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A capital H or L at the middle of a set of closed isobars.
Also known as: H and L on a weather map
Two letters that determine most of what the weather will do. A low brings converging, rising air and so cloud and rain; a high brings sinking air and so settled conditions — and the rotation reverses between hemispheres.
A capital H or L placed at the centre of a set of closed isobars, marking the point of highest or lowest surface pressure, usually with the central value beside it.
Contexts: Maps
A low means converging air that must rise, cooling as it does, which produces cloud and precipitation. A high means sinking air, which warms and dries, producing settled weather. That is the whole of why the letters predict anything.
Air circulates anticlockwise round a low and clockwise round a high in the northern hemisphere, and the reverse in the southern, so the same symbol implies opposite wind directions depending on which half of a global chart it is on.
The rotation is hemispheric. The letter is not.
A large capital H or L at the centre of concentric closed curved lines, usually with a three- or four-digit number beside it.