Weather Analysis: Contouring AOS 101 Section 302

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Weather Analysis Contouring AOS
101 Section 302 Ross Lazear February 6, 2007
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Last week, we learned

• - Station models are an efficient and concise way
  to represent weather conditions at multiple
  locations
• How to plot and analyze these station models

- In the station model from MSN on Feb. 4 at
2029 UTC, to the right Temp -5 F Dewpoint
-22 F Sea Level Pressure 1022.6 hPa (mb) Wind
15 knots from the WNW Sky Missing, or obscured
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Last week, we learned
Station models do a good job of telling us what
the weather conditions are like over a large
area but at first glance, what are the lowest
and highest temperatures on this map?
http//ral.ucar.edu/weather
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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.
http//www.aos.wisc.edu
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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
http//www.spc.noaa.gov
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The winds are generally almost parallel to the
isobars. We call this geostrophy.
http//www.spc.noaa.gov
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Isotach Line of constant wind speed
http//www.aos.wisc.edu
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Isotherm Line of constant temperature
http//ral.ucar.edu/weather
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Isohyet Line of constant precipitation
accumulation
http//www.crh.noaa.gov/mkx/document/snow/images/s
now_12-11-00-rgn.gif
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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
Say these observations are temperatures. Where
should we draw the 15o F isotherm??
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Examples
Say these observations are temperatures. Where
should we draw the 15o F isotherm??
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Examples
Say these observations are temperatures. Where
should we draw the 75o F and 80o F isotherms??
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Examples
Say these observations are temperatures. Where
should we draw the 75o F and 80o F isotherms??
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Now, for some more examples...