Apparent Temperature Measures

The weather system calculates three apparent temperature values: heat index, wind chill, and the temperature/ humidity/ sun/ wind index (THSW Index).

Heat Index

The Heat Index combines the temperature with the relative humidity and gives you an idea of how hot the air "feels." It works with the concept of evaporation and the physiological processes of how your body cools itself. When the humidity is high (there is a large amount of water vapor in the air), perspiration does not evaporate quickly and your body does not cool as fast (or maybe not at all). The heat index value in this case is higher than the actual temperature. When the humidity is low, the apparent temperature will be lower than the air temperature since perspiration will evaporate quickly and cools your body.

Wind Chill

The Wind Chill takes into account how wind speed affects our perception of the air temperature. When the wind is not blowing, we radiate heat to the air surrounding our bodies thus forming a thin insulating layer of warm air. If the wind blows, it strips away this warm layer exposing your skin to the air and therefore you feel colder.

THSW (Temperature - Humidity - Sun - Wind) Index

This index incorporates all of the above variables into our perception of temperature.

Evapotranspiration (ET)

Evapotranspiration is a measure of the amount of water vapor that is returned to the atmosphere in a given area. It combines water returned from evaporation (from open water bodies or other wet surfaces) with that from transpiration (transfer of moisture from plant leaves to the atmosphere). It is expressed in inches and is calculated once per hour.