THW and THSW Indexes

At higher temperatures — starting around 34 °C — wind can actually intensify the sensation of heat rather than relieve it. While we usually think of wind as cooling, it can accelerate sweat evaporation so much during extreme heat that it feels even warmer.

In winter, the THW index closely matches the wind chill. In summer, it aligns well with the heat index. Weather models often display the THW index as the "feels like" temperature, with the emphasis depending on the season or whether the measured temperature is above or below 10 °C.

Sunlight can significantly influence how warm we feel. In freezing weather, sunshine can make it feel more pleasant — while in hot, humid conditions, it adds to discomfort and heat stress.

The THSW index is usually slightly higher than the THW index when the sun is shining. Without solar radiation, the THSW index tends to be a bit lower. The calculation is based on global solar radiation (in W/m²), not the number of sunshine hours.

Both indexes are shown on the Davis Vantage Pro2 console and in the associated software. A suitable formula or reference table to display these indexes on this site will hopefully be added later.