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Fronts Fronts • Air masses move according to global winds and currents. • The area between two air masses is known as a front. • Meteorologists have determined four main types of fronts: Cold, warm, stationary and occluded. 5 Characteristics of a Front • Sharp temperature changes over a relatively short distance. • Changes in air moisture content • Shifts in wind direction • Pressure changes • Clouds and precipitation Cold Fronts • Cold air mass reaches a warm air mass. • Because the cold air is more dense then the warm air, it pushes the warm air upwards. • Cumulus clouds or cumulonimbus clouds are often seen. • Cold fronts often bring rain, strong storms or tornadoes. Cold Fronts In the summer, cold fronts can trigger: • thunderstorms • large hail • dangerous winds • tornadoes Warm Fronts • A warm air mass reaches a cold air mass. • Warm air rises slowly over the cold air mass. • Usually forms stratus and/or nimbostratus cloulds that carry light rain or snow. • Once the air mass has passed, the temperature tends to be warmer then before. Warm Fronts Warm Fronts • Temperature – rises slowly • Pressure – slight rise, then fall • Clouds – strato- and cirro• Precipitation – long, steady • Winds – variable and light • Typically will have affect for days Stationary Fronts • A cold mass of air and a warm mass of air are in contact with no movement. • Warm air rises and condenses to form stratus clouds and usually rain. • The front can be stationnary for many days. Occluded Fronts • A cold front reaches a warm front and moves very slowly. The two air masses are blocked. • Many types of clouds are seen. • Occluded fronts generally bring a long period of hard precipitation. Occluded Fronts Fronts and their symbols • Notes – Answers • Video – Weather fronts