Contouring and Map Analysis Lecture 2 February 4, 2010

Today’s Agenda  Attendance  Weather Discussion  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…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 informationBut contouring gives us even more information Contoured maps give easy-to-read, general information about small to large areasContoured maps give easy-to-read, general information about small to large areas Contoured maps help in easily diagnosing and depicting weather features and variablesContoured 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?  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: Draw the 25-line:

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: Draw the 25-line:

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: Draw the 25-line: 25

Examples  Say these observations are temperatures. Where should we draw the 15 o F isotherm??

Examples

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

Examples

Want extra practice? Professor Steve Ackerman has developed a website which allows you to practice contour analysis through a Java-applet:

In Class Assignment

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