Weather Notes 2014-2015
term
definition or information
air pressure
 barometric pressure (millibars)
 weight of air pressing at a given location
 varies mostly due to the sun heats Earth’s surface
unevenly
 ****changes in air pressure are a sign that weather is
about to change (drops rapidly means a low pressure
system is approaching)
 Air over a heated surface absorbs heat from the surface,
expands, and becomes less dense. As the air’s density
decreases, air pressure also decreases.
 **With hurricanes, an increase in air pressure causes the
hurricane’s wind speed to decrease (weakens). When the
pressure decreases (lowers), the hurricane’s wind speed
increases (intensifies).
 Tornado----air pressure drops quickly; wind blowing in
opposite directions
 Low-pressure system-----usually bring cloudy, rainy, or snowy weather
---develops when an air mass at the Earth’s surface rises
(vacuum cleaner)
 High-pressure system-----sunny, fair weather, clear skies, calm conditions
---develops when an air mass sinks toward the ground
(hair dryer)
temperature
 determines how much water vapor the air can hold
 Warm air can hold more water vapor than cold air.
 Water evaporates faster at higher temperatures.
 On hot days more water evaporates and stays in the air.
 As warm, wet air cools, the water vapor may condense,
form clouds, and fall as rain.
 Freezing--- 0° Celsius; 32° Fahrenheit
 Boiling---- 100° Celsius; 212° Fahrenheit
humidity
 amount of water vapor in the air (damp/sticky)
 Relative humidity--- compares the amount of water vapor
in the air (absolute humidity) to the amount of water vapor
that air can hold at a given temperature.
--- given as a percentage %
--- measured using hygrometers
--- one common type is the psychrometer which
consists of two thermometers
---affects the dew point
 Dew---water vapor that condenses on a surface
---Dew formation depends on the air temperature and the
amount of water vapor in the air.
---The dew point is a measure of the temperature at which
more water vapor will condense onto a surface than will
evaporate from it.
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diagram or picture
barometer
Fahrenheit or Celsius
thermometers
psychrometer
hygrometer
Weather Notes 2014-2015
anemometer
 used to measure wind speed
 miles per hour (mph)
cold front
warm front
stationary
front
occluded
front
hurricane--Gulf of
Mexico,
Atlantic,
Caribbean,
Eastern
Pacific
Ocean
typhoons-Northwest
Pacific
Ocean
tropical
cyclones--Australia and
Indian Ocean
Willy
Willies--Australia
 cold air mass pushes under a warm air mass, forcing the
warm air to rise sharply
 Because the air rises quickly, tall clouds often form.
 Heavy rain, thunderstorms, and snowstorms occur at cold
fronts.
 When the cold front passes, the temperature drops and the
weather clears.
 warm, moist air mass slides up and over a cold air mass
 Since moist air is rising at a warm front, clouds usually
form.
 Warm fronts usually bring light rain and cloudy weather.
 After a warm front passes, the temperature rises and the
weather clears.
 two air masses meet and stop moving
 neither has enough force to lift the warm air mass over the
cold air mass
 brings light winds and wet weather, which can last for
several days
 forms when a warm air mass is caught between two colder
air masses, one of which overtakes the other
 The warm air is forced to rise.
 if an occluded front is accompanied by strong winds and
cooler temperatures, it can bring heavy rain or snow
 large, rotating low-pressure system that forms over warm
tropical water
 wind speeds of at least 74 mph (category 1) which can be
measured using anemometers
 rotate counterclockwise
 As long as a hurricane is over warm water, moist air rises
into it and gives it energy.
 can cause severe damage
 use satellite photos to show the size and location
 Prediction cones---Scientists also use data from past
hurricanes to develop computer models that predict how a
new hurricane may behave. These predictions can save
lives by warning people to move out of a hurricane’s
path.
 **With hurricanes, an increase in air pressure causes the
hurricane’s wind speed to decrease (weaken). When the
pressure decreases (lowers), the hurricane’s wind speed
increases (intensifies).
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Weather Notes 2014-2015
Weather Data Technology-weather satellites  orbit Earth
 providing images of the movement
of clouds, storms, water vapor, air
masses
Doppler radar
 radio/microwave
 located on Earth’s surface gather
data by sending out radio signals
that are reflected off objects such
as raindrops, snowflakes,
hailstones, or clouds
 detects the type and amount of
precipitation, location, height, and
movement of clouds
government
agencies
 NOAA ---National Oceanic and
Atmospheric Association
 NWS--- National Weather Service
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Weather Notes 2014-2015
Global winds--- by the heating of the sun and spinning of Earth; steers weather; solar energy absorbed near
equator warms air forming large areas of low pressure; warm air rises as the colder air near the poles sinks
forming high pressure areas
convection
 circular flow of gas or liquid caused
current
by temp differences
 heat moves warmer to cooler
 continuous rising warm air and
sinking cool air
 sun heating Earth’s surface unevenly
(more heat near equator)
 When air gets warmer, the molecules
move faster and spread farther apart.
 causes sea and land breezes
 Higher, cooler air sinks since it is
denser than warm air
 After it sinks, the cooler air is warmed
by the hot sand, becomes less dense
and rises.
polar
easterlies



trade winds

cold, dense air moves away from the
high pressure areas around the poles
and curves west
extend from the poles to 60° latitude.
In the Northern Hemisphere, the
polar easterlies bring cold arctic air
down over the United States. This
arctic air brings snow and freezing
weather.
warm, rising air at the equator
moves away from the equator
 Winds that blow toward the equator
from 30° latitude
 Cooler air north and south of the
equator moves toward the low
pressure area at the equator. This
cooler air makes up the trade winds.
 Coriolis effect causes these winds to
curve.
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Weather Notes 2014-2015
westerlies
 winds that flow from west to east
and toward the poles
 between the polar easterlies and the
trade winds
 found between latitudes of 30° and
60°
 The westerly wind belt carries
storms across the United States.
doldrums
 located at equator
 little to no wind
Coriolis
effect

jet streams

Gulf Stream
paths of winds and ocean currents
curve due to Earth’s rotation
 rotation or spinning of Earth on its axis
plays a role in wind patterns
 weather tends to move in curving,
circular patterns
 In the Northern Hemisphere, winds
moving north curve to the east and
winds moving south curve to the
west.
 Weather forecasters need to know this
to predict where winds and air
masses are likely to go.
 At every 30° latitude, the Coriolis
effect causes winds to curve in a different
direction.
high in the atmosphere, flowing from
thousands of kilometers from west to
east
 do not follow regular paths
around Earth
 move north and south over
time
Gulf Stream’s warm sea surface temps aid
in the formation and strengthening of
many of the hurricanes that move through
the Gulf of Mexico
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Weather Notes 2014-2015
Earth’s Seasons----revolution movement of Earth around the sun in its
orbit (one year)
rotation
 Earth takes 24 hours to complete one
rotation (one day)
 Earth spins on its axis (an imaginary
line that runs through the center from
one pole to the other pole)
tilt




solstice


equinox



Earth’s axis is tilted 23.5°
gives us the four seasons due to tilt and
location in revolution
Earth’s axis tilts different parts of Earth
toward or away from the sun at
different points in Earth’s orbit.
When the Northern Hemisphere is
tilted toward the sun, the Southern
Hemisphere is tilted away from the
sun. It is summer in the hemisphere
titled toward the sun. It is winter in the
hemisphere tilted away from the sun.
a point in Earth’s orbit when a
hemisphere is tilted as far as possible
toward or away from the sun
In the Northern Hemisphere---winter
solstice is Dec. 21 or 22; summer
solstice is June 20 or 21
a point in Earth’s orbit when the planet
is tilted neither toward nor away from
the sun
The vernal equinox or first day of
spring occurs in the Northern
Hemisphere on March 20 or 21.
The autumnal equinox or first day of
fall occurs in the Northern Hemisphere
on Sept. 22 or 23.
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