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Essential Question:
Weather (Chapter 20)
Air Masses:
 a body of air in the lower troposphere that has similar characteristics
 temperature & humidity depends on where they form
 named for where they form
Characteristics:
Temperature

depends on if the air mass
originates in a polar, arctic or
tropical regions
5 Types of Air Masses:
Summary:
Humidity

depends on if the air mass
originates over a continent
(continental) or ocean
(maritime)
Essential Question:
1. Continental Arctic (cA)
 extremely extremely cold & dry
 originates in arctic regions – coldest temperatures
 NO precipitation
2. Continental Polar (cP)
 warmer than cA, but only a slight difference in temperature &
humidity
 creates some precipitation
 creates lake-effect snow around the Great Lakes
3. Maritime Polar (mP)
 originates over oceans in high latitude
 cold, damp air mass
 not as cold as cP because water is water than the land
 when mP cools to its dew point fog, clouds, and/or precipitation is
formed
4. Maritime Tropical (mT)
 originates over warm, tropical oceans
 warm, moist air
 thunderstorms likely to develop
5. Continental Tropical (cT)
 originates over deserts
 hot, dry air
 can exceed 100oF
 may originate as a maritime tropical but dries out over land
Fronts:
 boundaries between different air masses
 air masses do not easily mix
 frontal systems are the cause of weather in the mid-latitudes since this is
where air masses mix
 bring storms and precipitation
 types & severity of weather depend on the type of air mass and how fast
air masses are moving
Summary:
Essential Question:
Four kinds of Fronts:
1. Cold Fronts
 the boundary between an advancing cold air mass and the warm air
mass it is replacing
 cold air is more dense so it slides under
warm air and pushes it up
 Moves quickly so precipitation doesn’t last
long
 Steep slopes so band of precipitation on
ground isn’t wide
 type of weather depends on type of air it is replacing
2. Warm Fronts
 the boundary between an advancing warm air mass and the cold air
mass it is replacing
 warm air rises, cold air slowly retreats
(slowly pushed on)
 slope is more gradual than a cold front
 upper level clouds form first, then lower
level clouds weather changes are less dramatic
 thunderstorms uncommon, prolonged rain and flooding are very
common
Summary:
Essential Question:
Warm Front:
3. Stationary Front
 front that is not moving forward
 caused because the warm air is not
moving fast enough to push the cold air
away, the front stalls
 prolonged precipitation & flooding occur
Summary:
Essential Question:
4. Occluded Front
 cold front “catches up” to a warm front
 warm air is wedged above cold air
 weather varies, depending on the time of
year – usually big storms
Severe Weather:
 Thunderstorms
o storms with lightning, thunder, and hail
o warm, moist unstable air - cumulonimbus clouds
o usually occur in the afternoon or evening because the Earth has
been heating up all day
o convection within the cumulonimbus clouds gives the storm it’s
energy
o forms along low pressure systems and cold front boundaries
Summary:
Essential Question:
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
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Summary:
Squall Line
o line of severe thunderstorms that precede a cold front
o bring torrential rains, hail, tornadoes, and lightning
Lightning
o discharge of electricity from a thundercloud caused by friction
o Can occur within a
cloud, between clouds, or
cloud to ground
o positive charge on top
and bottom of cloud &
negative charge in the
middle
Tornadoes
o violently rotating column of air that usually touches the ground
o in order for a tornado to form, there must be a rotating updraft
called a mesocyclone
o when a tornado has not yet reached the ground it is called a funnel
cloud
o The Fujita Scale
 Measures the intensity of a tornadoes using wind speed and
damage
 also called the F-scale
Essential Question:
o Tornado Alley
 area of the USA
where tornadoes
are likely to form;
extends from
northern Texas to
North Dakota
 warming of the
ground and the
constant wind in
the region are ideal for mesocyclones to form
 place where warm, moist air from the Gulf of Mexico
meets and mixes with cooler, dry air from the west and
southwest

Storm/Tornado Watches & Warning


Summary:
WATCHES
conditions are favorable
for a storm or tornado

WARNINGS
a severe storm or tornado
has been seen and is
approaching
Hurricanes
o large rotating storms of tropical origin that have sustained winds of
at least 119 km/h
o last for 1+ days
o have low pressure centers that draws energy from warm oceans
o strongest winds and rain occur around the eye wall
o inside the eye, winds are mild with little to no rain
o air rises in the eye wall
o Formation of Hurricanes
 need warm, moist air for extended period of time
 June 1st –November 30th
 form between 5o – 20o N and S of the equator
 starts off as a tropical depression and evolve to tropical
storms
 weaken when they make landfall
Essential Question:


steered by global wind patterns
in the Atlantic
form off west coast of Africa and move
west towards North America
o The Saffir-Simpson Scale
 categorizes hurricanes based on their wind speed and storm
surge
 gives a general idea about impending damage
 hurricanes
change
categories
throughout
their life
Summary:
Essential Question:
o Hurricane Damage
 a storm surge is when strong eye wall winds blow ocean
water into a dome that makes landfall
 storm surge can raise the sea level several meters higher
than normal
o Hurricane Watches and Warnings
WATCH
WARNING
 a hurricane will arrive in
 a hurricane will arrive in
24-36 hours
less than 24 hours
 Winter Storms
o Snowstorms are storms with steady snowfall
o Blizzards are winter storms with heavy snow, winds and low
temperatures
o 3 criteria must be met for blizzards
 Winds over 56 kph
 Temperatures -7oC or lower
 Reduction of visibility as a result of falling or blowing
snow
Forecasting Weather
 Meteorologists collect data to create weather maps & station models
 Instruments Used
o Satellite images
o Radiosondes: instruments attached to balloons
o Weather stations
o Weather radar
o Airplanes
o Ships
Summary:
Essential Question:
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
Summary:
Information is organized into a station model to be put on a map
Station Models
o include temperature, dew point, cloud coverage, barometric
pressure, wind speed and direction
o international symbols so meteorologists around the world can read
them
Essential Question:
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




Summary:
Weather forecasts are based on computer models
Computers organize the data from many weather stations
Meteorologists draw in the fronts based on temperature, dew point, and
wind direction
Computers use mathematical equations to make forecasts over the next
days to few days
Meteorologists edit forecasts based on previous weather patterns for an
area and take into consideration urbanization.
Urbanization is the tendency for a city to be warmer than the surrounding
area based on the fact that buildings hold heat better than vegetation