Above is a heat index (or
apparent temperature) chart showing various combinations of
air temperature versus relative humidity.
To use the chart, locate the air temperature along
the left column and the relative humidity along the
top. The cell where the two intersect is the heat
For example, an air temperature of 90° F and
a relative humidity of 60% intersect at a heat index
of 100°. In other words, the temperature would feel
like 100° with this humidity/temperature
Heat index values were devised for shady light wind
conditions. Exposure to full sunlight can increase values by
up to 15° F.
First aid treatment suggestions for heat-related illnesses
can be obtained from local red cross offices, hospitals,
clinics, public health agencies and physicians.
How the heat index is computed. The heat index is
computed using an equation that was developed from data arrived
at from experience. The resulting equation is quite long with
the variable t representing the current air temperature and r
representing the current relative humidity. With t and r known,
the heat index can be calculated as follows.