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 = Precipitatio n. Look for fronts to find temps.

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.