F.Y.I.

Weather Glossary

Dewpoint: The temperature at which a parcel of air would have to be cooled to reach saturation (100% humidity)

A practical way to think of dewpoint is: The temperature at which fog or dew will form. Temperatures are most likely to cool to the dewpoint around sunrise, making that the most likely time to encounter dense fog and heavy dew.

Dewpoint is a better way to guage the amount of water vapor in the air than using relative humidity. Relative humidity is relative to the actual air temperature. For example 100% humidity at 40(F)degrees is less total water vapor than 100% humidity at 90 degrees. With dewpoint, the closer the dewpoint to the actual air temperature the higher the moisture. During the summertime, dewpoints in the mid and upper 60s is an indication of very muggy and sticky air, whereas dewpoints in the 30s will be much more comfortable.

Dewpoints are very important in forecasting severe weather in the spring. The higher the dewpoint the higher the potential for severe weather. If dewpoints reach the 60s on a spring afternoon there is a lot of fuel for thunderstorms in the air.
Forecasters often look at dewpoint readings at weather observation sites across Texas to determine where drylines are.

John Cameron