Transcript weather powerpoint

•a large body of air that has the
same temperature and humidity
throughout
•classified according to where
they originate
•during the time the air mass is
over an area, it determines the
weather of that area
•Classified according to two
characteristics: temperature and
humidity.
•The maritime tropical, continental
tropical, maritime polar, and
continental polar influence the
weather in North America
maritime tropical
• humid air mass (m) Originates over the
ocean
• Form over the Gulf of Mexico and Atlantic
Ocean and move into the southeastern U.S.
• Form over the Pacific and affect the west
coast
• In summer they bring hot, humid weather
and in winter heavy rain or snow
Originates in warm air
warm air mass (T) (Tropical)
Maritime Polar  Cool, humid air
masses form over the icy cold North
Pacific and North Atlantic Oceans
• Affect west coast bringing fog, rain,
and cool temperatures
continental tropical  dry air mass (c)
Originates over the land
continental Polar cool air mass (P) Originates in
cold air
Form over central and northern Canada and
Alaska
In winter continental polar masses bring clear,
cold, dry air to much of North America
Storms occur with the CP collides with the MT
Maritime Tropical Atlantic (mT)
•moves northward across eastern
US
•brings mild, cloudy winters and hot
humid summers with hurricanes and
thunderstorms
How air masses move
• In the United States, air masses are
moved by:
• prevailing westerlies-pushes air
masses west to east
• jet stream-bands of
high speed winds 10km
above earth’s surface
that carry air masses
fronts: boundary between two
air masses having different
temperatures and humidity
•warm air overtakes cool air
•warm air rises
•brings hot, humid days and
precipitation over a large area
•cold air overtakes warm air
because it is more dense
•cold air forces warm air up
•Since warm air holds more moisture than
cool air, once the air reaches the dew
point heavy rain or snow will form.
•brings strong storms (squall) with clear,
cooler days once it passes
•two cold masses sandwich a warm
mass
•warm air rises between them
•brings strong winds and heavy
rains
•does not move
•These can bring many days of clouds and
precipitation until it moves.
Cyclones and Anticyclones
• Occur when boundaries between fronts get
distorted by physical features or jet streams and
air begins to swirl.
• Cyclone- (L) swirling center of low air pressure
• These play a large part of the weather in the
United States and winds spin counter clock wise
• Cyclones and decreased air pressure are
associated with clouds, wind, and precipitation
• Anticlone- (H) high pressure centers of dry air,
winds spin clockwise, these cause dry, clear
weather
3.2 Storms
• A violent disturbance in the atmosphere
•small-area storms formed by the
strong upward movement of warm,
moist, unstable air
•always accompanied by lightning,
thunder, and usually rain
• formed from cumulonimbus clouds
known as thunderheads
• Form on hot humid afternoons or
when air is forced upward along a cold
front.
• Warm, humid air rises rapidly, the air
cools forming dense thunderheads
Lightning:
•a discharge of electricity from a
thundercloud to the ground, or
cloud to cloud, or ground to cloud
•temperature inside lightning
flash can reach 30,000°C
•at this temperature, air
expands explosively-sudden
expansion makes thunder!
Thunderstorm damage
• Lightning can cause fires, shatter tree trunks
• Shock people, cause burns, and heart failure
• Areal flooding
Thunderstorm safety
• Remain indoors away from phones,
electrical appliances, and plumbing fixtures
which can conduct electricity.
• Avoid metal objects and bodies of water.
• If you are stuck outside find a low area
away from trees, poles, and fences and
crouch down.
a narrow, funnel-shaped column of
spiral winds that extends
downward from the cloud base and
touches the ground
•strongest winds between 360 and
500 km/hr
•funnel less than 500 m across
•always travel with a parent
thunderstorm at speeds ranging
from 40 to 65 km/hr
funnel is a mixture of clouds and dust
pressure gets lower in center
lowering of
condensation level due
to low pressure causes
cloud to funnel
air flows
toward the
funnel and
cools to dew
point- drops
form
Extremely low
pressure-when it
touches ground,
acts like a giant
vacuum
Tornado Alley
• 800 tornadoes occur in the US each year
• Tornadoes can occur everywhere in the
country but are most likely to occur in
tornado alley
Waterspout: tornados over the waterweaker than tornados
Usually occur in the spring and summer,
and most likely in the late afternoon.
• Tornadoes are ranked on the Fujita
scale by the amount of the danger
they cause.
• The scale goes from F0 to F5
Tropical depression: wind speeds
up to 38 mph; some circular
rotation at surface
Tropical storm: wind speeds from
39-74 mph; can be named, shows
drop in pressure, distinct rotation
an intense tropical lowpressure area with sustained
winds starting at 75 mph
How Hurricanes Form
• Form in the Atlantic, Pacific, and Indian Ocean.
• Forms in the Atlantic north of the equator in
August, September, or October
• It begins over warm ocean water as a low-pressure
area, or a tropical disturbance
• It draws energy for the warm, humid air at the
ocean’s surface
• Winds spiral inward toward the area of lowest
pressure at the center.
• The lower the air pressure at the center of a
storm the faster the winds blow toward the
center
Movement of Air in a Hurricane
How Hurricanes Form
• Winds are strongest in a narrow band
around the center of the storm.
• At the center is a ring of clouds called the
eyewall.
• Inside the eyewall is the “eye” which is
characterized by calm air and possible
clear skies
• After the eye passes the storm resumes in
the opposite direction
There are sometimes gaps in between these bands where no
rain is found. In fact, if one were to travel between the
outer edge of the hurricane to its center, one would
normally progress from light rain to dry back to slightly
more intense rain again over and over with each period of
rainfall being more intense and lasting longer until reaching
the eye. Upon exiting the eye and moving towards the edge
of the hurricane, one would see the same events as they did
going in, but in opposite order.
A schematic of this banding feature can be seen in the
diagram above. The thunderstorms are now organized into
regions of rising and sinking air. Most of the air is rising, but
there is a small amount found in between the thunderstorms
that is sinking.
eye: central area of sinking air; 15
to 20 km wide
•Winds most violent just outside
the eye
How Hurricanes Move
• Hurricanes that form in the Atlantic
are steered by easterly trade winds
toward the Caribbean islands and the
south eastern United States
• Once overland they gradually loose
strength.
storm surge: currents formed when
hurricanes pile water up along the shore
and blow it inland
most damaging part of a hurricane because
it can wash away beaches, destroy buildings
and erode coastlines.
3.3 Predicting Weather
• Meteorologists- scientists who study the
causes of weather and try to predict it
• Meteorologists interpret weather
information from:
• Satellites-orbit the earth in the exosphere
and take images of earth’s surface, clouds,
storms, and snow cover.
Meteorologists interpret weather
information from:
commercial
aircraft
weather balloons- stay in
the troposphere and lower
stratosphere. They
measure temperature, air
pressure, and humidity
Computer forecasts- instruments
gather large amounts of data
weather stations
around the world
Radar: electronic
device that transmits
radio waves in the form
of a beam
Data is collected and put into a
central computer at the National
Weather Service
•data includes: wind speed and
direction, temperature, pressure,
humidity, clouds, precipitation
•Makes a computer model (copy of
the atmosphere in computer
•Maps are made and forecasts are
reported to local stations across
the country
•Weather forecasts are issued by
the Weather Service at 10 am, 4
pm, 9pm, and 4 am. Forecasts are
updated more often during severe
weather.
watch: threat of storm
conditions within 24-36 hours
warning: due to strike within 24
hours
Reading Weather Maps
• Isobars – lines joining
places on the map that
have the same air
pressure
• Isotherms – lines
joining places on the
map that have the
same temperature
Weather Map Symbols
Newspaper Weather Maps