Atmospheric Pressure and Fronts

Integrated Science

Atmospheric Pressure

• The pressure exerted by the molecules in the atmosphere.

• Weather maps classify areas as either high or low pressure– High pressure usually means no precipitation.• Shown as an H on a weather map

– Low pressure means precipitation.• Shown as an L on a weather map

Formation of Clouds

1. Water evaporates.2. The water vapor rises in the atmosphere and

cools, forming a liquid again.3. The condensed water forms tiny water

droplets.4. Lots of tiny water droplets become a cloud.

Formation of Clouds

• Cloud type formed depends on…– The amount of water droplets– How high the water droplets rise in the

atmosphere.– The temperature of the water droplets.

What is a Front?

• Fronts form at the front a mass of air.• They usually separate two masses of air that

are different temperatures. • Shown as lines with shapes on a weather map.• Meteorologists use fronts to predict the

weather.

Front Movement

• The movement of fronts show the movement of air masses.

• As a front moves over an area, the area’s temperature changes to the temperature of the air mass.

Four Types of Fronts

• Warm Fronts• Cold Fronts• Occluded Fronts• Stationary Fronts

Warm Front

• The boundary in front of a warm air mass.• Usually follow cold air masses.

Cold Front

• A boundary in front of a cold air mass.• Usually follows warm air masses.

Occluded Front

• When a cold front completely passes a warm front, an occluded front is formed.

• Usually don’t lead to any precipitation.

Stationary Front

• When any type of front stops moving it is called a stationary front.

• Weather doesn’t change for long periods of time.

The movement of Fronts

• Not all air masses move at the same speed, so some fronts will catch up with other slower moving air masses.

• When fronts meet, clouds usually form and sometimes precipitation occurs.– Thunderstorms are usually made from cold fronts

catching up to warm fronts.

Predicting Weather

• Low Pressure = Precipitation.

• Look for fronts to find temps.

Predicting Weather

Predicting Weather

Predicting Weather

• Low Pressure = Precipitation• High Pressure = No Precipitation• Cold Front = Behind the front is cooler temps.• Warm Front = Behind the front is warmer

temps.• Occluded Fronts = Not much precipitation and

temp varies. • Stationary Fronts = Weather does not change.