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How cold is it outside? Simply
knowing the temperature doesn't tell you enough about the
conditions to enable you to dress sensibly for all winter
weather. Other factors including wind speed, relative
humidity and sunshine play important roles in determining
how cold you feel outside. A description of the character of
weather known as "coldness" was proposed about
1940 by scientists working in the Antarctic. The "wind
chill index" as developed to describe the relative
discomfort/danger resulting from the combination of wind and
temperature.
The wind chill index
describes an equivalent temperature at which the heat loss
from exposed flesh would be the same if the wind were near
calm. For example, a wind chill index of -5 indicates that
the effects of wind and temperature on exposed flesh are the
same as if the air temperature were 5 degrees below zero
even though the actual temperature is much higher. It's a
measure of the amount of heat loss.
Wind chill does not affect
your car's antifreeze protection. It will have an impact on
how quickly your home's exposed water pipes freeze, but has
little impact on whether they would freeze or not. The
importance of the wind chill index is as an indicator of how
to dress properly for winter weather. In dressing for cold
weather an important factor to remember is that entrapped
insulating air warmed by body heat is the best protection
against the cold. Consequently, wear loose-fitting,
lightweight, warm clothing in several layers. Outer garments
should be tightly- woven, water-repellant and hooded.
Mittens snug at the wrist are better protection than
fingered gloves.
To use the chart, find the
approximate temperature on the top of the chart. Read down
until you are opposite the appropriate wind speed. The
number which appears at the intersection of the temperature
and wind speed is the wind chill index.
WIND Temperature (° F)
(mph) 35 30 25 20 15 10 5 0 -5 -10 -15 -20 -25
----------------------------------------------------------------------
5 32 27 22 16 11 6 0 -5 -10 -15 -21 -26 -31
10 22 16 10 3 -3 -9 -15 -22 -27 -34 -40 -46 -52
15 16 9 2 -5 -11 -18 -25 -31 -38 -45 -51 -58 -65
20 12 4 -3 -10 -17 -24 -31 -39 -46 -53 -60 -67 -74
25 8 1 -7 -15 -22 -29 -36 -44 -51 -59 -66 -74 -81
30 6 -2 -10 -18 -25 -33 -41 -49 -56 -64 -71 -79 -86
35 4 -4 -12 -20 -27 -35 -43 -52 -58 -67 -74 -82 -92
40 3 -5 -13 -21 -29 -37 -45 -53 -60 -69 -76 -84 -92
Wind speeds above 40 mph have little additional chilling affect
In using the table above,
values of wind chill below -10° F are considered bitterly
cold. Values of wind chill below -20° F are extremely cold
-- human flesh will begin to freeze within one minute!
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