Weather Analysis: Contouring AOS 101 Section 305

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Weather Analysis ContouringAOS 101 - Section 305

• Dan Hartung
• February 8, 2008

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Contouring

• Contoured maps of certain variables (like this,
  of temperatures at 850 mb) help to graphically
  show locations of strong fronts, low/high
  pressure systems, etc.

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How to think about contouring

• Think of contouring as a topographic map, where
  the lines represent places of constant height
  above sea level.
• If you were to walk along one of these lines, you
  would ALWAYS be at the same height above sea
  level.

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What else can be contoured?

• Isopleth a line on a map connecting points at
  which a given variable has a specified constant
  value
• Isobar A line of constant pressure
• Isotherm A line of constant temperature
• Isodrosotherm A line of constant dewpoint
• Isotach A line of constant wind speed
• Isohyet A line of constant precipitation
  accumulation
• Isoneph A line of constant cloudiness
• Isohaline A line of constant salinity
  (saltiness in the ocean)
• Isoheight A line of constant height

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Isobar Line of constant pressure
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Isotach Line of constant wind speed
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Isotherm Line of constant temperature
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Isohyet Line of constant precipitation
accumulation
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Isodrosotherm Line of constant dewpoint
http//www.rap.ucar.edu/weather/model/eta00hr_sfc_
dewp.gif
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Rules and Tips for Contouring

• Contours will never cross each other
• Contours never branch or fork, they are always
  one continuous line
• Do not create contours where there is no data
  (i.e., over the oceans)
• Always label your contours
• Contour at evenly spaced increments (for surface
  temperature, well do every 5 degrees Fahrenheit,
  and for sea level pressure, every 4 millibars)

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Rules and Tips for Contouring

• Use a pencil! You will be erasing
• Locate regions of high and low values first
• Initially, sketch out how you will be making
  your first few contours
• Make your lines as smooth as possible.
• Ignore outliers, data that doesnt seem like it
  fits with the big picture.
• If you need more help, try
• http//cimss.ssec.wisc.edu/wxwise/contour/contour1
  .html

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Examples

• Lets say we have the following set of temperature
  readings. Where should the 20º F isotherm be
  drawn?

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21
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Examples

• Lets say we have the following set of temperature
  readings. Where should the 20º F isotherm be
  drawn?

16
20
18
21
22
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Examples

• Lets say we have the following set of temperature
  readings. Where should the 75º F and 80º F
  isotherms be drawn?

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Examples

• Lets say we have the following set of temperature
  readings. Where should the 75º F and 80º F
  isotherms be drawn?

75
80
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Now for some more examples