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How To Read A Weather Map

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How To Read A Weather Map - PowerPoint PPT Presentation

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How To Read A Weather Map. Geography Skills. Weather maps provide a simplified depiction of the current or predicted weather conditions of an area . Weather maps. Understand general concepts of the weather.

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Presentation Transcript
step 1

Understand general concepts of the weather.

    • 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.
Step 1
step 2

Find a weather map.

  • Watch out for one on the TV news, online, or in your local newspaper.
    • (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….
Step 2
step 3

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

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.
clear calm

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
step 4

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
f ronts

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.