Transcript Contouring and Map Analysis

Contouring and Map Analysis
Lecture 2
February 1, 2010
Today’s Agenda
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Attendance
Weather Discussion sign-up
New material
In class activity
Contouring
• Station models do a good job of telling us
what the weather conditions are like over a
large area or at one station at one time…
• But contouring gives us even more
information
• Contoured maps give easy-to-read, general
information about small to large areas
• Contoured maps help in easily diagnosing
and depicting weather features and
variables
Contour analysis is vital in:
 Finding the location of atmospheric and
oceanic fronts.
 Locating regions with the potential of severe
weather
 Tracking storms, such as hurricanes and
blizzards
 Tracking the movement of pollutants
 A contour line is a line of a constant value or
an isopleth. Where iso means same
and pleth means value.
 A contour analysis involves drawing multiple
isopleths.
 Depending on what you are contouring, the
lines have different names
What can you contour?
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Isobar: A line of constant pressure
Isoheight: A line of constant height
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)
Isobars and Isoheights
Isotherms and Isoheights at 850mb
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, we’ll do every 5
degrees Fahrenheit, and for sea level
pressure, every 4 millibars)
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 doesn’t seem like
it fits with the “big picture.”
 If you need more help, try: tutorial on web
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:
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Draw the
25-line:
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30
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25
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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
Draw the
25-line:
17
19
22
24
20
21
30
21
27
25
23
24
24
29
30
29
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
Draw the
25-line:
17
19
22
24
20
21
23
30
21
27
25
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24 25
29
30
29
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Examples
 Say these
observations are
temperatures.
Where should
we draw the 15o
F isotherm??
Examples
 Say these
observations are
temperatures.
Where should
we draw the 15o
F isotherm??
Examples
Say these
observations are
temperatures.
Where should we
draw the 75oF
and 80oF
isotherms??
Examples
Say these
observations are
temperatures.
Where should we
draw the 75oF
and 80oF
isotherms??
Want extra 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
In Class Assignment
To convert from Z time to CST, subtract 6 hours. 05Z = 11 PM CST