Download How To Read A Weather Map

How To Read A
Weather Map
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Geography Skills
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Weather maps provide a
simplified depiction of the
current or predicted weather
conditions of an area.
Weather maps
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Understand general concepts of the weather.
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Step 1
What most people are concerned with is
precipitation, which, in meteorology (the study
of weather), is any form of water that falls onto
the Earth's surface.
Forms of precipitation include rain, hail, snow,
and sleet.
Generally, high pressure implies fair weather and
low pressure is usually associated with
precipitation.
Find a weather map.
 Watch out for one on the TV news, online,
or in your local newspaper.
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(Other sources may include magazines and
books, but they may not be current.)
 Newspapers are a convenient method to find a
weather map, as it is cheap, reliable, and can be
cut apart so that you can carry it with you while
learning to interpret the symbols.
 Or if you have a really nice teacher they will
provide you with one….
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Step 2
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Read the air pressure.
This is the weight or pressure the air exerts on the ground and is measured
in millibars.
It’s important to be able to read air pressure because pressure systems are
associated with certain weather patterns.
To read air pressure, check for isobars (iso = equal, bar = pressure) – plain,
curved lines that indicate areas of equal air pressure. Isobars play a major
role in determining the speed and direction of wind.
When the isobars form concentric closed (but not always round) circles, the
smallest circle in the center indicates a pressure center.
This can be either a high pressure system (depicted by an "H”) or a low
pressure system (depicted by an "L”).
Air does not flow "down" pressure gradients; it flows "around" them due to
the Coriolis effect (Earth spinning). Hence, wind direction is indicated by
the isobars, counterclockwise around lows (cyclonic flow) and clockwise
around highs (anticyclonic) in the northern hemisphere, thus creating
wind. The closer the isobars are to one another, the stronger the winds
Step 3
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Low Pressure System (Cyclone):
Increased cloudiness, winds, temperatures, and chance of
precipitation (rain).
Represented on a weather map by isobars that are very close
together, arrows traveling clockwise (Southern Hemisphere) or
counter-clockwise (Northern Hemisphere), usually with a "T" in
the middle isobar, which forms a round circle).
Tropical cyclones (South Pacific & Australia) are also named
hurricanes around America or typhoons in coastal Asia.
Cyclones
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High Pressure System:
Indicates clear, calm conditions with reduced chance of
precipitation (rain).
Drier air usually results in a greater range of high and low
temperatures.
Represented on a weather map as isobars with an "H" in
the middle isobar and arrows showing which direction the
wind is flowing (clockwise in Northern Hemisphere,
counter-clockwise in the Southern Hemisphere).
Clear & Calm
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Observe the types and movement of fronts.
These mark the boundary between warmer air on one side
and colder air on the other.
If you are close to a front and you know the front is
moving towards you, you can expect a change in weather
(e.g. cloud formation, precipitation, thunderstorms, and
wind) when the front boundary passes over you.
Its path can be distorted by mountains and large bodies of
water.
On a weather map, you will notice some lines that have
semi-circles or triangles on either side, or both (shown
here). These indicate the boundaries for various types of
fronts:
Step 4
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Cold front: Rainfall can be torrential and wind speeds
can be high. Represented on a weather map as a (blue)
line with triangles bordering one side. The direction that
the triangles point is the direction in which the cold
front is moving.
Warm front: Often brings a gradual increase in rainfall
as the front approaches, followed by prompt clearing
and warming after the front passes. If the warm air mass
is unstable, the weather might be characterized by
prolonged thunderstorms. Represented on a weather
map by (red) lines with semi-circles on one side. The
side that the semi-circles are on represent the direction
in which the warm front is heading.
Fronts