Transcript Weather Patterns 11-2

Weather Patterns
11-2
OBJECTIVE: TO KNOW SEVERAL FACTORS
DRIVE CHANGES IN WEATHER.
The Changing Weather
How is weather affected by the movements of air masses and pressure changes?
 When air masses travel, they
can transport heat and
water vapor, which can
affect weather.

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Ex: cool mist air
Cold dry air
Warm moist air
Hot dry air
Weather Fronts
 A cold front: Can move
quickly. Thunderstorms
often form as warm air is
suddenly lifted up over
cold air.
 A warm front: When
warm air slides over
colder air. This can lead
to hours, if not days, of
wet weather.
Highs and Lows
 Low Pressure: Recall that
when warm air rises , it
creates a decrease in
pressure close to Earth’s
surface. Therefore a low
pressure area is created.

Ex: Cloudy stormy
weather.
 High Pressure: When
cold air sinks, it moves
closer to Earth’s surface
and an area of high
pressure is created.

Ex: Fair- good weather.
Weather Maps
 Provide info on the
atmospheric conditions
over any area of interest.
Cycles that Affect Weather
 Day & Night Cycles: As the
sun comes up it warms the
ground. The ground warms
the air by conduction.
Sometime in the
afternoon the ground and
air begin to lose energy and
starts to cool.
By the evening the or
early morning, the coldest
air is found next to the
ground.
 Seasons: The tilt of
Earth’s axis causes
seasons on Earth.

There are 4 seasons.
Fall
 Winter
 Spring
 Summer

 El Nino:
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Both northern hemisphere
jet streams shift
northward during an El
Nino.

In US this often leads to
warmer than usual
temperatures in the North
and increased rain and
flooding in the south.
 La Nina:

Happens when sea surface
temps. In the eastern
equatorial Pacific are
colder than normal.
This produces colder than
normal winter temps in
the northwestern US.
 And warmer than usual
winter temps in the
southeastern US.

Severe Weather
 Droughts: A period of
time when rain is much
lower than usual. Can
last months to years.

Affects agriculture and
can lead to wild fires.
 Floods: Too much rain
fall or rapid snow melt.
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Flash floods are the most
dangerous because can
happen in a instant
without warning.