Investigation 11.3 Weather Maps

Transcription

1 Name: Date: Investigation 11.3 Weather Maps What can you identify weather patterns based on information read on a weather map? There have been some amazing technological advancements in the gathering and analyzing of atmospheric data over the last century. Despite the use of satellites, computers, and complex programs used to search out patterns, predicting the weather in any given location can only be done reliably for no more than five to seven days in the most ideal of conditions. Many times the best predictions come down to looking at basic atmospheric conditions. In this investigation you will analyze the national weather forecast and make inferences as to what causes differences in weather across the nation. Important symbols on a weather map Cold fronts and warm fronts On a weather map, a cold front is shown using a line marked with blue triangles. The triangles point in the direction the front is moving. A warm front is shown using a line marked with red semicircles, which point in the direction the front is moving. A cold front occurs when cold air moves in and replaces warm air. The warm air is forced sharply upward by the cold, denser air. The rising warm air cools. This causes condensation. Often, rain or snow showers that can be shorter in duration but intense, accompany a cold front. As a cold front moves through an area, the temperature and water content of the air decrease rapidly. A warm front occurs when warm air moves in and replaces cold air. The warm air slides up over the colder air. The warm air rises and cools, but in this case the lifting is very gradual and steady. As a result, long bands of light precipitation often move ahead of a warm front. As a warm front moves through an area, there will be a noticeable increase in temperature and moisture in the air. High-pressure and low-pressure centers A high-pressure center tends to be found where a stable, colder air mass has settled in a region. Colder air is denser than warm air, and therefore creates higher atmospheric pressure. Sinking air in a high-pressure center inhibits the development of the upward air movement needed to create clouds and precipitation. High-pressure centers, therefore, are associated with fair weather and blue skies. Winds rotate clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. This is the opposite of what happens in a low-pressure center. When a cold front moves into a region and warm air is forced upward, a low-pressure center is created near Earth s surface at the boundary of two air masses. Cold air rushes in to fill that low-pressure region. This cold air forces more warm air to be pushed upward. A cycle begins to develop. Due to the Coriolis effect, the air masses move in curved paths. As a result, the moving air begins to rotate around the low-pressure center. In the northern hemisphere, the moving air rotates counterclockwise, while in the southern hemisphere, the air rotates clockwise. Strong winds and precipitation often accompany these rotating systems. Analyzing temperature Analyzing temperature Study the national weather forecast from a daily newspaper or a reputable internet weather reporting website. Locate the list of the temperature and sky cover in cities around the country. Also, locate the weather map showing Investigation Answer Sheet: Weather Maps p.1

2 sunny regions, the temperature, high- and low-pressure regions, and fronts. Record the high and low temperatures for cities in the table below. Then find the difference between the two temperature readings. Sky cover and pressure will be filled in later. Table 1: Weather data City High Low Temp difference Sky cover Pressure Seattle, Washington Los Angeles, California Las Vegas, Nevada Phoenix, Arizona Atlanta, Georgia Tampa, Florida San Francisco, California Oklahoma City, Oklahoma New Orleans, Louisiana Kansas City, Kansas Tucson, Arizona Denver, Colorado Dallas, Texas Houston, Texas Minneapolis, Minnesota Memphis, Tennessee Chicago, Illinois Miami, Florida New York, New York Baltimore, Maryland Investigation Answer Sheet: Weather Maps p.2

3 What causes the wide variety of temperature conditions across the map? Use Table 1 to respond to the following questions. It will also be helpful for you to study a map of the United States that includes the Pacific and Atlantic Oceans and details about major topographical features. a. Give examples of differences in the cities high temperatures due to latitude. For example, Dallas, Texas, is in a lower latitude than Seattle, Washington. Explain why these differences exist. b. Give examples of differences in the cities high temperatures due to geographical features such as the Pacific Ocean, the Rocky Mountains, the Great Lakes, or the Atlantic Ocean. Explain why geography influences temperatures. c. Fill in the table for the sky cover for each city. How does the sky cover affect the temperatures of cities near the same latitude? Why do you think this is? What does atmospheric pressure tell us about the weather? a. On your weather map, over which states are areas of high pressure centered? Over which states are low pressure areas centered? b. In the sixth column of the table (the heading is Pressure), record whether you think each city is in a region of high pressure, low pressure, or in-between. c. What kind of cloud cover or weather is associated with high-pressure regions? Look at the sky cover for the cities in the high-pressure regions. What do you think the humidity is like in these regions? Investigation Answer Sheet: Weather Maps p.3

4 d. What kind of cloud cover or weather is associated with low-pressure regions? Look at the sky cover for the cities in the low-pressure regions. What do you think the humidity is like in these regions? e. Locate the fronts shown on the weather map. The flags on the fronts tell us the direction of the wind. The cold fronts are symbolized by triangular flags, the warm fronts by semicircular flags. Are fronts associated with high- or low-pressure regions? f. What type of weather is associated with a warm front? What type of weather is associated with a cold front? g. Based on what you have learned so far about low- and high-pressure regions, let s investigate the effect they have on the wind. High-pressure regions tend to push air toward low-pressure regions. Do you think the air in a low-pressure region tends to sink or rise? Does the air in a high-pressure region sink or rise? h. Based on those conclusions, how do you think low-pressure regions contribute to the formation of rainstorms? i. Precipitation occurs when warm, moist air is cooled to a certain temperature called the dew point. At the dew point temperature, water in the air condenses into droplets of water called dew and soon these droplets fall out of the sky as precipitation. Why would a low-pressure region be a good place for a volume of air to reach the dew point temperature? Investigation Answer Sheet: Weather Maps p.4

5 j. Pick five cities from Table 1 in different areas around the country and predict what you think the weather will be in those cities for the next five days based on what you have learned today. Write your predictions down and check back with a newspaper or Internet weather reporting service each day to check up on your predictions. Be sure to include the reasons you are predicting the weather you forecast for each area. Write up a summary of how well your predictions went and present them to your class after the five days have passed. Investigation Answer Sheet: Weather Maps p.5