Weather –

the condition of the atmosphere at a certain time and place.

Created mainlyby uneven heatingof earth’s surface

Changes in Weather

Changes in weather are caused by movements of air masses, which are large bodies of air that have the same temperature and moisture throughout.

An air mass gets is moisture and temperature from the area over which it forms called source regions.

Example: an air mass that forms of the Gulf of Mexico is warm and wet because this area (source region) is warm and has lots of water that evaporates into the air.

Air Mass Moisture Classifications

Maritime (m) – forms over water (moist)

Continental (c) - forms over land (dry)

Air Mass Temperature Classifications Arctic (A) or Antarctic (AA) – forms over

the poles (very cold)

Polar (P) – forms over polar region (cold)

Tropic (T) forms over tropics (warm)

Equatorial (E)- forms over equator (hot)

Humidity

The amount of water vapor in the air

If Earths air didn’t contain as much humidity as it does, our weather would be like that of Mars: No clouds (except dust), no rain, sleet or snow, no thunder and lightning, no fog.

And, without all of this water in all of its forms, Earth’s life, if there were any at all, would be as hard to find as signs of life on Mars.

Fronts

-occur when 2 air masses meet.

Types of Fronts: Cold front Warm front Stationary front Occluded front

Cold front

Cold front – a cold air mass moves under the less dense warm air mass and pushes it upward, away from the earth’s surface creating a cooler climate.

Warm front

– a warm air mass moves over the cold gradually replacing the cold air mass creating a warmer climate.

Stationary front – a cold air mass and a warm air

mass meet and nothing happens because the cold air does not have enough force to move the warm air mass. The climate associated with a stationary front is much like a warm front.

Occluded front – a warm air mass is caught between

2 cold air masses both of which push the warm air mass upward. The climate has cool temperature and large amounts of rain or snow.

Front Symbols

Wind

Is created by the uneven heating of the earth

Hot air rises, cold air sinks and rushes across land to replace the hot air (convection)

Jet Stream

a current of fast moving air found in the upper levels of the atmosphere. Jet streams form along the upper air boundaries of large masses of warm and cold air.

These winds not only steer storms, but also help determine the locations of areas of high and low air pressure at the Earth's surface.