Texas Almanac, 1992-1993 Page: 607

                                
Get the Feel of Texas Weather

Windchill Chart
ACTUAL THERMOMETER READING("F)
Estimated
Wind Speed
MPH        50   40    30    20     10     0   -10
APPARENT TEMPERATURE ( F)
Calm       50   40    30    20     10     0   -10
5     48.3  38.0 27.8   17.5   7.1  -3.2 -13.5
10     44.6  33.5  22.5  11.5   0.5 -10.5 -21.4
15     41.3  29.6  18.0  6.3  -5.3 -16.7 -28.1
20     38.5  26.2  14.0   1.8 -10.4 -22.3 -34.2
25     36.1  23.3  10.6  -2.1 -14.8 -27.2 -39.5
30     34.1  20.9  7.8  -5.3 -18.3 -31.0 -43.7
40     30.9  17.1  3.2 -10.6 -24.0 -37.4 -50.7
The table above was devised by Dr. Robert G.
Steadman, Texas Tech University, and was furnished to
the Texas Almanac by the National Oceanic and Atmo-
spheric Administration.
How Hot Does It Feel?
In the 40-year period from 1936 to 1975, nearly 20,000
people were killed in the United States by the effects of
General Heat Stress Index

Danger     Apparent
Category   Temperature (o F)-Heat Syndrome
1. Caution  80-90'        Fatigue possible with
prolonged exposure
and physical activity.
2. Extreme 90'-105'        Sunstroke, heat
Caution                  cramps and heat
exhaustion possible
with prolonged
exposure and
-physical activity.
3. Danger  105-130       Sunstroke, heat
cramps or heat
exhaustion likely.
Heatstroke possible
with prolonged
exposure and
physical activity.
4. Extreme Greater         Heatstroke or
Danger   Than 130'       sunstroke imminent.
NOTE: Degree of heat stress may vary with age,
health and body characteristics.

Actual
Thermometer
Reading (F)

excessive heat. The overall effect of excessive heat on
the body is known as heat stress. Important factors con-
tributing to heat stress are: (1) air temperature; (2)
humidity; (3) air movement; (4) radiant heat from in-
coming solar radiation (insolation), bright lights, stove
or other source; (5) atmospheric pressure; (6) physio-
logical factors which vary among people; (7) physical
activity; and (8) clothing.
Of the above factors, temperature and humidity
can be controlled by air conditioning. Air movement
may be controlled by fans; even a slight breeze is usual-
ly effective in reducing heat stress in hot, muggy
weather. However, at very high temperatures (above
normal body temperature of about 98.6 F.), winds
above 10 miles per hour can increase heat stress in a
shaded area by adding more heat to the body, whereas
when the body is exposed to direct sunlight the effect of
wind is nearly always to reduce heat stress. Radiant
heating can be mitigated by shielding or by moving
away from the source (for example, seeking shade).
Atmospheric pressure is not usually a significant fac-
tor; however, at very high elevations, decreased pres-
sure (and therefore decreased air supply) can contrib-
ute to heat exhaustion.
Hlow Cold Does It Feel?
Many factors enter into the feeling of coolness or
extreme cold, the temperature and wind speed being
most important. The following simplified table is based
upon more complex "Wind-Chill" indexes available
from the National Oceanic and Atmospheric Adminis-
tration (National Weather Service).
Thermometer readings are listed in the figures
across the top of the chart; the wind speeds are shown
down the left side. To determine how chilly it really
feels, get the proper column for each. Note the figure
where they cross.
Thus, a 20-degree temperature with a 20-mile-an-
hour wind is equal in chill to 1.8 degrees above zero. A
temperature of 10 degrees with a 15 mph wind is equal
to 5.3 degrees below.
A 10-mile-an-hour wind sets twigs dancing in the
trees. A 25-mile-an-hour wind sets big branches mov-
ing, and if the temperature is even cool, it sets teeth
chattering.
A chill effect of anything below 25 below zero creates
the danger of freezing for persons not properly clothed.

Heat Discomfort Chart
RELATIVE HUMIDITY(%)

0       10       20       30      40       50      60       70       80       90      100
APPARENT TEMPERATURE ('F)
70            64.8     65.6    66.4     67.3     68.1    68.8     69.6     70.4    71.1     71.8     72.5
75            70.1     71.2    72.1     73.0     73.7    74.6     75.3     76.1    77.1     78.2     79.2
80            75.6     76.6    77.5     78.4     79.4    80.5     81.7     83.0    84.7     86.4     88.3
85            79.9     81.0    82.2     83.6     85.0    86.7     88.7     91.0    93.7     96.8    100.6
90            84.0     85.5    87.1     89.0     91.2    94.1     97.0    101.0    105.4   110.8
95            88.0     90.0    92.4     95.3     98.4    102.6   107.4    113.9
100           91.8     94.6    97.8    101.7    106.6    112.7   120.4
RELATIVE HUMIDITY (%) ..
0        5       10      15       20       25       30      35       40      45       50
105           95.8     97.5    99.4    101.5    103.8    106.4   109.3    112.4    116.5   121.1    126.0
110           99.7    101.9    104.2   107.0    110.3    113.8   118.0    121.8    128.6
115          103.6    106.4    109.6   113.3    117.6    122.6   128.4
120          107.4    111.1    115.2   120.1    125.7    132.2
The table above was devised by Dr. Robert G. Steadman, Texas Tech University, and was furnished to the
Texas Almanac by NOAA.

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607

WEATHER

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