Download cirro describes clouds that form at high altitudes, example

Understanding Weather
Chapter 16
Section 1
I. Water in the Air
I. Water in the Air
A. Weather
1. Condition of the atmosphere at a certain time
and place.
2. Affected by amount of water in the air.
B. Water cycle is the continuous movement
of water (liquid, solid or gas) from Earth’s
surface like lakes, oceans, and plants
into the air, onto and over land, into the
ground and back to the oceans and rivers.
1. Condensation occurs when water vapor
cools and changes from gas to liquid.
Clouds form this way
2. Evaporation occurs when liquid water
changes into water vapor, which is a gas
3. Precipitation occurs when rain, snow,
sleet, or hail falls from clouds to Earth’s
surface
4. Runoff is water, usually from precipitating,
that flows across land and collects in rivers,
streams, and eventually the ocean
II. Humidity - amount of water vapor in the
air
1. Invisible
2. As water evaporates and becomes
water vapor, humidity of air increases
3. Airs ability to hold water vapor
changes as temperature of air
changes.
4. As temperature air increases, air’s
ability to hold water vapor increases.
(warm air can hold more water vapor
than cold air can)
A. Relative Humidity
1. Amount of water vapor in air
compared with maximum amount of
water vapor that air can hold at certain
temperature.
2. Expressed as percentage.
3. When air holds all of the water it can at
given temperature said to be saturated and
has relative humidity of 100%
a. 50% relative humidity means the air
is holding half the amount of water
vapor it can
b. 100% relative humidity is called
saturation
B. Factors Affecting Relative Humidity
1. Amount of water vapor and
temperature
2. Constant temperature and pressure,
as amount of water vapor changes,
relative humidity changes
2. Constant temperature and pressure,
amount of water vapor changes, relative
humidity changes
3. More water vapor in air, higher relative
humidity
4. If water vapor in air stays same but
temperature changes, relative humidity
changes.
5. Relative humidity decreases when
temperature rises
6. Relative humidity increases as the
temperature drops.
III. Condensation
Process when a gas (like water vapor)
changes to a liquid.
1. Air must be saturated before
condensation can occur which means air
must be saturated
2. This means the air is at relative humidity
of 100% also know as dew point
3. Condensation occurs when saturated air
cools.
A. Dew Point - Temperature at which a gas
turns into liquid
1. At dew point air is saturated
2. Ice in a glass of water causes air
surrounding glass to cool to dew point
3. Before water vapor can condense has to
have a surface to condense on, e.g. glass
IV. Clouds
1. Collection of millions of tiny water
droplets or ice crystals
2. Form as warm air rises and cools.
3. As rising air cools it becomes
saturated and then water vapor
changes to liquid or solid depending
on air temperature
4. If temperature above freezing, water
vapor condenses on small particles in air
forming tiny water droplets.
5. If temperature below freezing, water vapor
changes to solid to form ice crystals.
6. Clouds classified by form
A. Cumulus Clouds
1. Puffy, white clouds, have flat
bottoms.
2. Form when warm air rises
3. Indicate fair weather
4. When clouds get bigger produce
thunderstorms
a. Thunderstorms come from
cumulonimbus clouds
b. Clouds with names ending in nimbus or
nimbo produce precipitation
B. Stratus Clouds
1. Form in layers
2. Cover large areas of the sky blocking sun
3. Can be caused by gentle lifting of a large
body of air into atmosphere.
4. Nimbostratus clouds are dark stratus
clouds usually produce light to heavy,
continuous rain.
5. Fog is a stratus cloud formed near the
ground
C. Cirrus Clouds
1. Thin, feathery, white clouds at high
altitudes
2. Form when wind is strong
3. If get thicker, indicates change in
weather
Clouds and Altitude
1.Clouds classified by altitude at which
they form.
a. Prefix cirro describes clouds that form at
high altitudes, example, cirrocumulus
cloud forms high in the atmosphere
b. Prefix alto – clouds that form at middle
altitudes
c. No prefix – clouds that form a low altitudes
V.
Precipitation
1. When water from air returns to Earth’s
surface, returns as precipitation
2. Can be solid or liquid
3. 4 major forms of precipitation are rain,
snow, sleet, and hail
A. Rain
1.Forms when water drops in clouds
become certain size
a. Starts as droplet, smaller than
period at end of sentence
b. Before water drop falls as rain must
be 100 times original size.
B. Sleet and Snow
1. Forms when rain falls through layer of
freezing air changing the rain to ice.
2. Snow forms when temperature so cold
that water vapor changes directly to a solid.
3. Snow can fall as single ice crystal or can
join to form snowflakes
C. Hail
1. Balls or lumps of ice that fall from
clouds.
a. Formed in cumulonimbus clouds
b. Updraft of air carries raindrops high in
clouds they freeze and hail forms
c. As hail falls water drops coat it.
d. Another updraft of air can send hail up
again, water drops collected on hail freeze
forming another layer of ice. Can happen
many times.
e. Eventually hail too heavy to be carried by
updrafts and falls to Earth’s surface
Chapter 16, Section 2
I. Air Masses and Fronts
A. Air Masses
1. Air Masses - large body of air where
temperature and moisture content
are similar throughout at any one
height.
a. Characterized by moisture
content and temperature
2. Form over parts of earth’s surface
called source regions.
a. Air mass over Gulf of
Mexico warm and wet
because area is warm and
has lots of water that
evaporates.
3. Many types of air masses, each
associated with particular source
region.
4. Types represented on maps by
two-letter symbol
a. (m) Maritime, forms over water,
wet;
b. (c) continental, forms over land;
dry
c. (P) Polar, forms over poles,
cold
d. (T) Tropical, forms over tropics;
warm
Air Masses & Fronts
Maritime Polar
mP
mT
Maritime Tropical
Maritime Polar
Continental Polar
cP
cT
Continental Tropical
Maritime Tropical
B. Cold Air Masses
1.Winter weather influenced by 3 polar
air masses
a. continental polar (cP) air mass
forms over northern Canada,
b. brings extremely cold winter
weather to U.S.
2. In summer cP air mass brings cool, dry
weather
3. Maritime polar (mP) forms over North
Pacific Ocean, cool and very wet
a. brings rain and snow to Pacific Coast in
winter and cool, foggy weather in
summer
4. Maritime polar air mass that forms over
North Atlantic Ocean brings cool, cloudy
weather and precipitation to New England
in winter. In summer it brings cool weather
and fog
C. Warm Air Masses
2. Warm front- when warm air meets
cool air
3. Warm air moves over cold air
4. Produces drizzles or warm weather
II. Fronts
A. Air masses forming from different areas often
don’t mix because they have different densities
called front
B. Cold Front
1. Forms where cold air moves under air,
which is less dense, pushes warm air up.
2. Move quickly and bring thunderstorms,
heavy rain, or snow
3. Cooler weather usually follows cold front
because air mass is cooler and drier than
air mass it replaces
C. Warm Front
1. Warm air moves over cold, denser
air
2. Warm air gradually replaces cold
air bringing drizzly rain followed
by clear, warm weather
E. Occluded Front
1. Forms when warm air mass is caught
between two cold air masses
2. Coldest air mass moves under and
pushes up war, air mass
3. Sometimes two colder air masses mix
4. occluded front has cool temperatures
and large amount of rain and snow
F. Stationary Front
1. Forms when cold air mass meets
warm air mass
2. May happen because not enough
wind to keep air masses against each
other.
3. Stationary front brings cloudy, wet
weather
No movement
Chapter 16, Section 3
I. Severe Weather
1. Can cause property damage and
death.
A. Thunderstorms
1. Small, intense weather systems
producing strong winds, heavy rains,
lightening, and thunder
2. Two atmospheric conditions required to
produce
a. Warm moist air near Earth’s surface
b. Unstable atmosphere
c. When surrounding air is colder than
rising air mass
d. Air mass continues to rise as long as
surrounding air colder than air mass
3. When rising warm air reaches dew point,
water vapor in air condenses and forms
cumulous clouds.
4. If air unstable warm air continues to rise
causing cloud to grow into dark
cumulonimbus cloud.
B. Lightning
1. Electric discharge that occurs between
positively charged area and negatively charged
area.
2. Can happen between 2 clouds
3. Between Earth and cloud
4. Even two parts of the same cloud
5. Ever touch someone after scuffing feet on
carpet and get shocked? That’s how lightning
forms.
a. Friction between floor and shoes builds up
electric charge in your body and when you
touch someone else charge is released.
6. When lightning strikes energy released,
transferred to air causing air to expand rapidly,
and sent out sound waves.
7. Thunder is the sound resulting from rapid
expansion of air along lightening strike
C. Severe Thunderstorms
1. Can produce high winds, hail, flash floods,
and tornadoes
2. Hailstorms damage crops, dent metal on
cars, break windows
3. Flash floods from heavy rain can cause
millions of dollars in property damage per
year
4. Every year flash flooding leading cause of
weather-related deaths
5. Lightning happens during all thunderstorms
very powerful
6. Starts thousands of forest fires and kills or
injures hundreds of people a year in U.S.
II. Tornadoes
1. Start with a thunderstorm, wind moves
from both directions and causes warm air to
get pushed up in the front
2. The cumulonimbus cloud begins to spin and
funnel
3. The funnel becomes a tornado when it
touches the ground
a. Happen only in 1% of all thunderstorms
III Hurricanes
1. Large, rotating tropical weather system
with wind speeds at least 120 km/h
2. Most powerful storms on Earth
3. Have different names in different parts of
world
4. Western Pacific Ocean called typhoons
5. Hurricanes forming over Indian Ocean are
cyclones
6. Most hurricanes form between the 50 and 200
north latitude and between 50 and 200 south
latitude over warm, tropical oceans.
7. At higher latitudes water too cold for
hurricanes to form
8. Vary in size from 160 to 1,500 km in diameter,
can travel thousands of km
A. How a Hurricane Forms
1. Begins as group of thunderstorms moving
over tropical ocean waters.
2. Winds traveling in two, or more different
directions meet and cause storm to rotate
3. Storm then turns counter-clock wise in
Northern Hemisphere and clock wise in
Southern Hemisphere
4. Gets its energy from condensation of water
vapor.
5. Once formed fueled through contact with
warm ocean water
6. Moisture added to warm air by evaporation
from ocean
7. As warm, moist air rises water vapor
condenses and releases large amount of
energy
8. Hurricane continues to grow as long as over
warm, moist air
9. When hurricane moves to colder waters or
over land begins to loose source of energy
IV. Safety of storms
A. Damage Caused by Hurricanes
1. Can cause lots of damage when move
near or onto land
2. Wind speeds of hurricanes range from
120 to 150 km/hour, can reach 300
km/hour.
3. Winds can knock down trees and telephone
poles, can destroy buildings and homes
4. Most hurricane damage caused by flooding from
heavy rain and storm surges
a. Storm surge is wall of water that builds up
over ocean because of strong winds and low
atmospheric pressure
5. Wall of water gets bigger as it nears shore and
greatest heights when it crashes onto shore.
6. Can surge 1 to 8 m high and 65 to 160 km long.
B. Thunderstorm Safety
1. Lightening most dangerous parts of
thunderstorm
2. Attracted to tall objects. If outside stay away
from trees, which can struck down
3. If in open area crouch down so you are not
tallest object in area.
4. Stay away from bodies of water, if lightning hits
water while in it you can be hurt or die
C. Tornado Safety
1. Weather forecasters use watches and warnings to let
people know about tornadoes
2. Watch is weather alert about tornado that may
happen
3. Warning is weather alert saying tornado has been
spotted
4. If tornado warning in area find shelter quickly, best
place basement, cellar, or windowless room in center
of building like bathroom, closet, or hallway. If outside
lie down in large, open field or deep ditch.
D. Hurricane Safety
1. TV or radio station keeps you updated on
condition
2. People living on shore may have to evacuate
3. If you live in area where hurricanes hit you
should have an emergency supply kit with
enough food and water for several days.
4. Cover windows with plywood
Chapter 16, Section 4
I. Forecasting the Weather
1. Weather forecast is prediction of
weather conditions over next 3-5 days
2. Meteorologist observes and collects
data on atmospheric conditions to make
weather predictions
A. Weather-Forecasting Technology
1. Meteorologists measure atmospheric
conditions like air pressure, humidity,
precipitation, temperature, wind speed, and
wind direction.
2. Use special instruments
B. High in the Sky
1. Weather balloons carry electronic
equipment that can measure temperature, air
pressure, relative humidity as high as 30 km
above Earth’s surface.
2. By tracking balloons meteorologists can
measure wind speed and direction
C. Measuring Air Temperature and Pressure
1. Thermometer
a. When air temperature increases,
liquid in thermometer expands and
moves up glass tube
b. As air temperature decreases liquid
shrinks and moves down tube
2. Barometer
a. Instrument to measure air pressure
b. Glass tube sealed at one end and
placed in container of mercury. As air
pressure pushes on mercury it moves
up glass tube.
c. Greater air pressure is, higher
mercury will rise
D. Measuring Wind Direction
1. Using windsock or wind vane
2. Windsock is cone-shaped, cloth bag,
open both ends
a. Wind enters through wide end
leaves through narrow end,
therefore, wide end points into
wind.
3. Wind vane shaped like arrow with large
tail and attached to pole.
a. As wind pushes tail of wind vane it
spins on pole until arrow points into
wind
E. Measuring Wind Speed
1. Anemometer
a. Has 3 or 4 cups connected by pokes to a
pole
b. Wind pushes on hollow sides of cups
causing cups to rotate on pole
c. Motion sends weak electric current that
is measured and displayed on a dial
F. Radar and Satellites
1. Radar used to find location, movement, and
amount of precipitation.
2. Can also detect form of precipitation weather
system is carrying
3. Doppler radar on TV weather reports shows
how Doppler radar used to track precipitation.
4. Weather satellites that orbit Earth provide
images or weather system seen on TV weather
reports.
5. Satellites track storms, measure wind speeds,
humidity, and temperatures at different altitudes.
II. Weather Maps
1. In U.S. National Weather Service (NWS) and
National Oceanic and Atmospheric
Administration (NOAA) collect and analyze
weather data.
2. NWS produces weather maps based on
information gathered from 1,000 weather
stations across the U.S.
3. On maps each station is represented by a
station model.
a. Station model is a small circle that shows
location of a weather station.
4. Surrounding small circle is set of symbols and
numbers representing weather data.
A. Reading Weather Map
1. On TV include lines called isobars that
connect points of equal air pressure
2. Isobars form closed circles representing
areas of high or low pressure
3. Usually marked on a map with capital H
or L
4. Fronts also labeled on weather maps.