I N T H I S S E C T I O N O F W E AT H E RW I S E YO U W I L L L E A R N A B O U T W E AT H E R

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1 III: WEATHER MAP WATCH I N T H I S S E C T I O N O F W E AT H E RW I S E YO U W I L L L E A R N A B O U T W E AT H E R MAPS AND FORECASTING. What is a Weather Map? Well, that s a simple question. It s a map that shows us weather! But how? What are all those lines on a weather map? And what about the symbols? Often on maps we see large H s and L s, blue and red lines with triangles and halfcircles. What does all that mean? And how do we know where to draw all those lines? A solar-powered Surface Automated Measurement (SAM) site. Photo from NOAA photo library. I m here to explain all these pules to you. We will also take a trip back in time to year Do you think weather maps were different back then? Remember, we didn t have computers! In order to make accurate weather forecasts, we also need observations of weather over the oceans. These come from buoys and ships. The surface The first step towards making a weather observations are most relevant to us, so let s discuss these first. All surface map is having observations. There are thousands of weather stations all over observations are coordinated and taken the world that collect measurements of at the same time. Observations are also collected and recorded in the same atmospheric pressure, temperature, manner for consistency. Surface data are precipitation, wind, and cloudiness. recorded using a station model. Most surface observations are taken in areas that are densely populated. Observations III.1

2 Station Model Have you ever wondered how weather information is recorded? And how was it recorded 100 years ago? It turns out that surface weather measurements are being recorded in the same way as 100 years ago, using a station model. A station model is a diagram which uses a combination of numbers and drawings to describe the weather. Today you will learn about a simplified station model that shows only cloud cover, temperature, pressure, wind direction, and wind speed. 1. To draw a station model, we start with a circle: 2. We leave the circle empty if the sky is clear and color it in in proportion to the cloudiness. For example: if we can t see the sky anymore because clouds are everywhere, we fill in the circle entirely: 3. We then write down the temperature to the left of the circle (above the center line) and the pressure to the right of the circle: temperature pressure On the map you will see on the next page, pressure is reported in inches of mercury, and the first digit is skipped. So means and if the number starts with a 9 the pressure is 29.XX. So, 987 means pressure of inches of mercury. It s a little confusing, I know! 4. To show the wind direction, we draw a line away from the circle in the direction in which the wind is coming from: North West In the above case, the wind is coming from the North-East. 5. Finally we show the wind speed by adding barbs and flags to the wind direction line: Each full barb represents winds of 10 knots, each half barb is 5 knots, etc. (1 knot of wind is a little less than 1 mile per hour of wind.) For example, the picture below depicts wind strength of 25 knots: East If the winds are strong we use a flag to mark 50- knot winds. So the wind in the following picture is 60 knots: DEN 10 knots +10 knots + 5 knots = 25 knots 50 knots +10 knots = 60 knots Finally, we note the name of the station with a three letter symbol. The Denver airport station has a symbol DEN. III.2

3 Decipher the Weather Code! In this fun game you will practice decoding the station model observations. Work in groups of 3! DIAGRAM 1 Decode the following station model: Write down the following: Cloudiness:! NOW, let s play another game: 1. Pick one girl scout in your three-person group to write down the weather (it can be from anywhere or you can make it up): Cloudiness:! Temperature:! Pressure:! Wind Speed:! Wind dir. from 2. Have the other two group members draw a station model of the weather in the space below. Temperature:! Pressure:! Wind Speed:! Wind Direction: from DIAGRAM 2 Decode the following station model: Repeat the above 2 steps: Cloudiness:! Temperature:! Pressure:! Wind Speed:! Wind dir. from Station model: Cloudiness:! Temperature:! Pressure:! Wind Speed:! Wind Direction: from III.3

4 Read the Map 1 The following picture shows a few selected surface observations collected over the United States at one time on Feb 1, Read the Map Here is an opportunity for you to read station models. On the above map: 1. With a RED marker, circle the pressure values less than 30 inches of mercury (starting with a 9) and with a BLUE marker circle pressure values greater than 30 inches of mercury (starting with a 0) 2. With a GREEN marker, circle regions where it is very cloudy (where the circles are totally filled). Question: Is it cloudy mostly in regions of high or low pressure? Remember, high pressure is where the values start with a 0. III.4

5 Drawing a Weather Map You have learned now how to record surface weather observations. It s time now to learn how they are transformed into a weather map! LOOK AT ALL THOSE SYMBOLS! On page 3 you looked at a weather map with only selected surface observations collected over the United States. Now, let s take a look at ALL of the observations taken at that time. Look at all those symbols! You can hardly see anything! There must be a better way to look at observations! You re absolutely right! There is a better way and it involves contouring. Contouring! Contouring is a process similar to playing connect-the-dots : each contour connects places where a given quantity is the same. On a weather map we typically contour pressure or temperature. The map below is a contour map of pressure created from the observations shown on the previous page. Do you understand now what the blue H s and red L s represent? Compare this to your map! The H s on a weather map mark regions of higher atmospheric L pressure, and the L s mark regions of lower atmospheric pressure. Where do you see stormy (rainy/snowy) weather? Is it near regions of low or high pressure? That s right! Bad weather is usually associated with regions of LOW atmospheric pressure. That s why meteorologists are very concerned with accurately measuring pressure. III.5

6 Historical Perspective Weather maps today are made with the help of computers. Computers today can draw contours and generate colorful weather maps. But do you know how this was done in the 1920 s? Jacob Bjerknes, year 1920 Bergen, Norway Photo courtesy of Mel Shapiro PORTRAIT OF A WEATHERMAN IN 1920 The above photo depicts Jacob Bjerknes - a pioneer of modern weather forecasting. He was the first to introduce the concept of fronts into the model of winter storms. He also explained the association of clouds and rain to fronts. Jacob lived in Norway, and came to America in the 1940 s to become a meteorology professor at the University of California at Los Angeles. Later on in his career he discovered El Nino. WEATHER STATION In Norway back in the early 1900 s, weather offices were quite different to what they are today. Instead of a fancy office building, meteorologists sometimes used the upstairs of their home as a place to work. The crucial working equipment consisted of large tables on which weather maps were drawn by hand. Information from various weather stations was transmitted via telegraphs throughout the world. It took meteorologists about two hours to prepare a hand-drawn weather map and issue a forecast. The meteorologists were not drawing the station models on the maps - that was the job of the assistants. Meteorologists would draw the maps, and based on that map and previous maps they would make a forecast for the next days. Tor Bergeron (l) Jacob Bjerknes (r) and assistant at work Bergen, Norway Photo courtesy of Mel Shapiro Bonus: If you picked up the WeatherWise Kit from the MileHi Girl Scout Council, you will find in it a copy of a HAND-DRAWN map from Can you believe how smoothly this map is drawn? Does it look different in comparison to the modern weather maps? III.6

7 Temperature Map: Although meteorologists are very concerned with air pressure, most people typically want to know the air temperature. After all, this in large part determines what clothes we are going to wear! The map on the right shows contours of the surface air temperature corresponding to the maps shown on the previous pages. Not surprisingly, warmer temperatures are found in the southern portion of the United States and coldest temperatures are in the north. Note that temperature contours are drawn in 5F intervals. Hence, on a map we see the following contours:... 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, Try Contouring! Let s have some fun and let s draw a pretty weather map! Hope you have lots of colorful markers! On the next page you will find another copy of a map with selected surface observations. This time we re going to look at the temperature which is noted to the left of the circles on the station models. To make things easy we will draw contours every 10F, so the contours will be: 70, 60, 50, 40, 30, 20. To get you started the 70F contour has already been drawn for you. WHAT TO DO? 1. Pick a marker color! Look above the 70F contour and circle all the temperatures between 60F and 69F. 2. Pick another marker color! Now, with it circle temperatures that are between 50F and 59F. 3. Using a PENCIL, draw a contour, separating the circles of different color. Note that temperatures higher than 60F are on one side of the contour, and temperatures lower than 60F are on the other side! 4. Pick another marker color! Now, with it circle temperatures between 40F and 49F. 5. Using a pencil or a marker, draw a contour, separating the circles of different color. 6. Pick another marker color! Now, with it circle temperatures between 30F and 39F. 7. Using a pencil or a marker draw a contour, separating the circles of different color. 8. Pick another marker color! Now, with it circle temperatures between 20F and 29F. 9. You re almost done - now shade the areas between the pencil contours with markers of the same color as your circles! III.7

8 Read the Map 2 The following picture shows a few selected surface observations collected over the United States at one time on Feb 1, F Contour the Map Using instructions on the previous page, contour temperature on the above map. HINT: To the right are the temperature ranges that you will mark with different colors. Circle each temperature range with your marker of choice so you don t forget which color represents which temperatures. 70F 70F - 80F!! 60F - 70F!! 50F - 60F 40F - 50F!! 30F - 40F!! 20F - 30F III.8

9 More Symbols? By now you understand most of the features of a typical weather map. Are there more symbols on it that pule you? What about the red lines with half-circles and blue lines with triangles? Those mark fronts. Fronts A FRONT IS A BOUNDARY BETWEEN TWO AIR MASSES OF DIFFERENT TEMPERATURES When a cold air mass (e.g., air from Alaska) is approaching a region of warm air (for example from the Gulf of Mexico), we see a region of transition on the boundary between the two air masses. We call that region a cold front. Cold fronts typically move from the northwest towards the southeast, as that s where the cold air comes from. Cold Front Cold Warm Cold fronts are marked with a blue line with blue triangles. The pointy side of the triangles shows the direction in which the front is moving. On the other hand, if a warm air mass is approaching a cold air mass, the transition region is called a warm front. Warm air masses, and hence warm fronts, come from the southwest and move towards the northeast. Warm Cold Warm Front Warm fronts are marked with a red line with red half-circles. The round side of the halfcircles shows the direction in which the front is moving. Sometimes air masses don t move very fast. When an cold air mass meets a warm air mass and they are just sitting next to one another, we call the transition region between them a stationary front. Stationary Front Cold Warm A stationary front is marked with blue triangles and red half-circles. The triangles point in the direction in which the cold air wants to move and the circles point in the direction in which the warm air wants to move. III.9

10 One more front... There is one more type of front that we need to discuss: the occluded front. This type of front is often associated with big storms crossing the United States. An occluded front occurs when a cold front catches up to a warm front. How does that happen? Warm and cold fronts usually occur near one another when there is a low pressure system, or an area of low pressure: Cool Eventually, the cold front catches up to the warm front, and an occluded front forms where the warm and cold front met: Very Cold Warm Occluded Front Cool Very Cold Warm An occluded front is marked with a purple line with triangles and half-circles. In this case we have then really cold air behind the cold front, we have very warm air in front of the cold front and behind the warm front, and we have cool air in front of the warm front. Cold fronts tend to move a lot faster than warm fronts, so after some time, the cold front is closer to the warm front: Very Cold Warm Cool Front Skills Here is your chance to practice what you have learned about fronts! Look at a weather map and see if you can identify the different types of fronts that you learned about. What is the most common type of front? Look for areas of low and high pressure. Are they typically near fronts? Describe. III.10

11 Forecasting Weather forecasting is quite a difficult skill. It takes a lot of practice to master it! Do you want to try? Remember, even the professional meteorologist don t get the forecast right all the time! The first step towards forecasting the weather is understanding why we have the current weather. Go back to the weather map on page 4 - can you explain why it is rainy and stormy in some areas, and nice in others? Let me give you one additional hint: Clouds and rain come from water in the atmosphere. has the greatest amount of moisture where there is a lot of surface water: for example, over the oceans and over large lakes. Therefore, a cold front coming from the Pacific Ocean towards Seattle is likely to cause a lot of rain there. A cold front, passing through Colorado usually will bring cold temperatures and strong winds, but not so much rain. Weather Map Watch is a part of WeatherWise - a learning kit designed to teach basics of weather, weather instrumentation, and atmospheric science related careers to Girl Scouts. For more information visit: or contact Jadwiga (Yaga) Richter at beres@ucar.edu WeatherWise was created as part of the Education and Research Visiting Fellowship at the Cooperative Institute for Research in Environmental Sciences at the University of Colorado at Boulder by Jadwiga (Yaga) Richter. Predict the Weather Now it s time for you to become a meteorologist! 1. Pick a place for which you would like to make a forecast: 2. Write down the weather today: 3. Write down why do you think we re having that weather: 4. On a newspaper or TV weather map, look to the northwest and southwest of your location. Are there any cold or warm fronts approaching? 5. Make a forecast for the next day: 6. Next day: Check if your forecast was correct. If you weren t exactly right, listen to a meteorologist on TV explaining the forecast and try to figure out what you missed. Repeat steps 4 through 6 and don t forget to have fun! III.11