A STUDY OF WEATHER MAPS 257 



States. Figure 179 is the morning weather map of December 

 4, 1906, and shows the LOW centered over Colorado and 

 HIGHS over western Pennsylvania and the Canadian plains. 

 The inflowing winds about the LOW and the outflowing winds 

 of the HIGHS are well illustrated. Note also the sheet of 

 clouds surrounding the LOW, and the smaller area of rain. 

 The isotherms show low temperature in the eastern HIGH and 

 a warm area about the LOW. Figure 180, the morning map of 

 December 5, gives a fine example of the circling winds about a 

 LOW and of the warm wave extending from the south and 

 southeast up to the center of the LOW. The cloud area is 

 broader and the rain area much larger than the day before. 

 Figure 181, the map for December 6, shows the warm wave 

 shifted eastward with the LOW. The rain area is still broader. 

 A HIGH is coming from western Canada toward the Mississ- 

 ippi valley. Another center of high pressure is seen in the 

 southwest. 



281. Changes Caused by the Passing of the Storm ; How 

 the Barometer Changed. Notice that on the morning of 

 the 5th, the isobars show that the pressure at Omaha was 

 29.60 in. and at Detroit 30.16 in., while on the 6th, the 

 pressure at Omaha was 30.20 in. and at Detroit, 29.30 in. 

 What change in the barometer occurred at Detroit as the 

 storm approached? What change at Omaha as the storm 

 departed? Describe the change that must have occurred at 

 Chicago during the same 24 hours. What change in barom- 

 eter at Pittsburg? At St. Louis? If you had a barometer, 

 could you, by watching its changes, learn anything about the 

 movements of LOWS that cross your portion of the continent? 

 If your barometer fell steadily for several hours, what would 

 that indicate? After falling quite low, if it began a steady rise, 

 what would that indicate? 



If the pressure at the storm center on December 5 had been 

 half an inch lower, with the storm moving at the same speed, 

 would that have made any difference in the rate of rise or fall 

 of the barometer at those cities near its path? Suppose the 



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