Weather Patterns and Forecasts

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Weather Patterns and Forecasts

• Environmental Science

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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.

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Air masses

• An air mass is a large body of air that has
  properties similar to the part of the Earths
  surface over which it develops.

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Highs and lows

• Atmospheric pressure varies over Earths 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.

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High Pressure

• Winds blow away from a center of high pressure.
• High pressure areas are associated with fair
  weather and are called anticyclones.

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How do you measure air pressure?

• With a barometer.
• Greek for weight and measure

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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.

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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!

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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.

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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.

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Stationary Front

• Air masses and their boundaries stop advancing
• They may remain at the same place for several
  days producing light wind and precipitation.

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Severe Weather

• Includes thunderstorms, lightning, thunder,
  tornadoes, hurricanes, and blizzards.

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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.

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Cumulonimbus clouds
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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.

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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.

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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 thunderstorms updraft can tilt the rotating
  column upward into the thunderstorm creating a
  funnel cloud.
• If it comes in contact with the earths surface,
  its called a tornado.

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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.

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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.

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Severe Weather Safety

• A watch means that conditions are favorable for
  severe weather to develop.
• A warning means that severe weather conditions
  already exist.

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Weather Forecasts

• Meteorologists study and predict weather.
• They take measurements of temperature, air
  pressure, winds, humidity, and precipitation.

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Weather Maps

• Data from instruments are plugged into computers
  to make predictions about weather patterns
• Data is collected from the upper atmosphere and
  at Earths surface.
• Information is recorded by satellites,
  instruments attached to weather balloons, and
  from radar.

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Station Model

• Shows the weather conditions at a specific
  location on Earths surface.

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Isotherms

• Lines on a weather map that connect points of
  equal temperature.
• Iso means same and therm means temperature

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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.

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Weather Fronts Move

• From West to East!!!