British Columbia: Climate

The Catt-Trax2 Team — Fri, 12 Jan 2007 15:19:49 -0800

Report prepared by Rory Masters and Joe Karpinski, students in BCIT’s Fish, Wildlife and Recreation Program.

British Columbia’s climate is determined by the topography, pacific cyclones, polar air masses, a large jet stream, and the Pacific Ocean. British Columbia is a very unique province. Only here can you relax on a beach then drive two hours and be skiing on a glacier.

Air masses and flows that control our climates

During summer months the Arctic warms up and the entire weather system shifts north and weakens in strength.

The Aleutian Low. A strong low pressure system that forms in the Gulf of Alaska during the winter months. In the summer it retreats to eastern Siberia. During the winter the Aleutian Low is responsible for sending the winter storms to the Coast of British Columbia.
The North Pacific High. In the summer months the North Pacific High takes over the North Pacific Ocean and weakens the Mid-Latitude jet stream, causing the storms to shift northwards and avoid B.C.
The Polar High. The cold temperatures in the Polar Regions cause air to descend and create a high pressure system that pushes cold air outwards in winds known as the polar easterlies.
The Mid-Latitude Jet Stream. The jet stream forms where two air masses of extremely different temperature meet. The jet stream flows at high speeds about eleven kilometres above the Earth’s surface. The jet stream is much stronger during the winter months.

The Pacific Ocean

The Pacific Ocean regulates the temperature of coastal B.C. because the water stays at a fairly constant temperature year-round, which influences the temperature of the air flowing above it.

Mountains and Valleys

Mountains act as physical barriers that cause air to move up where the moisture cools and condenses thereby creating rain and snow. This is why the coastal regions get much more rainfall than any other area of the province. When the air masses flow over the Coastal Mountains and into the valley bottoms, the air has warmed up but it is also very dry. These conditions create rain shadows.

Major Climatic Zones of B.C.

The B.C. Coast

The coastal climate of B.C. is strongly influenced by the Pacific Ocean and prevailing winds. The temperature along the coast is kept “cool” in the summer and “warm” in the winter. The coastal region receives an intense amount of rain in the winter months, and is relatively calm, sunny summer months. The spinning cyclones in the Pacific Ocean during the winter push seemingly endless winter storms into B.C. creating some of the rainiest and snowiest places in North America.

Interior Plateau

The climate of this area is controlled by the Coast Mountains that block the westerly moist air flow. The Interior Plateau is nestled on the eastern side of the Coast Mountains which gives the area a much drier, continental climate. The winters in the Plateau tend to be cold and dry. The summers of the area tend to be warm and dry. The northern part of the interior plateau has a moist, cooler regime unlike the southern part of the interior plateau which has one of British Columbia’s hottest climates. The temperatures of the area during summer stay around thirty degrees Celsius and sometimes rising above forty degrees. The Interior Plateau includes the northern areas such as Williams Lake and Prince George and continues down to the southern Okanagan, Similkameen, and Thompson River valleys.

Columbia Mountains and the Southern Rockies

This area in the south-east of our province, has a climate that varies according to elevation and the orientation of the slope faces. The valley bottoms endure warm summers and are semi-arid. These areas also have cold winters. As you move up and out of the valley bottoms the climate changes due to the windward slopes of the Monashee, Selkirk, Purcell and Rocky Mountains, which will receive much higher precipitation and cooler temperatures.

Northern and Central Plateau and Mountains

The Northern and Central Plateau is an area in the northwest of British Columbia which has cool summers and cold winters. As you travel north, the climate tends to get colder and drier. The summers are short, however, the long days compensate for these conditions. A constant, yet light amount of precipitation falls on the region throughout the year.

The Great Plains

The Great Plains is an area east of the Rocky Mountains which is an extension of the plains of Alberta, Saskatchewan and Manitoba. The Great Plains endure long, cold winters and short dry summers. This part of the province has a wide range of seasonal temperatures and precipitation is at its highest during the summer months.

Catt-Trax 2 - British Columbia: Climate - Comments