Transcript Why Do We Have Weather?

Weather
Take good notes! There will be a
quiz at the end of this
presentation.
WHY DO WE HAVE THE
WEATHER ?
 Just think about it!
 Why is there wind? Why does it blow
from one direction one day and another
the next?
 Why is it rainy one day and dry the next?
 How come it’s cold in the winter?
 How can we have hail in the summer?
 What causes snow and freezing rain?
If we were to pick one term to help
explain why we have weather, what do
you think would be a good word?
You might pick heat or sun….but another
good choice would be
Convection
Convection is the transfer of heat,
usually in gases or liquids.
After the atmosphere is warmed by radiation and
conduction, the heat is transferred throughout
the atmosphere by convection.
 Since warmed air has
more space between the
molecules, it’s less dense
and rises
 Cooled air is more dense
and tends to sink
 In general, air near the
equator tends to rise and
air near the poles tends
to sink
Weather Maps
 Notice that there are
H’s and L’s on the map
 There are also blue
lines with spikes and
red lines with half
circles
 Let’s take a closer
look!
High Pressure Areas
 When cooler air sinks
and is warmed, the
air can hold more
moisture
 This usually means
sunny skies
 Winds tend to move
clockwise around a
high
Low Pressure Areas
 When warm air rises and
is cooled, the air can not
hold as much moisture
 Often, these areas are
associated with
precipitation and stormy
weather
 Winds tend to move
counter clockwise around
the low
So, if you see a big H on the
weather map over the area you
live, you can expect fair weather
When you see a big L in your area,
there will probably be stormy
weather
Fronts and Air Masses
 An air mass is a large body of air whose
temperature and moisture are fairly
similar at a given altitude
 Fronts are boundaries separating
different air masses
 There are four different air masses that
affect the United States
The Air Masses
 cP( continental polar) : cold, dry stable
 cT( continental tropical) : hot, dry, stable
air aloft, unstable at the surface
 mP( maritime polar) : cool, moist, unstable
 mT( maritime tropical) : warm, moist,
unstable
This map shows the air mass
source regions and there paths
Ok, now we see the difference in
the air masses
 Let’s look at the different fronts and their impact on
weather
 Can you see the four different types of fronts on the
map?
Warm Fronts
 A warm front is
warm air displacing
cool air diagram
 Shallow leading
edge warm air
must “overrun”
cold air
 These are usually
slow moving
Cold Fronts
 Cold air advances into
region of warm air
 Intensity of
precipitation greater,
but short lived
 Clearing conditions
after front passes
 Usually approaches
from W or NW
Stationary Fronts
 Surface
positions of the
front do not
move
 Often a region
of clouds
Occluded Fronts
 Cold front
overtakes warm
front
 Often found close
to the low
pressure center
Ready for a little quiz?
You’ll need a sheet of paper
 Write your answers as we go
Here we go!
1.
 Winds in a low
pressure system
move _____
around the low
L
2.
 What type of
front can be
found close to
point D ?
3.
 Which of these
fronts would you
expect to have
greater
precipitation,
but be short
lived as the
front passes?
4.
 Give the name of
the air mass
that would have
the following
characteristics:
 cool, moist,
unstable
5.
That important weather word that
refers to the transfer of heat
6.
In general, air near the equator
tend to_____ ( rise or fall )
7.
 If there is a big
H on the
weather map
where you live,
would you expect
fair or stormy
weather
H
How did you do?
Let’s check the answers!
Answers
1. Counterclockwise
2. Cold
3. Cold
4. Maritime polar (mP)
5. Convection
6. Rise
7. Fair