Appendix: Weather Data
Page 48
Vantage Pro Manual
• Wind chill
Wind chill takes into account how the speed of the wind affects our per-
ception of the air temperature. Our bodies warm the surrounding air
molecules by transferring heat from the skin. If there’s no air movement,
this “insulating layer” of warm air molecules stays next to the body and
offers some protection from cooler air molecules. However, wind sweeps
that comfy warm air surrounding the body away. The faster the wind
blows, the faster heat is carried away and the colder you feel. Above 91 F,
wind movement has no effect on the apparent temperature, so wind chill
= the outside temperature.
• Heat Index
The Heat Index uses the temperature and the relative humidity to deter-
mine how hot the air actually “feels.” When humidity is low, the appar-
ent temperature will be lower than the air temperature, since
perspiration evaporates rapidly to cool the body. However, when
humidity is high (i.e., the air is saturated with water vapor) the apparent
temperature “feels” higher than the actual air temperature, because per-
spiration evaporates more slowly.
Note:
Vantage Pro measures Heat Index only when the air temperature is above 57˚ F (14˚ C), because
it’s insignificant at lower temperatures. (Below 57˚, Heat Index = the air temperature.) The Heat
Index is not calculated above 135˚ F (52˚ C), because calculation factors are not available.
• THSW (Temperature - Humidity - Sun - Wind)
Finally, like Heat Index, the THSW Index uses humidity and tempera-
ture to calculate an apparent temperature. In addition, THSW incorpo-
rates the heating effects of direct solar radiation and the cooling effects of
wind on our perception of temperature.
Note:
The Vantage Pro displays THSW only if you have the optional Solar Radiation sensor.
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