURED SIX
CONSECUTIVE HOURS WHERE THE HEAT INDEX REACHED OR EXCEEDED 110
DEGREES...MAKING IT ONE OF THE MOST UNCOMFORTABLE DAYS IN CINCINNATI
HISTORY SINCE 1930.
$$
- Seth Binau, Science and Operations Officer (seth.binau@noaa.gov)
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