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12 Appendix
Apparent temperature - Refer to wind chill
Dew point - Temperature point that is dependent on a specic barometric pressure,
a specic temperature and a specic humidity coinciding. At this temperature point
the humidity starts to condense and is deposited as a liquid (mist or vapour). If the
dew point for water vapour is under 0˚C, the condensation takes the form of snow or
frost.
Weather forecast - Forecast indicator using weather symbols, calculated from the
rate at which the barometric pressure rises or falls (trend).
This rate of change in the barometric pressure is the decisive factor in forecasting
the weather to come, with the absolute value playing only a minor role. As a general
rule, rising barometric pressure indicates better weather and falling barometric pres-
sure indicates poorer weather.
Wind chill equivalent temperature (apparent temperature) - This is a notional tem-
perature felt by people under certain circumstances, rather than the actual measu-
red temperature. It can be used, for example, at low temperatures (e.g. under 7˚C)
to indicate how people will actually feel at certain temperatures and wind velocities
and wearing appropriate clothing. The conditions at which the wind chill comes in to
play are when the temperature is below 33˚C and the wind velocity is over 2.6 m/s.
Thewindchillisdenedasthecoolingeectfeltonuncoveredskinwithanassu-
med constant skin surface temperature of 33˚C.
The higher the wind velocity and the lower the actual temperature, the more pro-
nouncedthewindchilleect.
The “apparent temperature” is more or less comparable to the perceived tempera-
ture,whichalsotakestheeectofthesun’srays,thereectionoflightbytheclouds
and the light wavelength, etc. into account.
Table of wind strengths (Beaufort scale)
Beaufort number Wind velocity Description
0 0 – 0.7 km/h Calm
1 0.7 – 5.4 km/h Light air
2 5.5 – 11.9 km/h Light breeze
3 12.0 – 19.4 km/h Gentle breeze
4 19.5 – 28.5 km/h Moderate breeze
5 28.6 – 38.7 km/h Fresh breeze
6 38.8 – 49.8 km/h Strong breeze
7 49.9 – 61.7 km/h Near gale
8 61.8 – 74.6 km/h Gale
9 74.7 – 88.9 km/h Severe gale
10 89.0 – 102.4 km/h Storm
11 102.5 – 117.4 km/h Violent storm
12 > 117.4 km/h Hurricane
