WEATHER OBSERVATIONS (IV-1)

The problem. Observations of the weather began early in the development of intelligence in the human race, and the importance of weather predictions was early recognized. The later invention of the telegraph made it possible to distribute weather observations and forecasts, so that weather bureaus have been organized in almost every civilized country. Each of the United States Weather Bureau stations is in charge of one or more trained observers and is equipped with mercurial barometers, thermometers, wind vane, rain and snow gauge, wind velocity instruments (anemometers), sunshine recorders, barographs, thermographs, and other devices for making a continuous record of weather changes. A close study of the weather forecasts with the actual weather for the time covered shows that the forecasts are correct in about 90 of each 100 cases. How are weather observations recorded and used?

What to use. Barometer, thermometer, daily weather report from the newspaper or weather map, and large sheets of crosssection paper.

What to do. 1. Previous to this experiment the daily weather map should have been secured from the Weather Bureau office of your forecast district. In figure 11 is given a map by means of which you may locate your own chief station, which is at the city. named in your own weather-bureau district.

2. Consult the table on page 12 of the text. What should be the approximate barometer reading for the elevation of your locality? Assume that the variation of the barometer height in different types of weather will be two inches. Mark off a vertical scale on the first sheet of cross-section paper provided in connection with this problem to represent this variation on the barometer chart.

3. Keep a record of the atmospheric pressure from day to day for one month. If no barometer is available the readings can be obtained from the weather map.

4. Use the other cross-section sheet in this problem to make a record of the temperature changes. The general condition of winds, clouds, etc. should be placed at the bottom of the chart.

5. It will be interesting to make a graph for the relative humidity of the station issuing the map. The relative humidity values can be obtained from the weather map.

Questions. What is the average height of the barometer in your locality? the highest reading? the lowest? What relation exists between a low pressure on the one hand, and the temperature, relative humidity, clouds, and wind? What kind of weather accompanies a high pressure?

Suggestions for report. Compare your readings with those placed on a large chart (9 inches wide and 36 inches long) which has been made in your laboratory based upon the plan of the chart on page 36 of the manual. This large chart can be

made by teacher, or teacher and pupils working together, and should be based upon daily records. It is designed to serve as a check upon the work of individual pupils.

Reference work. Read sections 38 to 43. Can you predict the weather that will accompany a low pressure? a high pressure?

Optional problems. Prepare a diagram to explain how a barograph makes a continuous record of the changing air pressure. In a similar way show how the thermograph keeps a record of the changing temperature.

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THE DAILY WEATHER MAP (IV-2)

The problem. The Weather Bureau is best known to the public through the daily report and weather map. The procedure is indicated in the Weather Bureau Report for 1916, which says: "Within two hours after the morning observations have been taken the forecasts are telegraphed from the forecast centers to about 1600 principal distributing points, whence they are further disseminated by telegraph, telephone, wireless telegraphy, and mail. The forecasts reach nearly 90,000 addresses daily by mail, the greater part being delivered early in the day and none later, as a rule, than 6 P.M. of the day of issue, and are available to more than 5,500,000 telephone subscribers within an hour of the time of issue." What information can be obtained from a weather map?

What to use. Supply of daily weather maps. Special bulletins entitled "Explanation of the Weather Map," and "The Weather Bureau," which may be secured from the Weather Bureau, Washington, D. C.

What to do. 1. The teacher and students should study together a daily weather map, as follows: Under "Explanatory Notes " find answers to the following questions:

a. At what time of day are the observations taken?

b. Why is the air pressure for different cities reduced to sea level?

c. What is an isobar?

d. What is the pressure on the isobar nearest your location? e. What is an isotherm?

f. What is the temperature on the isotherm nearest your location?

g. How are the different conditions of weather indicated ? h. Describe the weather in New York, Chicago, Seattle.