Chapter 20: Air Masses, Fronts, and Instruments

AIR MASSES Definition: Body of air that is uniform (same) air temperature and water content Air masses are named after their source region (the place where they were formed) There are four major types of air masses: Continental (c) Maritime (m) Polar (P) Tropical (T)

Tropical (T) forms in warm latitudes warm air Polar (P) forms in cold extreme north & southern regions cold air Continental (c) forms over land dry air Maritime (m) forms over oceans moist air

Describe the difference between each air mass: Continental Air Mass Maritime Air Mass Describe the difference between each air mass:

Describe the difference between each air mass: Polar Air Mass Tropical Air Mass Describe the difference between each air mass:

What type of air mass? mT- Maritime Tropical Warm and Moist Air

What type of air mass? cP – Continental Polar Cold and Dry Air

What Type of Air Mass? cT – Continental Tropical Warm and Dry Air

What Type of Air Mass? mP- Maritime Polar Cold and Moist Air

Air Masses Around the World

WEATHER FRONTS Cold Warm Occluded Stationary Definition: A front occurs when two unlike air masses collide. Remember: Warm air rises while cold air sinks! Therefore, warm air is pushed up when a cold air mass moves into the area. A typical front is several km long. There are 4 basic types of fronts: Cold Warm Occluded Stationary

COLD FRONT A cold air mass takes over a warm air mass Symbol:

Cold Front Diagram Weather Conditions: Cold fronts can move fast producing thunderstorms, heavy rain, or snow. Cooler weather follows.

Cold Front

What type of clouds are formed during a cold front?

WARM FRONT Occurs when warm air mass takes over a cooler air mass Symbol:

Warm Front Diagram Weather Conditions: Precipitation over large area, usually drizzle or rain.

Warm Front

What type of clouds would you see before the rain comes?

STATIONARY Two air masses meet and neither moves. Symbol:

Stationary Front Weather Conditions: Stationary fronts move little and rain continues over long period of time.

OCCLUDED FRONT Occurs when a fast moving cold front overtakes a warm front lifting the warm air off the ground. Symbol:

Occluded Front Diagram Weather conditions: Cool temperatures and large amounts of precipitations

Occluded Front

Weather Front Symbols

WEATHER INSTRUMENTS REVIEW… Anemometer measures wind speed Wind Vane measures wind direction Barometer measures air pressure Psychrometer measures relative humidity

Barometer Anemometer Wind Vane

Where are the High and Low Pressure Systems?

WEATHER MAPS Meteorologists prepare weather maps using coded weather information they have received from numerous weather stations.

Symbols are plotted around every weather station. The cluster of symbols at each station is called a station model.

INTERPRETING MAPS After all station models are plotted, meteorologists create individual maps to observe individual weather characteristics. Lines are drawn between stations with equal values of temperature, pressure, or precipitation.

Areas of equal pressure are called isobars

Areas of equal temperature are called isotherms Areas of similar precipitation are shaded different colors or patterns to indicate the precipitation type