Contouring and Map Analysis Lecture 2 February 1, 2010.

Contouring and Map AnalysisContouring and Map Analysis

Lecture 2Lecture 2

February 1, 2010February 1, 2010

Today’s AgendaToday’s Agenda

AttendanceAttendance Weather Discussion sign-upWeather Discussion sign-up New materialNew material In class activityIn class activity

ContouringContouring

• Station models do a good job of telling us Station models do a good job of telling us what the weather conditions are like over a what the weather conditions are like over a large area or at one station at one time…large area or at one station at one time…

• But contouring gives us even more But contouring gives us even more informationinformation

• Contoured maps give easy-to-read, general Contoured maps give easy-to-read, general information about small to large areasinformation about small to large areas

• Contoured maps help in easily diagnosing Contoured maps help in easily diagnosing and depicting weather features and variablesand depicting weather features and variables

Contour analysis is vital in:Contour analysis is vital in:

Finding the location of atmospheric and Finding the location of atmospheric and oceanic fronts.oceanic fronts.

Locating regions with the potential of severe Locating regions with the potential of severe weatherweather

Tracking storms, such as hurricanes and Tracking storms, such as hurricanes and blizzardsblizzards

Tracking the movement of pollutantsTracking the movement of pollutants

A contour line is a line of a constant value or A contour line is a line of a constant value or an an isoplethisopleth. Where . Where isoiso means same  means same and and plethpleth means value.  means value.

A contour analysis involves drawing multiple A contour analysis involves drawing multiple isopleths. isopleths.

Depending on what you are contouring, the Depending on what you are contouring, the lines have different nameslines have different names

What can you contour?What can you contour?

Isobar:Isobar: A line of constant pressureA line of constant pressure Isoheight:Isoheight: A line of constant heightA line of constant height Isotherm:Isotherm: A line of constant temperatureA line of constant temperature Isodrosotherm:Isodrosotherm: A line of constant dewpointA line of constant dewpoint Isotach:Isotach: A line of constant wind speedA line of constant wind speed Isohyet:Isohyet: A line of constant precipitation A line of constant precipitation

accumulationaccumulation Isoneph:Isoneph: A line of constant cloudinessA line of constant cloudiness Isohaline:Isohaline: A line of constant salinity (saltiness in A line of constant salinity (saltiness in

the ocean)the ocean)

Isobars and IsoheightsIsobars and Isoheights

Isotherms and Isoheights at 850mbIsotherms and Isoheights at 850mb

Rules and Tips for ContouringRules and Tips for Contouring Contours will Contours will nevernever cross each other cross each other Contours never branch or fork, they are Contours never branch or fork, they are

always always oneone continuous linecontinuous line Do not create contours where there is no Do not create contours where there is no

data (i.e., over the oceans)data (i.e., over the oceans) Always Always labellabel your contours your contours Contour at Contour at evenly spaced incrementsevenly spaced increments (for (for

surface temperature, we’ll do every 5 surface temperature, we’ll do every 5 degrees Fahrenheit, and for sea level degrees Fahrenheit, and for sea level pressure, every 4 millibars)pressure, every 4 millibars)

Rules and Tips for ContouringRules and Tips for Contouring

Use a pencil! You will be erasing…Use a pencil! You will be erasing… Locate regions of high and low values firstLocate regions of high and low values first Initially, sketch out how you will be making Initially, sketch out how you will be making

your first few contoursyour first few contours Make your lines as smooth as possible.Make your lines as smooth as possible. Ignore outliers, data that doesn’t seem like Ignore outliers, data that doesn’t seem like

it fits with the “big picture.”it fits with the “big picture.” If you need more help, try: tutorial on webIf you need more help, try: tutorial on web

Helpful HintHelpful Hint Think about the contour as a line Think about the contour as a line

separating the observationsseparating the observations with with higher higher valuesvalues on one side of the line, and on one side of the line, and lower lower valuesvalues on the other side: on the other side:

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Draw the25-line:

Helpful HintHelpful Hint Think about the contour as a line Think about the contour as a line

separating the observationsseparating the observations with with higher higher valuesvalues on one side of the line, and on one side of the line, and lower lower valuesvalues on the other side: on the other side:

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Draw the25-line:

Helpful HintHelpful Hint Think about the contour as a line Think about the contour as a line

separating the observationsseparating the observations with with higher higher valuesvalues on one side of the line, and on one side of the line, and lower lower valuesvalues on the other side: on the other side:

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Draw the25-line:

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ExamplesExamples

Say these Say these observations are observations are temperatures. temperatures. Where should Where should we draw the we draw the 1515oo FF isotherm?? isotherm??

ExamplesExamples

Say these Say these observations are observations are temperatures. temperatures. Where should Where should we draw the we draw the 1515oo FF isotherm?? isotherm??

ExamplesExamples

Say these observations are temperatures. Where should we draw the 75oF and 80oF isotherms??

ExamplesExamples

Say these observations are temperatures. Where should we draw the 75oF and 80oF isotherms??

Want extra practice?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 AssignmentIn Class Assignment

To convert from Z time to CST, subtract 6 hours. 05Z = 11 PM CST