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WINDS & PRESSURE ON SURFACE CHARTS




Pilots can gain a great deal of information from surface weather charts, which provide information about weather fronts, high- and low-pressure areas, surface winds and pressures.




Wind Speed and Direction

On these surface weather charts, winds that are reported by showing an arrow attached to a circle, which indicates a station. The station circle is the head of the arrow, the arrow points in the direction with wind is from.


The speed of the wind, which are represented by barbs or pennants on the arrow. Each barb or pennant represents a curtain speed in knots.




Isobars

Pressures are recorded on surface weather charts for each station in millibars (mb). Isobars are lines of pressure that are drawn on charts.

  • If the Isobar lines are closely spaced, that indicates a steep pressure and strong winds.

  • If the lines are spaced far apart, the winds are light.


Isobars also show high- and low-pressure systems, along with ridges, and troughs on charts.

  • A ridge is an elongated, upward curve of High pressure.

  • A trough is an elongated, downward curve of Low pressure.


Isobars give information about winds in the first few thousand feet above the surface. The wind direction is different from winds above and the speed is decreased, due to friction along the surface. At 2,000 to 3,000 feet in altitude, the winds speed up and the direction becomes parallel to the indicated isobars.

The wind at 2,000 feet AGL is from 20⁰ to 40⁰ to the right of surface winds. Wind direction is greater over rough surfaces, such as mountains, valleys, and canyons than over flat surface i.e., plains, fields, etc.

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