Lines, triangles and half-circles
How Do You Read a Weather Map?
Every symbol on a weather map says one thing: which way the air is going.
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Step 1 of 5
The curved lines are pressure contours.
Everything else on the map is decoration around these lines. Every point on one line has the same air pressure, exactly like the height contours on a hill map. They never cross.
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Step 2 of 5
Close lines mean strong wind.
Forecasters read wind speed straight off this spacing, without a number on the map Air flows from high pressure toward low. Where the contours crowd together the change is steep over a short distance, and the wind is fierce.
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Step 3 of 5
Highs are dry, lows are wet.
In a high, air sinks — warming, drying, clearing the sky. In a low, air rises, cools and makes cloud. That is the whole forecast in one word.
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Step 4 of 5
Fronts are where two air masses meet.
A front is the boundary between warm and cold air. Triangles mean cold air advancing; half-circles mean warm air advancing.
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Step 5 of 5
Fronts move, so the map is a film not a photograph.
Systems usually travel at thirty to fifty kilometres an hour. Knowing which way the fronts are heading turns today's chart into tomorrow's forecast.
The units are hectopascals; around 1013 is average, below 980 is a serious storm, above 1030 is a settled spell.
The short version
Weather map lines join equal pressures: crowded lines mean wind, highs mean settled air, lows mean rain, and fronts mark collisions.
Try it yourself
Find today's pressure chart online and note where the lines are closest. That is where today's strongest winds are.