Transcript Reading Weather Maps

READING WEATHER MAPS
Understanding the red and blue lines
And what are those H’s and L’s?
WEATHER FRONTS
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The boundaries between air masses
A front is defined as the transition zone between two
air masses of different density
Weather can change quickly, and it is due to the
movement of air masses in the atmosphere. An air
mass is a large chunk of air ... often many tens of
miles wide ... that shares the same temperature and
humidity.
When two different air masses meet, the boundary
between them is called a front, and bad weather is
usually the result
STATIONARY FRONT
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A front that is not moving (it is stationary)
When a warm or cold front stops moving, it
becomes a stationary 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.
THE WEATHER PULLS INTO THE STATION
FOR A BREAK
Stationary fronts occur when neither warm nor
cold air advances. The two air masses reach a
stalemate.
 That is what stationary means - that neither
front is moving.
 These type of conditions can last for days
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COLD FRONT
Transition zone from warm air to cold air
 A cold front happens when a fast-moving mass of
cold air hits a warm air mass. The warm air,
which holds a lot of water vapor, gets pushed
upward quickly
 A cold front is defined as the transition zone
where a cold air mass is replacing a warmer air
mass.
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BURR…IT’S A COLD FRONT
Cold fronts generally
move from northwest
to southeast.
 The air behind a cold
front is noticeably
colder and drier than
the air ahead of it.
 When a cold front
passes through,
temperatures can
drop more than 15
degrees within the
first hour.
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WARM FRONT
Transition zone from cold air to warm air
 A warm front happens when a fast moving mass
of warm air encounters a cold air mass, and rides
up on top of it.
 A warm front is defined as the transition zone
where a warm air mass is replacing a cold air
mass.
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IT’S GETTIN’ HOT IN HERE…WARM
FRONTS
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Warm fronts generally
move from southwest to
northeast and the air
behind a warm front is
warmer and more moist
than the air ahead of it.
When a warm front
passes through, the air
becomes noticeably
warmer and more
humid than it was
before.
OCCLUDED FRONT
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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.
HIGH AIR PRESSURE
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Rising air pressure means good weather is
coming
If you are experiencing high pressure, it means
that the air above you is falling, and
compressing. As this air falls, it gets warmer.
This means it can hold more water vapor, so any
clouds that exist will evaporate, leaving a clear
sky.
High pressure = “air is heavy” = dry, sunny
weather
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Dropping air pressure means that bad weather is
on the way
When you are experiencing low pressure, it
usually means that air above you is rising, and
expanding. This rising, expanding air will cool,
forcing its water vapor to condense, clouds to
form, and maybe rain to fall.
Low Pressure = “air is lighter” = unstable
weather