How to read barometric pressure on a station model

IL-2: Station Models and Contouring

In this lab we will be learning about reading weather maps. In Part I you will learn about how to read station models, Part II will explore reading weather maps, and in Part III you will apply those skills to an activity.

Part I Understanding Station Models

A station model is a way to depict surface weather station data in a compact way so that it fits on a weather map. This data usually includes, temperature, dewpoint, wind speed and direction, sea level pressure, and cloud cover. They sometimes include some other data as well.

Go through the tutorial below that introduces station models, and how to decode them. Click "Next Page" to access all pages of the tutorial.

http://cimss.ssec.wisc.edu/wxwise/station/index.html (Links to an external site.)Links to an external site.

There are two confusing points I want to go over before we practice our skills.

First, is how to decode pressure readings. The coded pressure on the station model will always be missing the leading 9 or 10. To figure out which, we can use the 500 rule. If the coded pressure is less than 500, then we tack on a 10 to the front. If the coded pressure is greater than 500 we tack on a 9. In both cases, we also move the decimal point over, one position to the left. Here are some examples:

Coded pressure=103; Station pressure=1010.3 mb

Coded pressure=972; Station pressure=997.2 mb

The other tricky point is wind direction. In meteorology, we always discuss the wind as the direction it is coming FROM. So, a wind coming from the southwest and going toward the northeast is considered a southwesterly (SW) wind. On the station model you can consider the wind graphic as the tail to the arrow, and the tail to the arrow is in the direction the wind is coming from, and it is going toward the center of the station model.

To decode the wind we can imagine that the station model is on a map. On the map, north is above, east is to the right, south is below, and west is to the left. So, if the wind graphic is to the bottom left of the center of the station model, then the wind is from the southwest.

To practice what you have learned, go through the Practice Exercises on the tutorial (note, java is needed to see the exercises):

http://cimss.ssec.wisc.edu/wxwise/station/page5.html (Links to an external site.)Links to an external site. OR http://itg1.meteor.wisc.edu/wxwise/AckermanKnox/chap1/decoding_surface.html (Links to an external site.)Links to an external site.

Finally, let's look at some station models on an actual weather map. Navigate to the NCAR Real-time Weather Page:

http://weather.rap.ucar.edu/ (Links to an external site.)Links to an external site.

Click "Surface" to access surface data.

On the map, click on "WMC."

You are now looking at a plot of weather data from surface stations in the western U.S.

Right click (or ctrl-click) and save the image. When submitting the assignment, upload the image along with your other files.

Part II Reading Weather Maps

Now we will learn to read some of the other important parts of weather maps.

The first important component of a weather map are isolines. Isolines are lines of constant value on a weather map. There are different kinds of isolines.

Isobars are lines of constant pressure.

Isotachs are lines of constant wind speed.

Isotherms are lines of constant temperature.

There, are also numerous others. Some of you may be familiar with topographic maps, where the lines indicate lines of constant elevation. Those are another example of isolines.

To see some examples of isolines, navigate to the NCAR Real-time Weather Page:

http://weather.rap.ucar.edu/ (Links to an external site.)Links to an external site.

Click on "Upper-Air." This will bring us to the data that is collected from rawindsondes (also known as weather balloons).

Across from "including contours," click on "500 mb."

You should get a map that includes isolines for the height of the 500 mb pressure surface (black lines) as well as isotherms of temperature at 500 mb (blue dotted lines). Relative humidity above 70% is indicated by green coloring.

Right click (or ctrl-click) and save the image. When submitting the assignment, upload the image along with your other files.

Watch the following video that reviews isolines, introduces fronts (which we will be focusing on later in this course), and discusses how isolines are related to wind.

How to Read Weather Maps (Links to an external site.)Links to an external site. How to Read Weather Maps

Part III Station Models, Weather, and Pressure Maps Activity

Complete the following activity. You can submit your answers in a word file. To add your answers over the graphics inserting a text box will be useful. To add a line to the 500mb map (Q4) you can insert shapes. You will likely need to use your textbook as reference for the activity.

PressureWindLab.doc

Settings

If you have questions about the assignment, please send me a message or start a discussion on Canvas.