Introduction to Weather Fronts

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Introduction to Weather Fronts
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Air Pressure

• Air Pressure pressure due to the weight of the
  overlying atmosphere pushing down on any given
  area
• measured using barometers
• units are millibars, inches, and atmospheres
• (1 atm 1013.2 mb)
• Air pressure is often shown on weather maps by
  the use of isolines called isobars
• air pressure gradient change in air pressure
  over a distance

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Mercury Barometer
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Where is the pressure gradient the steepest on
this map?
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Effects of Weather Variables on Pressure

• Higher temperature air lower density air
  lower air pressure ( T D P )
• more water vapor in the air lower pressure
  (H2O weighs less than air nitrogen and oxygen)
• higher altitude lower pressure (remember air
  rises, expands, and cools)

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Wind

• Wind horizontal movement of air parallel to the
  Earths surface
• blows from areas of high pressure to areas of low
  pressure
• deflected by the Coriolis Effect (caused by
  Earths rotation)
• to the right in N. Hemisphere
• to the left in the S. Hemisphere

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To measure wind we use

• Anemometer measures wind speed
• Wind vane measures wind direction
• reported by the direction wind is coming from
  Wind E 5 mph

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Do you think really think the winds blow exactly
like this????
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Coriolis Effect
Winds deflect to the right in the Northern
Hemisphere Winds deflect to the left in the
Southern Hemisphere
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Lows and Highs in the Northern Hemisphere

• Lows are called Cyclones

• Highs are called Anti-cyclones

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Spin counter-clockwise and winds blow toward the
center
Spin clockwise and winds blow out from the center
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Precipitation

• Precipitation falling liquid or solid water
  from clouds
• forms when ice crystals or water become big
  enough so that they will fall by gravity
• A rain gauge is used to measure rainfall amount,
  measured in inches or centimeters
• Snowfall is measured using a ruler

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Fronts

• Fronts two air masses of different
  characteristics meet
• cold fronts push forward like a wedge, showery
  precipitation
• warm fronts are forced upward as they overtake a
  cold air mass, steady precipitation
• occluded fronts form when a cold front catches up
  to a warm front, stronger more developed storms
• stationary fronts are fronts that are not moving
  forward

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Cold Front wedge shape forcing warm air upward
Rain or snow showers
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Warm Front warm air travels up cold air like a
ramp
Steady rain or snow
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Front Symbols
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Development of Occluded Front
Occluded fronts form when a cold front catches up
to a warm front Stormy weather!! Developed storms
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