ISOBARSFamiliar idea, new focus !

Isolines

(review)

• An isoline is a line connecting points of equal value.

Examples of isolines:• Contour: – points of equal altitude

• Isotherms: – points of equal temperature

• Isobar:– points of equal barometric (air) pressure

• (The weather channel loves isolines!)

Rules for Drawing Isolines:

• 1. Isolines connect points of equal value.

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• 2. Isolines are gentle, curving lines- no sharp corners.

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• 3. Isolines are always closed curves even though the map might only show part of it.

• 4. Isolines NEVER cross- this would mean that one point has two different values.

Ex: one spot has two temperatures?

20°

30 °

40 ° 50 ° 60 °

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YZ

• 5. Isolines usually are parallel. (They have a parallel trend.)

Gradient• Gradient shows how quickly the value

changes from one point to another.

Gradientvalue

dis c e

tan

Our “VALUE” is air pressure, when talking about isoBARS

BARs BARometer air pressure

• A steep (high) gradient changes quickly and the isolines are close together.

• A gentle (low) gradient changes slowly and the lines are far apart.

Steep areaGentle area

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HL 996 mb

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Follow up questions:

1. Describe the wind motion in the H.

2. Describe the wind motion in the L.3. In what area is the wind speeds the

greatest?

4.Winds go from ___ to ____ for pressure.

Summary

• Winds around a High blow in a clockwise direction away from the center. (“The clock is high.”) Highs usually have fair weather.

• Winds around a Low blow in a counter-clockwise and inward. (“The counter is low.”) Low pressure systems often have stormy or unsettled weather.