What does it feel like?

No matter what season we're in there's always a difference between the actual temperature and what it "feels like". In the winter months wind-chill charts are used to calculate what the temperature feels like on exposed skin. Most people have either heard about or seen a wind-chill chart. If not, here is an example of one:

During the summer months a heat index chart is used to calculate what the temperature "feels like".  The heat index chart plots the actual temperature against the dew-point to give a temperature of what it feels like outside on exposed skin. Dew-points are important for a lot of reasons but in this case they measure the actual moisture content in the air rather than the water vapor in the air. The measure of the amount of water vapor in the air is often referred to as "Relative Humidity". This is misleading because it is not nearly as accurate as dew-points. When actual temperatures are plotted against dew-points you get a chart like this one:

This is how the NWS decides to issue a Heat Advisory or Warning. Generally speaking, dew-points in the mid 60's are considered comfortable. If you have real temperatures in the 90's and dew-points in the 70's then it typically feels like 100 degrees or more.

I hope this has been helpful. I sure wish it was 40 degrees with 2mph winds today don't you?