WEATHER SYSTEMS

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WEATHER SYSTEMS
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Quick Review

• What causes wind?
• Answer uneven heating of the earth by the
  sun.
• Is hot air high pressure or low pressure?
• Answer low pressure.
• What about cold air?
• Answer high pressure
• Which type of air rises? Which one sinks?
• Answer hot air (low pressure) rises, and cold
  air (high pressure) sinks.
• Now lets talk about Air Masses

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Air Masses A large body of air that has nearly
the same temperature and humidity throughout-
They have similar properties as the part of the
earths surface over which they form.
                                          
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Why are Air Masses important?

• They can cover an area of thousands of square
  kilometers.
• They are responsible for day to day weather
  changes.

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High Pressure
Low Pressure
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Which way do the winds blow?

• From ___________ pressure to _____ pressure.

high
low
Do you know what instrument we use to measure air
pressure?
A Barometer
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Cyclones

• In the northern hemisphere, once wind blows into
  a low pressure area, it rises in a
  counterclockwise direction this is called a
  cyclone. Low pressure areas usually have stormy
  weather. This is not the same as a tornado

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Anticyclones

• Wind also blows AWAY from the center of high
  pressure. In the northern hemisphere, this wind
  blows in a clockwise direction. High pressure
  areas usually have good weather.

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Fronts

• What is a front?
• It is a boundary between two air masses of
  different density, moisture, or temperature.
• There are four types of fronts can you name
  them?? _____________, ______________
• _____________, and ______________

Warm front
Cold front
Occluded front
Stationary front
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Precipitation Along a Cold Front lifting the
warm moist air ahead of it
A Closer Examination of the Animation
Initially, the cold air mass wedges into the
warmer air mass ahead of it, (separated from each
other by the cold front). The lighter warm air is
lifted upwards by the denser cold air and if
enough water vapor condenses, clouds develop.
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Precipitation Along a Warm Front warm moist air
overriding colder air
A Closer Examination of the Animation
Initially, a warm air mass (in yellow) nudges
against a colder air mass (in blue) ahead of it,
(separated from each other by the warm front).
The lighter warm moist air behind the front is
lifted upward and "overrides" the colder air.
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Stationary Front
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SEVERE WEATHER
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Thunderstorms
What is a thunderstorm?

• - A thunderstorm is a weather event where there
  is heavy rain, lightning, thunder roars, and
  possible hail.
• How do they form?
• They occur in warm moist air masses and along
  fronts.
• The air is forced upward where it is __________,
  and condensation occurs forming
  _________________clouds.
• Then __________________ happens in the form of
  rain or hail. The rain cooled air sinks and
  strong updrafts of warmer air causes strong
  winds.

cooled
cumulonimbus
precipitation
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Can thunderstorms cause damage?

• YES!
• How?
• By flooding
• Hail damage
• Wind damage
• Lightning strikes

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Lightning can also form within or between clouds,
not just from the cloud to the ground
Lightning also forms within and between clouds.
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What causes thunder ?
Which do you think is hotter, a bolt of
lightning, or the surface of the sun?
Lightning- it is 30,000 degrees Celsius. Thats 5
times hotter than the sun!!
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Can you tell how far away a thunderstorm is?
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TORNADOES
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The Fujita Scale The Fujita Scale
F0gale tornado40-72 mph Some damage to chimneys breaks branches off trees pushes over shallow-rooted trees damages sign boards.
F1moderate tornado73-112 mph Lower limit is the beginning of hurricane-force winds. Peels surface off roofs mobile homes pushed over moving autos pushed off roads.
F2significant tornado113-157 mph Roofs torn off frame houses mobile homes demolished boxcars pushed over, large trees snapped or uprooted light-object missiles generated.
F3severe tornado158-206 mph Severe damage. Roofs and some walls torn off well-constructed homes trains overturned most trees in forest uprooted heavy cars lifted off the ground and thrown.
F4devastating tornado207-260 mph Well-constructed homes leveled structures with weak foundations blown off some distance cars thrown and large missiles generated.
F5incredible tornado261-318 mph Phenomenal damage. Strong frame homes disintegrate or lifted off foundations and carried considerable distance trees debarked.
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Where are tornadoes most likely to occur?
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HURRICANES
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What is a hurricane?A hurricane is a huge storm!
It can be up to 600 miles across and have strong
winds spiraling inward and upward at speeds of 75
to 200 mph. Hurricanes usually lasts for over a
week, moving 10-20 mph over the open ocean.
Hurricanes gather heat and energy through contact
with warm ocean waters. Evaporation from the
seawater increases their power. Hurricanes rotate
in a counter-clockwise direction around an "eye."
The center of the storm or "eye" is the calmest
part. It has only light winds and fair weather.
When they come onto land, the heavy rain, strong
winds and large waves can damage buildings, trees
and cars. Similar storms are called typhoons in
the Pacific Ocean and cyclones in the Indian
Ocean.
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How do hurricanes form?Hurricanes form over warm
ocean water of 80F or warmer. The atmosphere
must cool off very quickly the higher you go. The
wind must be blowing in the same direction and at
the same speed to force air upward from the ocean
surface. Winds flow outward above the storm
allowing the air below to rise. Hurricanes
typically form between 5 to 15 degrees latitude
north and south of the equator. The Coriolis
effect is needed to create the spin in the
hurricane.                                     
                                 
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      Saffir-Simpson Hurricane Scale
                 
Category Winds (MPH) Storm Surge(Feet) Damage
1 74-95 4'-5' Minimal
2 96-110 6'-8' Moderate
3 111-130 9'-12' Extensive
4 131-155 13'-18' Extreme
5 gt155 gt18' Catastrophic

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Can Hurricanes cause damage?

• Absolutely!
• Storm surges usually cause the most damage and
  death
• Winds can destroy homes and uproot trees
• Extensive rain can also cause major flooding

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What is a storm surge?
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How do blizzards form?A blizzard is a
long-lasting snowstorm with very strong winds and
intense snowfall. You need three things to have a
blizzard cold air at the surface, lots of
moisture, and lift. Warm air must rise over cold
air. Blizzards have winds of at least 56 km/h,
temperature is below 20 degrees fahrenheit, and
visibility is less than 400 meters
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Forecasting Weather

• What information do you need to know to forecast
  weather??
• Temperature
• Winds
• Air pressure
• Humidity
• Precipitation

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Do you know the scientific name for a weather
forecaster?
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A Meteorologist is what theyre called.

• Meteorologists measure temperature, air pressure,
  winds, humidity, and precipitation.
• They use Doppler radar, satellites, and
  instruments attached to balloons to get their
  information.
• They gather information from the upper
  atmosphere, as well as from the earths surface.

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STATION MODEL
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Key to Features 1 -- Cold Front 2 -- Warm Front 3 -- Stationary Front 4 -- Occluded Front 5 -- Trough ("TROF")          Also used to depict Outflow Boundary ("OUTFLOW BNDRY") 6 -- Squall Line 7 -- Dry Line 8 -- Tropical Wave ("TRPCL WAVE")
A hash mark denotes a change in frontal type, as
in the example below.                           
          Note The hash mark will always be
drawn perpendicular to the boundaries. They are
not drawn at "triple points" (the intersection of
an occluded, cold and warm or stationary front)
and where a low pressure center separates the
different frontal types
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A weather map showing surface-pressure systems,
air masses, fronts, and isobars (in millibars) as
solid gray lines. Large arrows in color show air
flow. (Green-shaded area represents
precipitation.) Isotherms are similar to isobars,
except they show temperature (Not Shown here)
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QUESTIONS ???