Download Front Maps

Front Maps
MAP:
http://www.weather.com/maps/maptype/currentweatherusnational/index_large.html
QUESTIONS:
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What is a low-pressure system?
What is a high-pressure system?
What kind of weather does each typically bring?
What is a cold front?
What is a warm front?
What is an occluded front?
What is a stationary front?
What type of weather does each type of front typically bring?
Explain how the map key shows each of the terms above.
What is a High Pressure System?
A high pressure system is a whirling mass of cool, dry air that generally brings fair weather and light
winds. When viewed from above, winds spiral out of a high-pressure center in a clockwise rotation in
the Northern Hemisphere. These bring sunny skies. A high pressure system is represented as a big,
blue H.
What is a Low Pressure System?
A low pressure system is a whirling mass of warm, moist air that generally brings stormy weather
with strong winds. When viewed from above, winds spiral into a low-pressure center in a
counterclockwise rotation in the Northern Hemisphere. A low pressure system is represented as a
big, red L.
What is an air mass?
An air mass is an extremely large body of air whose properties of temperature and moisture content
(humidity), at any given altitude, are fairly similar in any horizontal direction. Air masses can cover
large (hundreds of miles) areas. Air masses can control the weather for a relatively long time period:
from a period of days, to months. Most weather occurs along the periphery of these air masses at
boundaries called fronts. There are 4 general air mass classifications categorized according to the
source region: polar, tropical, continental and marine.
What is a front?
A front is a boundary between two different air masses, resulting in stormy weather. A front usually is
a line of separation between warm and cold air masses.
How do you identify a front on a surface weather map or by your own weather observations?
Look for: Sharp temperature changes over a relatively short distance, change in moisture content,
rapid shifts in wind direction, pressure changes, clouds and precipitation patterns.
What is a cold front?
A cold front is a boundary between two air masses, one cold and the other warm, moving so that the
colder air advances toward the warm air and undercuts it, pushing it up. This type of frontal system is
associated with the rapid ascent of the air, leading to heavy precipitation such as thunderstorms. A
cold front is represented as a blue line with the teeth pointing toward the direction of movement.
What is a warm front?
A warm front is a boundary between two air masses, one cool and the other warm, moving so that the
warmer air overruns the cooler air. This type of frontal system is associated with the gradual ascent of
the air, leading to steady precipitation. A warm front is represented as a red line with half circles
pointing toward the direction on movement.
When a warm front passes through, the air becomes noticeably warmer and more humid than it was
before. As the warm air rises over the cold air the water vapor in it condenses into clouds that can
produce rain, snow, or sleet. A slow-moving warm front can mean hours, if not days, of cloudy, wet
weather before the warm air finally arrives.
What is a stationary front?
When a warm or cold front stops moving, it
becomes a stationary front. Once this
boundary resumes its forward motion, it
once again becomes a warm front or cold
front. A stationary front is represented as
an alternating warm and cold front
symbols. The blue triangles point towards
the warmer air and the red semicircles
point towards the colder air. A wide variety
of weather can be found along a stationary
front, but usually clouds and prolonged
precipitation are found there. When there
is a lot of water vapor in the warmer air
mass, significant amounts of rain or
freezing rain can occur.
What is an occluded front?
When a cold and warm front merge into one front, it is known as an occluded front or occlusion. The
warm air mass becomes trapped between two colder air masses, one from the west and one from the
east, and is forced up. Occluded means “closed in.” This type of front has showery precipitation can be
severe. An occluded front is represented as a purple line with teeth and half circles.
What are ridges and troughs?
A trough on a weather map is an elongated area of relatively low pressure. Since air is rising, troughs
bring cloudy and rainy weather. A trough is represented by a hash mark line.
A ridge is an elongated area
of relatively high pressure
extending from the center of
a high-pressure region. Since
air is often sinking within a
ridge, they tend to bring
warmer and drier weather.