NAME DATE PARTNER(S) PREDICTING THE WEATHER How well does your local weatherman do in predicting the weather? Is he or she more accurate for the next day or for a week in the future? Why do you think that it is hard to make very accurate forecasts? List the variables (like temperature) that you think play a part in the weather in a given region for a particular time. Let s Explore! To investigate weather prediction we will be using some activities from the Internet. 1. Locate yourself at a computer with Internet access and launch a browser such as Internet Explorer or Netscape. 2. Go to the following URL: http://academic.pgcc.edu/~bgage/weather.htm 3. After reading through and working on the Predicting the Weather page work through Lessons 1-3. The pages and maps you need as you go along are reproduced with this activity. Use colored pencils as needed. NOTE: The following pages have been reproduced with minor modifications for educational use only from the following site which is no longer available: http://vathena.arc.nasa.gov/curric/weather/hsweathr/index.html Explorations in Earth and Space Science PSC 1210 Prince George s Community College 153
Red sky in morning, sailors give warning. red sky at night, sailors delight. PREDICTING THE WEATHER What does the rhyme mean? It was used by sailors in the United States for many years. Is this old saying true? As a matter of fact, the saying often holds true in the United States. Because the weather patterns in North America generally move from west to east, when clouds arrive overhead at sunrise the sky will appear red, signaling a storm "moving in". When the storm eventually passes, the sky will clear in the western sky. If sunset occurs simultaneously, the light will cast a red glow on the clouds above, now moving towards the east. Sample Four-day forecast View a current four day forecast for your city. This modern, four day weather forecast, obviously relies on more than simply the current observations of the sky. What are the factors that help meteorologists make this forecast? What methods were used to make the predictions? Weather forecasting is not an exact science. It ranges from weather folktale simplicity to elaborate computer simulations that rely on a variety of methods to produce their results. Our focus will be to use common surface level data, as shown on most local TV weather maps, to understand weather patterns. After practice in reading weather maps, you will make maps predicting the weather for the next few days 154 Explorations in Earth and Space Science PSC 1210 Prince George s Community College
across the country. You can then compare your maps with the "experts" and the real weather as it occurs. Activities (Lessons) LESSON 1: ISOBARS LESSON 2: ISOTHERMS LESSON 3: FRONTS Other Information Weather Data Collection Methods Weather Folktales Glossary from The Weather Channel Related Links Teacher Talk Image Credits: Forecast from http://www.intellicast.com/. Maps from The Weather Channel Red sky photo from National Weather Service. An example of NWS services: Interactive Marine Observations Written by: Gene Rempel and Mike Hanson Last Modified September 19, 1998 Explorations in Earth and Space Science PSC 1210 Prince George s Community College 155
LESSON 1: ISOBARS What's the difference between a High and a Low? What kinds of weather are likely to be found in each? Certain weather maps allow us to view High and Low pressure systems that control the weather. An isobar is a line connecting locations of equal barometric pressure. Isobar maps show where pressures are relatively high and low, and show us where pressure changes are gradual or dramatic over a distance. Exercise 1: This activity will assist you in creating and interpreting weather maps with isobars. The image above shows an example of a weather map containing isobars. The thick black lines are called isobars. They are typically placed at intervals of 4 millibars. Select Image 1 and print out the map with pressure readings. 1. Determine which 4 millibar intervals will be necessary to use for this map. (Keep in mind that the isobars are found every 4 millibars such as 996, 1000, 1004, etc.) 2. Draw in the isobars on the map you have printed out. Start with the 1000 mb line, then adding 996 mb, 1004 mb, etc. Label each isobar. Note: isobars form sets of curves that do not cross each other. Isobars can be used to identify "Highs" and "Lows". The pressure in a high is greater than the surrounding air. The pressure in a low is lower than the surrounding air. 156 Explorations in Earth and Space Science PSC 1210 Prince George s Community College
3. Label with an "H" the center of a high pressure area. 4. Label with an "L" the center of a low pressure area. High pressure regions are usually associated with dry weather because as the air sinks it warms and the moisture evaporates. Low pressure regions usually bring precipitation because when the air rises it cools and the water vapor condenses. 5. Over which state would you expect to see rain or snow? 6. Over which state would you expect to see clear skies? In the northern hemisphere the wind blows clockwise around centers of high pressure. The wind blows counterclockwise around lows. It is the opposite in the southern hemisphere. 7. Draw arrows around the "H" on your map to indicate the wind direction. 8. Draw arrows around the "L" on your map to indicate the wind direction. Imagine that you live in El Paso, TX. 9. If a High were approaching you from the west, describe the shift in wind direction as the High approaches you and then passes to the east. 10. How would pressure measurements change as the High approaches and then passes to the east? Imagine that you live in New York City. 11. If a Low were approaching you from the west, describe the shift in wind direction as the Low approaches you and then passes to the east. The strength of the wind is determined by differences in the pressure, the pressure gradient. A large change in pressure over a short distance would indicate strong winds. On a weather map, isobars that are close together indicate a strong pressure gradient. 12. Indicate on your map where you expect the strongest winds (the steepest pressure gradient). Explorations in Earth and Space Science PSC 1210 Prince George s Community College 157
Image Credits: Maps from The Weather Channel Maps from Tiger Census Maps Written by: Gene Rempel and Mike Hanson Last Modified September 19, 1998 LESSON 2: ISOTHERMS Will it be warm outside tomorrow? Certain weather maps allow us to view warm and cold areas in an easy fashion. One helpful weather map contains isotherms. An isotherm is a line connecting locations with equal temperature. Isotherm maps show where temperatures are relatively high and low, and also where temperature changes are gradual or dramatic over a distance. This image shows an example of a weather map containing 60 and 70 isotherms. The large black lines are called isotherms. They are typically placed at intervals of 10 degrees Fahrenheit. Exercise 2: This activity will assist you in creating and interpreting weather maps with isotherms. Select Image 2 and print out the map with temperature readings. 1. Determine which 10 degree intervals will be necessary to use for this map. 2. Draw in the isotherms on the map you have printed out. Label each isotherm. 158 Explorations in Earth and Space Science PSC 1210 Prince George s Community College
Isotherms can be used to identify air masses (large areas of the lower atmosphere with similar weather). Air masses are generally referred to as cold or warm. Cold air masses are colder in the center, and warm air masses are warmer in the center. 3. Name a state over which a cold air mass is located. 4. Name a state over which a warm air mass is located. Air masses are also categorized as dry or humid. Humid air masses develop over ocean waters. Dry air masses come from large land areas. An air mass found over the Gulf of Mexico would be humid and warm. An air mass located in central Canada in winter would be dry and cold. 5. How would you describe the air mass moving into the United States from Canada? Activities (Lessons) LESSON 1: ISOBARS LESSON 2: ISOTHERMS LESSON 3: FRONTS LESSON 4: WEATHER PREDICTION LESSON 5: WEATHER PATTERNS LESSON 6: WEATHER PROVERBS Part A and Part B Other Information Weather Data Collection Methods Weather Folktales Glossary from The Weather Channel Weather Links Teacher Talk Image Credits: Maps from The Weather Channel Maps from Tiger Census Maps Written by: Gene Rempel and Mike Hanson Tell us what you think about this page. Last Modified September 19, 1998 Explorations in Earth and Space Science PSC 1210 Prince George s Community College 159
LESSON 3: FRONTS What happens along cold fronts and warm fronts? The boundary between two air masses is called a front. As a result, moving fronts indicate a change in the weather. On a weather map fronts are drawn where there is large change in temperature and a shift in wind direction. A front can also be described as the boundary between adjacent Highs with different conditions. On a weather map, fair weather is generally associated with Highs while stormy weather is associated with Lows and with the portions of fronts that extend from them. Highs and Lows are usually hundreds or thousands of miles across. Both Highs and Lows tend to travel from west to east across the United States, bringing changing weather as they move. The image above shows an example of a weather map containing a warm and cold front. A cold front means a cold air mass is pushing into a warmer air mass, and is shown with blue sharp "teeth" pointing the direction of the moving cold air. A warm front means a warm air mass is pushing into a colder air mass, and is shown with red rounded "teeth" pointing the direction of the moving warm air. Exercise 3: This activity will assist you in interpreting weather maps on which fronts are already identified. Use the map above to complete the following activity. 160 Explorations in Earth and Space Science PSC 1210 Prince George s Community College
Imagine that you are located at El Paso, Texas on the map. 1. As the cold front approaches, what changes in the sky condition do you expect? 2. What changes in wind direction will occur as the front passes? 3. At the time the front passes what change in temperature will occur? Imagine that you are located at New York City, New York on the map. 4. What changes will occur in the sky condition prior to the arrival of the warm front? 5. As the warm front passes, what changes do you expect in wind direction? 6. After the front passes, what changes in weather do you predict? The rainfall is usually different along cold fronts and warm fronts. Along cold fronts, the air is pushed up rapidly and the front quickly passes. The rain is often more stormy and relatively brief. Along warm fronts, the air is pushed more slowly over the cold air mass. The rainfall is usually more gentle and extended in duration. 7. Over which city, New York or El Paso, are thundershowers more likely to occur? Why? 8. Fill in the characteristics of High pressure and Low pressure systems in the table below. Characteristic HIGH LOW Pressure Surface Winds Sky Conditions Explorations in Earth and Space Science PSC 1210 Prince George s Community College 161
Other Information Weather Data Collection Methods Weather Folktales Glossary from The Weather Channel Weather Links Teacher Talk Image Credits: Maps from The Weather Channel Maps from Tiger Census Maps Written by: Gene Rempel and Mike Hanson Last Modified September 19, 1998 Activity: Weather Prediction Now it s time to see if you can use the information you learned to make weather predictions. 1. Your group will be given two sets of weather maps for three days. A specific location will be identified with each set. From these complete the chart at the end of this activity for the first three days. Then predict the weather for the next two days for the specified locations. 2. The weather maps for the next two days are available. When you have made the predictions compare your predictions to the maps. How well did you do? Explain. 162 Explorations in Earth and Space Science PSC 1210 Prince George s Community College
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City Dates Date Actual weather Predicted Weather Explanation for Weather Explorations in Earth and Space Science PSC 1210 Prince George s Community College 165
City Dates Date Actual weather Predicted Weather Explanation for Weather 166 Explorations in Earth and Space Science PSC 1210 Prince George s Community College