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Fronts Information The intersection of two air masses with different properties is called a FRONT Image from: http://www.public.iastate.edu/~mt206/ The four types of fronts are shown here: Front Symbols: (1) COLD COLD FRONT (3) STATIONARY STATIONARY (2) WARM (4) OCCLUDED WARM FRONT STATIONARY FRONT OCCLUDED FRONT The “lumps and teeth” teeth” are ALWAYS pointing the direction the front is moving! Cold Front What direction are the fronts moving? http://www.public.iastate.edu/~mt206/ Criteria for locating a front: (1) Temperature change over a short distance (2) Dew point change over a short distance (3) Shift in wind direction (4) Clouds and Precipitation Warm Front Image from: http://www.public.iastate.edu/~mt206/ General Patterns: Warm Front: Cold Front: • Warm air moves into an area that has cooler air. • Cold air moves into and area that has warmer air. • Warm air moves up and over cooler air at a gentle angle. • Cold air forces its way under warmer air causing the warm air to rise rapidly at a steep angle. • Has different weather patterns dependent upon the stability of the air. • Precipitation occurs BEFORE the front passes. • Generally high winds and rapid drop in temperature. • In stable air precipitation is generally steady light to moderate rain for long periods. • Precipitation can be heavy and often has thunderstorms. • General cloud types stable air: cirrus, cirrostratus, altostratus, nimbostratus, stratus, stratocumulus as the front approaches and passes. • In unstable air can develop heavy rain and thunderstorms for long periods. • Generally move slowly (~ 15 mph) • Precipitation occurs AFTER the front has passed. • Move very rapidly (~ 40 mph) • General cloud types: Cirrus, cirrostratus, altocumulus, cumulonimbus and cumulus as the front approaches and passes. Stationary Front: Occluded Front: • Occurs when a front stops moving. This occurs because upper air flow is parallel to the boundary between warm and cool air rather than at an angle to it. •Generally thought of as a “cold front catching up to a warm front” front” • Stationary fronts can bring several days of light to moderate rain or snow. • Associated weather is similar to a warm front as the occluded front approaches. •once the front has passed, the associated weather is similar to a cold front. •There are two types of occluded fronts: • A Warm occlusion when the air behind the front is warmer than the air ahead. • A Cold occlusion when the air behind the front is colder than the air ahead. Most common type.