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Weather Notes 2013-2014
term
definition or information
precipitation
 rain, sleet, hail, snow
 type of precipitation determined largely by air temp
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diagram or picture
rain
gauge
anemometer
 used to measure wind speed
 miles per hour (mph)
anemometer
wind vanes
 Used to measure wind direction
wind vane
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)
 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.
temperature
barometer
Fahrenheit or Celsius
thermometers
Weather Notes 2013-2014
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.
air mass
front
cold front
warm front
stationary
front
occluded
front
 a large volume of air with about the same temperature, air
pressure, and humidity throughout
 a boundary between two air masses
 High-pressure systems move into low-pressure systems at
fronts.
 most changes in weather occur at fronts
 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
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psychrometer
hygrometer
Weather Notes 2013-2014
hurricane-- large, rotating low-pressure system that forms over warm
Gulf of
tropical water
Mexico,
 wind speeds of at least 74 mph (category 1)
Atlantic,
 rotate counterclockwise
Caribbean,
 As long as a hurricane is over warm water, moist air rises
Eastern
into it and gives it energy.
Pacific
 can cause severe damage
Ocean
 use satellite photos to show the size and location
typhoons- Prediction cones---Scientists also use data from past
Northwest
hurricanes to develop computer models that predict how a
Pacific
new hurricane may behave. These predictions can save
Ocean
lives by warning people to move out of a hurricane’s
path.
tropical
 **With hurricanes, an increase in air pressure causes the
cyclones--hurricane’s wind speed to decrease (weaken). When the
Australia and
pressure decreases (lowers), the hurricane’s wind speed
Indian Ocean
increases (intensifies).
Weather Data Technology-weather satellites  orbit Earth
 providing images of the movement
of clouds, storms, water vapor, air
masses
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Weather Notes 2013-2014
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
Climate Zones--- temperature and precipitation are key factors
tropical zone
 closest to equator
 tend to be warm to hot yearround
 receive direct sunlight
throughout year
polar zones
 farthest from equator
 near Earth’s North and South
Poles
 least direct sunlight
throughout year
 tend to be cool to cold yearround
temperate zones
 located between polar and
tropical
 angle at which the sun’s rays
strike these regions changes
greatly throughout the year
 distinct seasons with very
different temperatures
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Weather Notes 2013-2014
convection current
 circular flow of gas or liquid
caused by temperature
differences
 heat moves warmer to cooler
 continuous movement of
rising warm air and sinking
cool air
 sun sets currents in motion by
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.
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
polar easterlies
 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.
trade winds
 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 2013-2014
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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