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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
--------


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
------

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
----------

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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