III: WEATHER MAP WATCH I N T H I S S E C T I O N O F ‘ W E A T H E R W I S E ’ Y O U W I L L L E A R N A B O U T W E A T H E R M A P S A N D F O R E C A S T I N G . z z 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 half- circles. What does all that mean? And how do we know where to draw all those lines? I’m here to explain A solar-powered Surface all these puzzles to Automated Measurement you. We will also take a trip back in time to year 1922. Do you think (SAM) site. Photo from NOAA photo weather maps were different back then? Remember, we didn’t have library. computers! In order to make accurate weather forecasts, we also need observations of Observations 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 map is having observations. There are let’s discuss these first. All surface thousands of weather stations all over observations are coordinated and taken the world that collect measurements of at the same time. Observations are also atmospheric pressure, temperature, collected and recorded in the same precipitation, wind, and cloudiness. manner for consistency. Surface data are Most surface observations are taken in recorded using a ‘station model’. areas that are densely populated. III.1 Station Model Have you ever wondered how weather 4. To show the wind direction, we draw a line information is recorded? And how was it away from the circle in the direction in which the recorded 100 years ago? wind is coming from: It turns out that surface weather measurements North are being recorded in the same way as 100 years ago, using a station model. A station model is a West East diagram which uses a combination of numbers 55 012 and drawings to describe the weather. Today you will learn about a simplified station model that In the above case, the wind is coming from the North-East. shows only cloud cover, temperature, pressure, wind direction, and wind speed. 5. Finally we show the wind speed by adding 1. To draw a station model, we start with a circle: ‘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 2. We leave the circle empty if the sky is clear and than 1 mile per hour of wind.) For example, the color it in in proportion to the cloudiness. For picture below depicts wind strength of 25 knots: example: if we can’t see the sky anymore because clouds are everywhere, we fill in the circle 10 knots entirely: +10 knots + 5 knots 55 012 = 25 knots 3. We then write down the temperature to the left of the circle (above the center line) and the If the winds are strong we use a flag to mark 50- pressure to the right of the circle: knot winds. So the wind in the following picture is 55 012 60 knots: 50 knots temperature pressure +10 knots 55 1012 On the map you will see on the next page, = 60 knots pressure is reported in inches of mercury, and the DEN first digit is skipped. So ... 012 means 30.12 and if the number starts with a 9 the pressure is 29.XX. Finally, we note the name of the station with a So, 987 means pressure of 29.87 inches of three letter symbol. The Denver airport station mercury. It’s a little confusing, I know! has a symbol DEN. III.2 Decipher the Weather Code ! In this fun game you will practice decoding the NOW, let’s play another game: station model observations. Work in groups of 3! 1. Pick one girl scout in your three-person group DIAGRAM 1 to write down the weather (it can be from Decode the following station model: anywhere or you can make it up): Cloudiness:! _______________________ Temperature:! _______ Pressure:! _______ 50 015 Wind Speed:! _______ Wind dir. from ________ Write down the following: 2. Have the other two group members draw a station model of the weather in the space below. Cloudiness:! _______________________ Temperature:! _______ Pressure:! _______ Wind Speed:! _______ Wind Direction: from __________ DIAGRAM 2 Decode the following station model: 3.Repeat the above 2 steps: Cloudiness:! _______________________ 88 995 Temperature:! _______ Pressure:! _______ Wind Speed:! _______ Wind dir. from ________ Station model: Cloudiness:! _______________________ Temperature:! _______ Pressure:! _______ Wind Speed:! _______ Wind Direction: from __________ III.3 The following picture shows a fewRead selected surface the observations Map collected 1 over the United States at one time on Feb 1, 2006. y r s e w alue v it is v e r the e he high or lo r he d). is w gions w gions of e e e r ssur cle e totally fille e , cir r s ar ke y mostly in r cle , high pr r cir mbe the e me r e he ? R e y (w ith a GREEN mar stion: Is it cloud ssur e 2. W cloud Que pr start with a ‘0’. _______________________________________________ ______________________________________________ UE ss than s of z he s le alue v e ssur e r than 30 inc ead station models. On te pr a e r the s g cle alue , cir r v e y (starting with a 9) and BL ke ssur cur r e pr Read the Map me cle z s of y (starting with a 0) r cir he ith a RED mar ke cur e is an opportunity for you to r r Her the above map: 1. W 30 inc mar me III.4 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. z z 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 L regions of higher atmospheric 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 Historical Perspective Weather maps today are made with the help of EATHER TATION computers. Computers today can draw contours W ‘S ’ and generate colorful weather maps. But do you In Norway back in the early 1900’s, weather know how this was done in the 1920’s? 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 Jacob Bjerknes, year 1920 Bergen, Norway Photo courtesy of Mel Shapiro assistants. Meteorologists would draw the maps, and based on that map and previous maps they PORTRAIT OF A WEATHERMAN would make a forecast for the next days. 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 Tor Bergeron (l) Jacob Bjerknes (r) and assistant at work 1919. in his career he discovered El Nino. Bergen, Norway Photo courtesy of Mel Shapiro MileHi Girl Scout Council, you Does it look different in will find in it a copy of a comparison to the modern HAND-DRAWN map from weather maps? If you Bonus:picked up the 1958. Can you believe how WeatherWise Kit from the smoothly this map is drawn? III.6 Temperature Map: Although meteorologists are very concerned with air pressure, most people typically want to know the air temperature.