Contouring and Map Analysis AOS 101 September 22, 2009

Today’s Agenda Attendance / Turn in homework Quiz 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… 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 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: 19 17 19 22 Draw the 25-line: 24 20 30 21 21 27 25 23 24 29 29 30 30 24

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 17 19 22 Draw the 25-line: 24 20 30 21 21 27 25 23 24 29 29 30 30 24

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 17 19 22 Draw the 25-line: 24 20 30 21 21 27 25 23 24 29 29 30 30 24 25

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