Relative humidity is the number most people know, but it’s a slippery one. It changes all day as the temperature changes, even when the amount of moisture in the air stays the same. On a cold morning the humidity might read 90 percent, and by afternoon it’s 40 percent, yet nothing has really changed.
Dew point is the steadier number. It’s the temperature the air would have to cool to before moisture starts condensing out as dew, frost or fog. The higher the dew point, the more moisture is really in the air.
How to use it
- Fog: when the temperature drops close to the dew point on a calm night, expect fog.
- Frost: if the dew point is below 0°C and the overnight low will reach it, expect frost on windshields and roofs.
- Comfort in summer: a dew point under 10°C feels dry and comfortable, which is typical for Lethbridge. Above 16°C starts to feel sticky. That’s why 30°C here feels very different from 30°C in Toronto.
- Storms: in summer, rising dew points ahead of a cold front give thunderstorms more fuel.
West Lethbridge Weather shows the dew point right beside the temperature. Watch how close they get overnight, and you’ll start predicting fog and frost yourself.
Related: Live conditions at West Lethbridge Weather · How to Read the Weather
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