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Beaufort Scale
The Beaufort Scale is regularly used in weather forecasts, something
of interest to all outdoor modellers.
Here is the standard table describing the wind speed and effects of
the various levels of the scale.
| Force |
Description |
Result |
Wind speed |
| Km/h |
Knots |
| 0 |
Calm |
Smoke rises vertically |
0-1 |
<1 |
| 1 |
Light air |
Wind direction indicated by smoke but not wind vanes |
1-5 |
1-3 |
| 2 |
Light breeze |
Wind noticeable, leaves move, wind vane moves. |
6-11 |
4-6 |
| 3 |
Gentle breeze |
Leaves and small twigs in constant motion. |
12-19 |
7-10 |
| 4 |
Moderate breeze |
Wind raises dust and loose paper. Small branches are
moved. |
20-29 |
11-16 |
| 5 |
Fresh breeze |
Small trees in leaf start to sway.Crested wavelets
form on inland waters. |
30-39 |
17-21 |
| 6 |
Strong breeze |
Large branches in motion, wind whistles. Umbrellas
used with difficulty. |
40-50 |
22-27 |
| 7 |
Near gale. |
Trees in motion, awkward to walk against wind. |
51-61 |
28-33 |
| 8 |
Gale |
Twigs break, hard to walk. |
62-74 |
34-40 |
| 9 |
Strong gale |
Some structural damage may occur, slates removed
etc. |
75-87 |
41-47 |
| 10 |
Storm |
Trees uprooted, considerable structural damage. |
88-101 |
48-55 |
| 11 |
Violent storm |
Widespread damage. |
102-117 |
56-63 |
| 12 |
Hurricane |
Widespread Structural damage. |
118+ |
>63 |
Wind Chill Factor
Although the weather forecast give you a good idea of just how cold
it's going to be on that slope, the actual air temperature is not the whole story: when
you are outside; a flow of air will remove heat from you and the perceived temperature
will be lower than the measured one.
The result is that you feel much colder when there is a wind, and
this table will give you some idea just how much!
This drop in perceived temperature is known as the 'wind-chill
factor', so for all you slope soarers, here's a little table that will tell you how cold
it feels when the wind-chill factor is taken into account.
The left hand column is the actual air temperature, so
find the correct one then follow the row across until you are under the wind speed. The
temperature shown there is the perceived temperature caused by heat loss due to the wind.
| Wind-chill Factor Table (in
Fahrenheit) |
| AIR TEMP |
Wind speed in mph. |
| CALM |
5 |
10 |
15 |
20 |
25 |
30 |
35 |
40 |
| 50 |
50 |
48 |
40 |
36 |
32 |
30 |
28 |
27 |
26 |
| 40 |
40 |
37 |
28 |
22 |
18 |
16 |
13 |
11 |
10 |
| 30 |
30 |
27 |
16 |
9 |
4 |
0 |
-2 |
-4 |
-6 |
| 20 |
20 |
16 |
4 |
-5 |
-10 |
-15 |
-18 |
-20 |
-21 |
| 10 |
10 |
6 |
-9 |
-18 |
-25 |
-29 |
-33 |
-35 |
-37 |
| 0 |
0 |
-5 |
-21 |
-36 |
-39 |
-44 |
-48 |
-49 |
-53 |
| -10 |
-10 |
-15 |
-33 |
-45 |
-53 |
-59 |
-63 |
-67 |
-69 |
| -20 |
-20 |
-26 |
-46 |
-58 |
-67 |
-74 |
-79 |
-82 |
-85 |
| -30 |
-30 |
-36 |
-58 |
-72 |
-82 |
-87 |
-94 |
-98 |
-102 |
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