Lesson 1 Introduction
Lesson 2
Station Plotting-Decoding and Cloud Types
Lesson 3
Contouring I
Lesson 4
Contouring II
Lesson 5
Air Masses
Lesson 6
Fronts
Lesson 7
Satellite
Lesson 8
Radar and Thunderstorms
Lesson 9
Upper Air
Lesson 10
Mid-Latitude Cyclone
Lesson 11
Case Study I
Lesson 12
Case Study II

Contouring I

Background Material

This week you will begin the process of drawing isolines on maps. You may have seen similar lines on topographic maps indicating changes in height. These isolines are a very useful way to look at meteorological data; it allows us to ‘see’ the numerical data in more of a picture-like way--It can be easier to look at lines and contours on a map rather than to try and picture what all those individual numbers on the station models mean.

Temperature is usually a bit easier than pressure to contour, so we will start with it. Below you will find a list of contouring "rules". These rules apply to any line that you contour, whether it be temperature, pressure, etc., so remember them every time you contour ! After these exercises you will be able to look at a contoured map and obtain important meteorlogical information by examining the contours. Good isolines take time, however, so please practice practice!

 

There are 4 basic types of isolines:

Isotherms-- a line of constant temperature.

Isobar-- a line of constant barometric pressure.

Isohypse/Isopleth-- used mostly on upper level charts, is a line of constant geopotential height above the surface.

Isodrosotherm-- a line of constant dewpoint temperature.

 

Some general rules to follow in ALL contouring:

 

  • All data points along an isoline have the same value.
  • The interval between isolines is a constant value on any one map. Usually this interval is given (ex: 10° F), but may be implied.(ex: 4 mb)
  • You will be asked to choose your intervals by ‘centering’ on a value; (For example, center on 0° F and go up and down in 10° F intervals)
  • Lower values are always on one side of an isoline while higher values are on the other side of the line-Remember which is which as you go
  • Isolines NEVER CROSS OR TOUCH, NEVER SPLIT
  • Isolines will generally be SMOOTH AND PARALLEL
  • Interpolate between points as exactly as possible!
  • Do NOT draw lines where there are no data points. (You cannot interpolate where you have no data to go between!)
  • LABEL each isoline on the ends for open and in the center for closed isolines.

 

Isolines must be drawn to separate or include all data points.

 

Some hints:

Isotherms tend to run parallel to one another;

You will NOT typically see closed contours on a temperature contour map, except in mountains and desert regions where temps are more extreme-

 

Isobars tend to contour like circles around low and high pressure areas;

They might remind you of topographic maps with hills and valleys on them.

Return to Contouring I lesson.

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This web based lab section is being developed with assistance from the College of Letters and Science and the Cooperative Institute of Meteorological Satellite Studies.   Material presented is Copyrighted (C) 1999 by Steve Ackerman .  Feel free to use this material for non-profit educational purposes!