Columbia Weather Systems, Inc.
59
A
DDENDUM
: W
IND
C
HILL
A
LGORITHM
To compute the wind chill, first calculate the CORRECTION FACTOR (CF) from the
following table and formulas:
Using the wind speed in mph, calculate the wind speed index. (Range is 5 to 50
mph.)
Index = 10 - Integer (Wind Speed/5)
Example: 37 mph/5 = 7 R2, where 7 = integer and 2 = remainder
Index
Table #1
Table #2
Wind Speed (mph)
0
156
0
50
1
151
16
45
2
146
16
40
3
141
16
35
4
133
25
30
5
123
33
25
6
110
41
20
7
87
74
15
8
61
82
10
9
14
152
5
10
0
0
<5
CF = Table #1 + (Table #2 * 1/16 * Remainder (Wind Speed/5)
Then compute the WIND CHILL (WC), use the following formula:
IF temperature (in °C) - 33 (or in °F -91.4) is > 0;
Then WC = (CF* (Temp. in °C - 33 (or Temp. in °F - 91.4))/256) + temperature
IF temperature (in °C) - 33 (or in °F -91.4) is < 0;
Then WC = actual temperate (there is no wind chill)
Examples:
1.
Given 25 mph and 20°C:
Index = 10 - 25/5 = 5
CF = 123 + (33 * 1/16 * 0) = 123
WC = (123 * (20 - 33)/256) +20
WC = -123 (0.05078) + 20 = 13.75° C
2.
Given 27 mph and 68° F:
Index = 10 - Integer(27/5) = 10 -5 = 5, Remainder = 2
CF = 123 + (33 * 1/16 * 2) = 127.125
WC = (127.125 * (68 - 91.4)/256) + 68 = 56.38° F
