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The Weather Test Review
Air masses and fronts
–
Four types of air masses
in N. America (Maritime
means wet because the
clouds formed over the
ocean, continental means
dry because the clouds
formed over land, polar is
cold and tropical is hot)
• Maritime tropical
• Continental tropical
• Maritime polar
•
Continental polar
Warm Fronts
•
•
Warm front-Front
bringing warm air
Warm front - when a
warm moist air mass
rises above a cold air
mass, a warm front
forms. The gradient of
the front is very
shallow. Warm fronts
occur at the forward
edge of a depression (a
low-pressure system).
Cold Fronts
•
•
Cold front-Front moving into
an area bringing cold air
(Cold air moves under warm
air because it is more dense)
Cold front - a cold front
marks the advance of colder
air undercutting warm air.
The gradient of the cold front
is steeper than that of a
warm front, and the rainfall
is usually heavier.
Thunderstorms sometimes
form along a cold front.
Stationary front
• A transition zone between two
nearly stationary air masses of
different density. When a
warm or cold front stops
moving, it becomes a
stationary front. Once this
boundary resumes its forward
motion, it once again becomes
a warm front or cold front. A
stationary front is represented
by alternating blue and red
lines with blue triangles
pointing towards the warmer
air and red semicircles pointing
towards the colder air.
Occluded front
• when a cold front overtakes a
warm front
• A developing cyclone typically
has a preceding warm front
(the leading edge of a warm
moist air mass) and a faster
moving cold front (the leading
edge of a colder drier air mass
wrapping around the storm).
North of the warm front is a
mass of cooler air that was in
place before the storm even
entered the region.
Bad Weather-Cyclone
•
Cyclones and decreasing air
pressure are associated with
storms and precipitation In
low pressure areas as air
rises it cools. As the air
cools, the humidity in it
begins to condense into tiny
drops of water, or if it's cold
enough, into tiny ice
crystals. If there is enough
water, or ice, rain or snow
begin to fall. This is why low
pressure is associated with
bad weather.
Good Weather- Anticyclone
• The pressure is high at the
surface where air is slowly
descending
• much too slowly to feel. And,
this is going on over a large
area, maybe a few hundred
square miles.
• As air descends, it warms,
which inhibits the formation of
clouds.
• This is why high pressure is
generally - but not quite
always - associated with good
weather.
Storms
• Thunderstorms and
tornadoes form within
large cumulonimbus
(black and puffy)
clouds usually in low
pressure areas
Storm Safety
• During
thunderstorms avoid
touching metal
objects
Hurricanes
• A hurricane begins
•
•
over warm water in
a low pressure area
Hurricanes need
wind speeds of at
least 119 Kilometers
per hour
The eye of a
hurricane is calm
Snow
•
•
•
•
Snow falls when humid
air-cools below 0C.
If you are caught in a
snowstorm, try to find
shelter from the wind.
Lake effect snow is
caused by cold air
blowing over large lakes
then over land
Be sure to wear
sunglasses the snow
causes glare
Tornado
• A Tornado is a
•
•
funnel-shaped cloud
that touches the
surface of the earth
About 800 tornados
occur in the United
States each year
During a tornado a
basement is the
safest place to be
Floods
•
Floods occur when so
much water pours into a
stream or river that it
overflows its banks on
either side of the
channel
• Move to higher ground
•
and stay away from
flood waters
Boil water from sources
that have been flooded
Predicting the Weather
• Meteorologists
interpret weather
information from
local weather
observers,
instruments carried
by balloons,
satellites and
weather stations
around the world
Changes in weather technology
• Gathering weather
data with satellites
and weather balloons
• Using computers to
make forecasts
El Nino
•
•
is a weather pattern that forms
in the tropical Pacific Ocean
Occurs every 2-7 years In the
tropical Pacific, trade winds
generally drive the surface
waters westward. The surface
water becomes progressively
warmer going westward
because of its longer exposure
to solar heating. El Niño is
observed when the easterly
trade winds weaken, allowing
warmer waters of the western
Pacific to migrate eastward and
eventually reach the South
American Coast (shown in
orange). The cool nutrient-rich
sea water normally found along
the coast of Peru is replaced by
warmer water depleted of
nutrients, resulting in a dramatic
reduction in marine fish and
plant life.
Local Winds (Sea and Land
Breezes)
Weather maps
•
•
•
Small lines at the end of
the shaft that
represents wind
direction indicates wind
speed
Places with the same
temperature are
connected by isotherms
Isobars are areas with
the same air pressure