The Weather Stress Index, or WSI, is a relative measure of the

weather Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmosphere, the ...

conditions, often used as a comfort indicator. The index, a number between 0 and 100, represents the percentage of time in the past with temperatures below the current temperature, for a given location, day and time. This makes the index a local measure based in past weather conditions. For example, if for a given location, on the 25th of July at 13:00 UTC the WSI is 85 for a temperature of , this means that the temperature was inferior to 42 °C in 85% of the time in the past, on the same place, on the 25th of July at 13:00 UTC (and superior to 42 °C in 15% of the time on the same place, day and hour). In other words, the WSI gives the probability of finding a smaller temperature in the local weather history, at a given day and time, than that of the present measurement. Therefore, high values of WSI predict a relative discomfort from excessive heat for local inhabitants.

Using the index

The same WSI for different

geographic Geography (from Greek: , ''geographia''. Combination of Greek words ‘Geo’ (The Earth) and ‘Graphien’ (to describe), literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and ...

points might not refer to the same temperature - a WSI of 99.99 for a given location near the

North Pole The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where the Earth's rotation, Earth's axis of rotation meets its surface. It is called the True North Pole to distingu ...

might refer to a temperature that, in lower

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north po ...

s, could be rated with a WSI of 50 (an average temperature) for the same day and hour.

Using the index

See also