Dew & Fog

Water CycleEvaporation, transpiration +

condensation

Evaporation rate greatest at equator

Dew Point vs. DewAir can hold water vapour =

humidity

Dew Point vs. DewAbsolute Humidity – amount of

water vapour in the air

Relative Humidity - % of water in the air

Dew Point vs. DewWhen the air cannot hold anymore

vapour it is 100% saturated

This is the Dew Point

Dew Point vs. DewAt the Dew Point – water vapour

condenses

Warmer the air temperature, higher the dew point

Dew Point vs. DewCondensed water vapour = dew

When it freezes = frost

FogWhen air close to the ground cools

enough & reaches the dew point

Water vapour can form a low cloud

Radiation Fog & Advection Fog

Radiation FogForms during cloudless & windless

nights

low lying fog

Radiation FogAt night, ground cools rapidly

Cools the air

Air reaches dew point, condenses into fog

Advection FogNeeds air to be moving (wind)

Warm, moist air moves over a cool surface (snow or water)

Advection FogCan cause problems in Vancouver,

Victoria, Seattle, San Francisco