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 How to
read the map:
Isobar Contour Lines As isobar contour lines come closer together wind speeds tend to increase. Cold Front  A cold front is the boundary between warm and cool air when the cool air is moving in to replace the warm air. In the northern hemisphere, winds ahead of the front will be southwest and shift into the northwest with frontal passage. A cold front is displayed as a blue line with triangles pointing in the direction the cold air is moving. Frontogenesis  This is a developing front.
Frontogenesis is any atmospheric process which leads to frontal formation,
or to an existing weak frontal zone becoming enhanced. On charts issued by
some national meteorological services, such fronts are shown with the
normally solid line defining the front broken by spaces and large dots.
Frontolysis
 This is a dissipating front.
The weakening or dissipation of a front occurs when two adjacent air
masses lose contrasting properties such as the density and temperature. It
is the opposite of frontogenesis.
Occluded
Front
 Occluded fronts can signal
the weakening of a storm. A cold occlusion, which occurs when the air
behind the front is colder than the air ahead of the front, acts similarly
to a cold front. A warm occlusion occurs when the air behind the front is
warmer than the air ahead of the front and acts similarly to a warm front.
Stationary
Front
 A stationary front is the
boundary between cool and warm air when the pushing is at a standoff.
Stationary fronts often bring several days of cloudy, wet weather that can
last a week or more. A stationary front is depicted as alternating blue
triangles pointing away from the cold air and red half circles pointing
away from the warm air.
Trough or
Trof
 Precipitation tends to fall
to the east of the trough axis while colder, drier air tends to prevail to
the west of the trough. A trough is an elongated area of relatively low
pressure typically associated with a cyclonic wind shift.
Warm Front
 A warm front is the boundary
between warm and cool, or cold, air when the warm air is replacing the
cold air. The warm front symbol on a weather map marks the boundary
between warm and cold air at the earth�s surface. The circles on the red
line point in the direction the warm air is moving. A slow-moving warm
front can mean hours or days of cloudy, wet weather before the warm air
finally arrives.
High
Pressure
 High pressure systems bring
sunny days with little or no precipitation. Air tends to sink near high
pressure centers, which inhibits precipitation and cloud formation. Air in
a high pressure area compresses and warms as it descends. The warming
inhibits the formation of clouds, meaning the sky is normally sunny in
high pressure areas.
Low Pressure
 Air rises near low pressure
areas. As air rises, it cools and often condenses into clouds and
precipitation. Low pressure systems have different intensities with some
producing a gentle rain while others produce hurricane force winds and a
massive deluge.
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