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Term 2---Weather Notes
term
definition or information
air pressure
 barometric pressure (millibars)
 weight of air pressing at a given location
****changes in air pressure are a sign that weather is about
to change (drops rapidly means a low pressure system is
approaching)
****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
 Freezing--- 0° Celsius; 32° Fahrenheit
 Boiling---- 100° Celsius; 212° Fahrenheit
humidity
anemometer
cold front
 amount of water vapor in the air (damp/sticky)
 Relative humidity--- compares water vapor in the air
(absolute humidity) to the water vapor that air can hold at
a given temperature
--- given as a percentage %
---affects the dew point
 Dew---water vapor that condenses on a surface
---formation depends on the air temp and amount of water
vapor in the air
---dew point--measure of the temperature at which more
water vapor will condense than will evaporate
 used to measure wind speed
 miles per hour (mph)
 cold air mass pushes under a warm air mass, forcing the
warm air to rise sharply
 heavy rain, thunderstorms, or snowstorms
 the temperature drops
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diagram or picture
barometer
Fahrenheit or Celsius
thermometers
hygrometer
Term 2---Weather Notes
warm front
 warm, moist air mass slides up and over a cold air mass
 warm fronts usually bring light rain and cloudy weather.
 the temperature rises
stationary
front
occluded
front
hurricane--(typhoons,
tropical
cyclones,
Willy
Willies)
 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
 rotating low-pressure system that forms over warm water
 wind speeds of at least 74 mph (category 1)
 rotate counterclockwise
 over warm water, moist air rises into it to give it energy
 trade winds in the Atlantic steer hurricanes westward
 Gulf Stream’s warm sea surface temps aid in the
formation and strengthening of the hurricanes that move
through the Gulf of Mexico
 Prediction cones---Scientists also use data from past
hurricanes to develop computer models that predict how a
new hurricane may behave.
****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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Term 2---Weather Notes
convection
 circular flow due to temp differences
current
 heat moves warmer to cooler
 continuous rising warm air and
sinking cool air
 warm air rises and cool air sinks due
to density
polar
easterlies


trade winds



westerlies


doldrums



Coriolis
effect


jet streams



cold, dense air moves away from
the high pressure areas around the
poles and curves west
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
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.
steer hurricanes westward in the
Atlantic
west to east and toward the poles
The westerly wind belt carries
storms across the United States.
located at equator
little to no wind
paths of winds and ocean currents
curve due to Earth’s rotation
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.
flows west to east
do not follow regular paths
around Earth
move north and south over
time
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Term 2---Weather Notes
Gulf Stream 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
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.
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
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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