Published on February 27, 2008
Weather Patterns and Forecasts: Weather Patterns and Forecasts Environmental Science Changing Weather: Changing Weather Because air and moisture move in the atmosphere, weather constantly changes. It could be sunny and warm in the morning, and be cloudy and cold in the afternoon. Air masses: Air masses An air mass is a large body of air that has properties similar to the part of the Earth’s surface over which it develops. Highs and lows: Highs and lows Atmospheric pressure varies over Earth’s surface. Remember, winds blow from areas of high pressure to areas of low pressure. Large, swirling areas of low pressure are called cyclones and are associated with stormy weather. High Pressure: High Pressure Winds blow away from a center of high pressure. High pressure areas are associated with fair weather and are called anticyclones. How do you measure air pressure?: How do you measure air pressure? With a barometer. Greek for weight and measure Front: Front A boundary between two air masses of different density, moisture, or temperature. Cloudiness, precipitation, and storms sometimes occur at frontal boundaries. There are four types of fronts: cold, warm, occluded, and stationary. Cold Front: Cold Front Occurs when colder air advances toward warm air. The cold air wedges under the warm air and lifts it. The air cools and the water vapor condenses, forming clouds. When the temperature difference between the cold and warm air is large, thunderstorms and even tornadoes can form! Warm front: Warm front Forms when warmer air advances over colder air Warm air slides over the colder air with a gentle slope, unlike in a cold front where it is suddenly lifted. This gentle sloping upwards can leads to hours, if not days, of wet weather. Occluded front: Occluded front Involves three air masses of different temperatures. Cold air, cool air, warm air. The term occlusion means “closure”. Colder air forces warm air upward, forming a front that closes off the warm air from the surface. Stationary Front: Stationary Front Air masses and their boundaries stop advancing They may remain at the same place for several days producing light wind and precipitation. Severe Weather: Severe Weather Includes thunderstorms, lightning, thunder, tornadoes, hurricanes, and blizzards. Thunderstorms: Thunderstorms Occur inside warm, moist air masses and at fronts. Warm, moist air is forced rapidly upward, where it cools and condenses Strong updrafts of warm air and sinking, rain-cooled air cause strong winds. Slide26: Cumulonimbus clouds Lightning: Lightning Inside of a cloud, warm air is lifted rapidly as cooler air sinks. This movement of air can cause parts of the cloud to become oppositely charged. Current flows between the regions of opposite electrical charge, forming a lightning bolt. Thunder: Thunder Lightning can reach temperatures of about 30,000 degrees C (5 times the temperature of the surface of the sun!) The lightning superheats the air and causes the air around it to expand rapidly. Then it cools quickly and contracts. Tornadoes: Tornadoes A violent, whirling wind that moves in a narrow path over land. In severe thunderstorms, wind at different heights blows in different directions and at different speeds. This difference in wind and direction is called wind shear, and creates a rotating column parallel to the ground. A thunderstorm’s updraft can tilt the rotating column upward into the thunderstorm creating a funnel cloud. If it comes in contact with the earth’s surface, it’s called a tornado. Hurricane: Hurricane The most powerful storm. A large, whirling, low pressure system that forms over tropical oceans. Must have winds of at least 119 km/h to be called a hurricane. Blizzard: Blizzard A winter storm with strong winds, cold temperatures, and low visibility Lasts more than three hours Winds are 56 km/h or greater Visibility is less than 400 m in falling or blowing snow. Severe Weather Safety: Severe Weather Safety A watch means that conditions are favorable for severe weather to develop. A warning means that severe weather conditions already exist. Weather Forecasts: Weather Forecasts Meteorologists study and predict weather. They take measurements of temperature, air pressure, winds, humidity, and precipitation. Weather Maps: Weather Maps Data from instruments are plugged into computers to make predictions about weather patterns Data is collected from the upper atmosphere and at Earth’s surface. Information is recorded by satellites, instruments attached to weather balloons, and from radar. Station Model: Station Model Shows the weather conditions at a specific location on Earth’s surface. Isotherms: Isotherms Lines on a weather map that connect points of equal temperature. Iso means same and therm means temperature Isobars: Isobars A line drawn to connect points of equal atmospheric pressure. If they are close together, it shows a large pressure difference over a small area. A large pressure difference causes strong winds. If they are spread apart, it means a small difference in pressure (gentle winds) Can also indicate high and low pressure areas. Weather Fronts Move…: Weather Fronts Move… From West to East!!!