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Weather
Weather is the current atmospheric conditions, such as air
temperature, wind speed, wind direction, cloud cover,
precipitation, relative humidity, air pressure, etc.
8.10B: global patterns of atmospheric movement influence local weather using
maps that show high, low pressures and fronts
Weather Patterns
Changes in the weather
patterns occur as the earth
tries to equalize the
temperature. The
equalization comes from
• Global Wind Currents
• Global Ocean Currents
• An air mass is a large
body of air that has
similar temperature
and moisture
properties
There are two ways
to identify air
masses. You can
identify air masses
by the amount of :
•moisture
•temperature
Using Moisture to
identify air masses:
–Continental (c) Located over large
land masses - DRY
–Maritime (m) Located over the
oceans - HUMID
Using temperature to
identify air masses:
–Polar (P) - Cooler
–Tropical (T) - Warmer
Moisture and
temperature are then
combined to describe
the air mass
–cT – Dry warm
– cP – Dry cold
– mT – Humid warm
–mP –Humid cold
Put together on a map:
30o Latitude
Tropic of
Capricorn
Fronts
• A front is the front edge
of the boundary between
air masses that have
different characteristics.
• There are different types
of fronts
– Cold Front
– Warm Front
– Stationary Front
– Occluded Front
Cold Front
• The cold dense air behind a
cold front pushes the warmer
air up forming cumulus clouds
• A cold front usually moves fast
and causes showers and
thunderstorms
Facing Fronts - Cold
• Imagine that a mass of air is sitting on top
of Canada. Like the ground below, the air
becomes chilled, in winter, it is downright
cold.
Facing Fronts - Warm
• Now consider another mass of air that
forms over the sun-baked lands of Mexico.
This air is warm!
On the move
• Air, being a gas, doesn’t just sit around, it
moves. As the air masses move, they
bring the weather with it.
• So when that Canadian air mass moves
south, it drops the temperatures of the
areas that it passes over.
• And the same with that warm front, it
raises the temperatures of land it passes
over.
Cold Front – Rapid Climb
• Since cold air is heavier than warm air, it
stays near the ground. So as the cold front
moves into a warmer region, it rapidly lifts
the surrounding warm air.
• It acts like a wedge, sending warm, moist
air up.
Cold Front – Rapid Climb
• As the warm, humid air gets pushed up, it
cools
• This quick cooling produces condensation
and precipitation.
• This is the ideal setting for a thunderstorm.
• The upward push creates rapid and violent
air currents.
• The quick cooling condenses water vapor
and produces quick intense cloud bursts.
Warm Front
Front Animations
• The warm air behind a warm fronts
pushes over the cooler air ahead of it
forming stratus clouds
• A warm front causes steady rain,
drizzle and fog
Warm Front – Slow and Steady
• Now imagine an approaching warm front.
• As this air mass moves in, it pushes the
cold front ahead.
• At the same time, it also rises above the
cold air that is already there.
• The climb above the cold air is slow and
steady – the clouds are slow to build
• When the clouds release any precipitation,
the rain or snow is long-lasting.
Stationary Front
• A stationary front occurs when a
front stops moving
• The air is unsteady and sometimes
causes rain, and showers
Stationary Front – Going Nowhere
• As the name implies, a stationary front doesn’t
move (for a while).
• If the stationary front produces rain, then the rain
continues to fall until the front does finally move.
• This type of front can lead to flooding (just as we
saw this past summer).
Occluded Front
• An occluded front occurs when two cooler
air masses merge, forcing warmer air to rise
between them
• Weather similar to a warm front
Occluded Front
• Has a mass of air that gets carried up.
• The most common occluded front occurs
during a winter storm
• Warm air gets “occluded” as it rises above
the boundary between a cool and cold air
masses.
• The jet stream is a
river of fast moving air
high in the atmosphere
that pushes fronts and
controls other weather
patterns
• Blows from west to
east at about 200 to
400 km/hr
– Airplanes are aided by
jet streams when
traveling east
BETWEEN
Pressure Systems - High
• High Pressure: higher
density air sinks and
pressure gets higher
• winds go clockwise
– good weather
– few clouds
– no rain
Pressure Systems - Low
• Low Pressure: low density
air rises, then cools. Water
vapor condenses
• winds go counterclockwise
– usually means stormy
weather
– lots of clouds
– rain is more common
Pressure Systems
Label these in your notes!
Weather Maps
• Weather maps are a combination of
analyzed data
• This data is visually represented
• In order to communicate world wide,
standard symbols have been created
• You will learn some basic symbols and
terms
Weather Map Symbols:
Fronts and Pressures
• Cold Front • Warm Front –
• High Pressure –
• Low Pressure –
• Stationary Front –
• Occluded Front -
Weather Map Symbols: Isobars
• Isobars are lines on a
map that connect areas
of equal atmospheric
pressure
• The highest wind speeds
are found where the
isobars on a weather map
are spaced closest
together
Weather Map Symbols:
Cloud cover and wind
Wind Direction
Winds are named
for the direction
that they come
FROM
Westerly Wind
Wind Symbols: Speed
Calm
Less than 5kts
5 kts
10 kts
50 kts
Now You Try It
45kts
15kts
20kts
25kts
30kts
40kts
35kts
Two types of wind representation:
• With modern systems, color is now used,
although the symbol and number system
is still used
Interpreting Weather Map Activity
Link is on teacher website