Download Grade Eight Notes on Weather Maps

Science 10_Notes on Weather Maps_ Name: _______________Blk:____
Low Pressure System - An area of relative pressure minimum with converging
winds, rotating in the same direction as the earth. This is counterclockwise in the
Northern Hemisphere and clockwise in the Southern Hemisphere.
High Pressure System - An area of relative pressure maximum that has
diverging winds and a rotation opposite to the earth's rotation. This is clockwise
the in Northern Hemisphere and counterclockwise in the Southern Hemisphere.
Fronts are the boundaries between air masses. A front is defined as the
transition zone between two air masses of different density. Fronts extend not
only in the horizontal direction, but in the vertical as well. Therefore, when
referring to the frontal surface (or frontal zone), we refer to both the horizontal
and vertical components of the front.
There are three main types of fronts:
Cold Front: The weather map symbol for a cold front is a blue line with triangles
pointing in the direction the cold air is moving. The cold air that's arriving behind a
cold front is a cool or cold air mass. But, you often hear it called the "cold front."
The temperature difference across the front can be small. As a cold front moves
into an area, the heavier, cool air pushes under the lighter, warm air it's replacing.
The warm air-cools as it rises. If the rising air is humid enough, water vapor in it
will condense into clouds and may fall as precipitation (fog, rain or snow).
Warm Front: The weather map symbol for a warm front is a red line with
semi-circles pointing in the direction that warm air is moving. Warm fronts often
form to the east of low-pressure centers, where southerly winds push warm air
northward. As the warm air advances northward it rides over the cold air ahead of
it, which is heavier. As the warm air rises the water vapor in it condenses into
clouds that can produce rain, snow, sleet or freezing rain, often all four. The warm
front symbol on a weather map marks the warm-cold boundary at the earth's
surface.
Stationary Front: Since neither the warm air nor the cold air are advancing,
the stationary front weather map symbols combine both the cold front and the
warm front symbols. The stationary front is shown on a map with alternating
triangles pointing away from the cold air and half circles pointing away from the
warm air. Color maps alternate the cold front blue and warm front red.