Understanding Contouring in Meteorology: Rules and Techniques

1. Contouring AOS 101 Section 301 2 February 2009

2. Contouring • Rather than representing meteorological data as a set of separate points:

3. Contouring • It can be described as contours: lines of constant value

4. Contouring • It can be described as contours: lines of constant value (shaded)

5. Contouring • When contouring, we are assuming that the atmosphere is continuous – there are no sudden, abrupt changes over short distances

6. Contouring • In a continuous fluid like the atmosphere, when we see two different observations separated by some distance - 25 30

7. Contouring • - we assume that values in the intermediate space between those observations will progress from one observation to the other: 26 25 27 28 29 30

8. Rules of Contour Analysis 1) Contours do not abruptly begin or end in the middle of the plot: 25

9. Rules of Contour Analysis 1) Contours do not abruptly begin or end in the middle of the plot: 25

10. Rules of Contour Analysis 1) You can backtrack, loop around, and make closed loops in the plot 25 25

11. Rules of Contour Analysis 2) Lines cannot cross each other: 30 25

12. Rules of Contour Analysis 2) Lines cannot cross each other: 30 25 =/= 30 25

13. Rules of Contour Analysis 2) You can have multiple contours of the same value on the same plot: 30 25 30

14. Rules of Contour Analysis 2) You can have multiple contours of the same value on the same plot: 30 25 30

15. Rules of Contour Analysis 3) Contours do not branch or fork from one another; they are a single, continuous line or loop: 25

16. Rules of Contour Analysis 3) Contours do not branch or fork from one another; they are a single, continuous line or loop: 25

17. Rules of Contour Analysis 3) Contours do not branch or fork from one another; they are a single, continuous line or loop: 25

18. Rules of Contour Analysis 3) Again, use of multiple contours and closed loops can help you avoid these problems: 25 25

19. Rules of Contour Analysis 3) Again, use of multiple contours and closed loops can help you avoid these problems: 25 25

20. Rules of Contour Analysis 4) Always label your contours 5) Contour at evenly-spaced intervals 6) Do not allow contours to stray into regions where there is absolutely no data (e.g. oceans)

21. Helpful Hint • Think about the contour as a line separating the observations with higher values on one side of the line, and lower values on the other side:

22. Helpful Hint • Think about the contour as a line separating the observations with higher values on one side of the line, and lower values on the other side: 19 17 19 22 Draw the 25-line: 24 20 30 21 21 27 25 23 24 29 29 30 30 24

23. Helpful Hint • Think about the contour as a line separating the observations with higher values on one side of the line, and lower values on the other side: 19 17 19 22 Draw the 25-line: 24 20 30 21 21 27 25 23 24 29 29 30 30 24

24. Helpful Hint • Think about the contour as a line separating the observations with higher values on one side of the line, and lower values on the other side: 19 17 19 22 Draw the 25-line: 24 20 30 21 21 27 25 23 24 29 29 30 30 24 25

25. Helpful Hint • Think about the contour as a line separating the observations with higher values on one side of the line, and lower values on the other side: 19 17 19 22 Draw the 30-line: 24 20 30 21 21 27 25 23 24 29 29 30 30 24 25

26. Helpful Hint • Think about the contour as a line separating the observations with higher values on one side of the line, and lower values on the other side: 19 17 19 22 Draw the 30-line: 24 20 30 21 21 27 25 23 24 29 29 30 30 24 25

27. Helpful Hint • Think about the contour as a line separating the observations with higher values on one side of the line, and lower values on the other side: 19 17 19 22 Draw the 30-line: 24 20 30 21 21 27 25 23 24 29 29 30 30 24 25 30

28. Helpful Hint • Think about the contour as a line separating the observations with higher values on one side of the line, and lower values on the other side: 19 17 19 22 Draw the 20-line: 24 20 30 21 21 27 25 23 24 29 29 30 30 24 25 30

29. Helpful Hint • Think about the contour as a line separating the observations with higher values on one side of the line, and lower values on the other side: 19 17 19 22 Draw the 20-line: 24 20 30 21 21 27 25 23 24 29 29 30 30 24 25 30

30. Helpful Hint • Think about the contour as a line separating the observations with higher values on one side of the line, and lower values on the other side: 19 17 19 22 Draw the 20-line: 24 20 30 21 21 20 27 25 23 24 29 29 30 30 24 25 30

31. Commonly Seen Contour Plots • Here are some commonly seen contoured variables, and their names:

32. Sea-Level Pressure (Isobars)

33. Temperature (Isotherms)

34. Wind Speed (Isotachs)

35. Want Some Practice? • Professor Steve Ackerman has developed a website which allows you to practice contour analysis through a Java-applet: http://profhorn.meteor.wisc.edu/wxwise/contour/contour1.html

36. Your Homework • Using a plot of surface temperatures for the morning of January 24, 2009 (provided), create a contour analysis of surface temperature every 6 degrees divisible by 6 degrees (e.g. -12, -6, 0, 6, 12, etc.) • Suggestion: Start with the zero-line, then do positive values in order (6, 12, 18, etc.), then do negative values in order (-6, -12, -18, etc.)

38. -12? -4?