Transcript precipitation

Have you ever just looked
at clouds?
 Why do we
have clouds?
 Why are there
different
shapes?
 What can they
tell us about
the weather?
Take Good Notes!
 There will be
a quiz on
this
information
Understanding Clouds
 Clouds form as
warm air is
forced upward
 As the air is
forced upward,
it expands and
cools
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
Pressure’s Affect
L
H
L
WRECCC
Clouds
Condenses
Cools
Expands
Rises
Warm Air
How Else Can Clouds Form?
 Fronts: When a WARM FRONT RISES
OVER A COLD FRONT. This produces non
violent rain showers.
 Fronts: When a COLD FRONT RISES
OVER A WARM FRONT. This produces
possibly violent rain storms very quickly, but
is brief and may last only part of the day.
Before
Cold
Front
After
Cold
Front
 Orographic Uplift: When air is forced up the
side of a mountain or plateau. The air
forced up then cools down very quickly and
condenses to form rain clouds.
Understanding Clouds
 As the air cools,
the relative
humidity
reaches 100%
 For more information on
Relative Humidity click ☼
Water vapor begins to condense
in tiny drops around nuclei.
Nuclei are small particles of dust,
salt, and smoke in the
atmosphere
Cloud Types
 There are
many
different
cloud types
Cloud Types
 Can you think
of the two
main ways
that clouds
are classified?
 Shape, Height,
and
sometimes
Rain Capacity
By Shape!
 There are three main cloud
types that are based on shape
 Think you know any of them?
 Stratus
 Cumulus
 Cirrus
Stratus Clouds
 Stratus
clouds form
a smooth,
even sheet
 They usually
form at low
altitudes
Stratus Clouds
 When air is
cooled and
condenses near
the ground, a
stratus cloud
know as _______
forms
 Know the
name?
Fog
 Fog forms when a cold surface cools the
warmer moist air above it.
 What is water vapor doing in the air to
form fog?
– Condense
 At what temperature does the air hit to
condense as fog?
– Dewpoint
Cumulus Clouds
 These are
masses of
puffy, white
clouds, often
with flat bases
 They form
when air
currents rise
Cumulus Clouds
 They can be
associated
with both fair
weather
and…….when
they get really
tall!?!?!
Thunderstorms!
Cirrus Clouds
 Cirrus clouds
are high, thin,
white,
feathery
clouds
containing ice
crystals
Cirrus Clouds
 Cirrus clouds
are usually
associated
with fair
weather, but
they may
indicate
approaching
storms
By Height
 The prefix of cloud names can
describe the height of cloud
bases
 Cirro: High clouds above
6000m
By Height
 Alto: Middle elevation clouds
between 2000 to 6000m
 Strato: Low level clouds below
2000m
Rain Clouds
 Nimbus
clouds are
dark clouds
associated
with
precipitation
Rain Clouds
 When a nimbus
cloud is also a
towering
cumulus cloud,
it’s called a
cumulonimbus
cloud
Ready for a quick review?
 1. Clouds can form when the
relative humidity reaches ____%
 2. In order for clouds to form,
water vapor begins to condense
around ____of dust, salt, and
smoke
 3. Clouds are classified by ____
and____ and sometimes rain
capacity
 4. Puffy, white clouds are called?
 5. Mid elevation clouds between
2000 and 6000m
Let’s see how you did!
1. 100
2. Nuclei
3. Shape and height
4. Cumulus
5. Alto
Forms of Precipitation
 Precipitation (pre-sip-uhtay-shun) is any form of
water that falls to the
Earth's surface.
Types of Precipitation
 The type of precipitation that
falls to the ground depends
upon the formation process
and the temperatures of the
environment between the
cloud and the surface
Can you name the different
types of precipitation?
 Rain
 Snow
 Hail
 Sleet
 Freezing Rain
Rain
Rain develops when
growing cloud droplets
become too heavy to
remain in the cloud and
as a result, fall toward the
surface as rain

 Rain can also
begin as ice
crystals that
collect each
other to form
large
snowflakes
 As the falling
snow passes
through the
freezing level
into warmer
air, the flakes
melt
Rain from snow!
Snow
 Snow is formed when ice
crystals form from water
vapor that is in the clouds
directly above your heads!
 This process is called
sublimation
Hail
 Hail is formed
when updrafts
carry raindrops
upwards into
extremely cold
areas of the
atmosphere
Hail
 There the
raindrops
merge and
freeze. When
the frozen
clumps get to
heavy they fall
to earth
Hail
 Hail can vary
in size, from
the size of a
small stone to
that of a
baseball! So
be careful
Sleet
 Sleet is frozen raindrops.
Sleet begins as rain or snow
and falls through a deep
layer of cold air that
contains temperatures below
freezing that exist near the
surface.
Sleet
 Rain that falls
through this
extremely cold
layer has time
to freeze into
small pieces of
ice
Freezing Rain
 Freezing rain is falling rain that
cools below 0°C, but does not
turn to ice in the air
 The water is “supercooled”
When the drops hit anything
they instantly turn to ice!
1. Nuclei for the formation of rain
drops can be small particles of: A)
salt, B) smoke, C) dust, D) all the
above
2. Which of these cloud types is not
based on the clouds shape: A)
stratus, B) nimbus, C) cumulus,
D) cirrus
3. Mid elevation clouds between
2000 and 6000m: A) nimbus, B)
alto, C) cirro, D) strato
4. This form of precipitation is
supercooled: A) rain, B) snow,
C) sleet, D) freezing rain
5. This form of precipitation
stays frozen all the way to the
ground: A) rain, B) snow, C)
sleet, D) freezing rain
Let’s see how you did!
The Answers!
1. D
2. B
3. B
4. D
5. B
Humidity and Relative Humidity
 Humidity is the amount of
water vapor in the air
 Relative humidity is a measure
of the amount of water vapor
that the air is holding,
compared to the amount it can
hold at a specific temperature
Humidity and Relative Humidity
 When the air is holding as
much moisture as it can, it’s
said to be saturated
Can you explain this graph?
 In the cool of the morning, the
air can’t hold as much
moisture. We often have dew on
a summer morning
 Once the air has warmed, the
relative humidity drops since
the air can hold more moisture
You’ve seen water on the outside
of a cold drink?
 The cold air
around the
glass causes a
lower
temperature
at which the
air is
saturated
You’ve seen water on the outside
of a cold drink?
 The
temperature
at which air is
saturated and
condensation
takes place is
the dew point
 To return click
here ☼