REGIONAL WEATHER

–      Even though weather is affected by large weather systems moving across Canada, weather can also be affected by the make-up of the local environment (example: living near a lake or mountain).

–      We’re going to be looking at five factors that affect regional (local) weather.

THERMALS

–      Most winds are caused by convection.  Convection is the movement of air when the air becomes heated.

–      In the case of the Earth, the Sun is responsible for heating the air.

–      When the air becomes heated it rises higher.  As the warmer air rises, colder air moves in to replace the warm air.

–      The pattern keeps cycling and is called a convection current.

–      When the convection current occurs in a regional area during the day it is called a thermal.

–      Thermals begin to form in the morning, are present during the day, and disappear at night.

–      Why?  Because the production of thermals is dependent upon the Sun.

SEA BREEZES

–      When a thermal forms near the shore of a body of water it is called a sea breeze.

–      Water takes longer to heat up than the land does.  Due to this, the convection current moves air from the water to the land.

–      Therefore, as you sail onto a body of water, you’re going against the wind.  As you sail back to land, the sea breeze will be at your back.

LAND BREEZES

–      At night when the Sun sets, the land cools down quicker than the water.

–      Because of this, a convection current flows from the land to the water.

–      This convection current is called a land breeze.

–      Land breezes are usually very weak and this is why water by the shore is calm at night.

LAKE-EFFECT SNOW

–      When an air mass moves across a body of water, it picks up moisture from the water.

–      Therefore when the air mass reaches the southern shore of a lake, it holds a lot of moisture which results in a lot of snow in the winter.

–      For example, Toronto (North of Lake Ontario) gets about 125cm of snow during the winter while Buffalo (South of Lake Ontario) gets about 235cm of snow.

CHINOOK WINDS

–      Chinook winds occur on the eastern side of the Rocky Mountains.  They are warm, dry winds.

–      As winds coming from the west rise over the Rocky Mountains, the water vapour in the air condenses to form clouds and then rain or snow.  Therefore when the air reaches the eastern side of the mountains, the wind is very dry brings very warm temperatures.

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