VOLUME II9 Number 47
3 December 1962
EQUIV.\LENT TEMPERATURE
With the winter weather here and the participation in the winter sports, the
following information is being printed concerning equivalent temperatures.
For several weeks an equivalent temperature has been included on the forecast
as an aid or guide to those working or spending leisure hours outdoors or in
exposed areas. This temperature is computed from the rate of heat removal from
exposed flesh under various wind and temperature conditions. Fne actual rate
of heat loss is commonly called the Chill Factor and is expressed in kilogram
calories/square meter/nour. Since the units involved in the chill factor would
be meaningless to a mojority of personnel an equivalent temperature has been
used to indicate that rate of cooling and bettor depict the conditions which
are to be encountered.
In order that this information may better be utilized, a brief explanation of
what the equivalent temperature represents follows in the form of an example.
For instance, with 20 knots of wind and an air temperature of 45 decrees Fahren
heit the rate of heat removal from the exposed flesh is 800 kg cal./m2/hr. The
same rate of cooling is not encountered at 2 knots of wind until the temperature
drops to 13 degrees. In this instance, the equivalent temperature shown on the
forecast would be 13 degrees, and would indicate that one above conditions would
be equivalent to those encountered by someone out for a stroll on a calm.day
with the temperature 13 degrees Fahrenheit#
Simply, 45 degrees Fahrenheit with 20 knots of wind is the same as 13 degrees
Fahrenheit with 2 knots of wind.
Briefly the equivalent temperature to be used on tnc forecast is a temperature
at 2 knots of wind which will produce the same rate of heat removal from exposed
flesh as would be produced by the forecast wind and temperature®
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