78 STORMS AND WEATHER FORECASTS 



ture can occur until the high pressure of the northwest is rei)laced 

 by a low pressure, and convectional currents are drawn toward 

 the northwest instead of being forced southward from that region. 



To summarize in regard to cold waves, it may be said that 

 when the charts indicate tiie formation of a body of dense, cold 

 air in the northwest, as shown by the barometer readings, the 

 skilled forecaster is on the alert. He calls for special observa- 

 tions every four hours from the stations within and directly in 

 advance of the cold area, and as soon as he becomes convinced 

 that the cold wave will sweep across the country with its attend- 

 ant damage to property, destruction to animal life, and discom- 

 fort to humanity, the well-arranged system of disseminating 

 warnings is brought into action, and by telegraph, telephone, 

 flags, bulletins, maps, and other agencies the people in every 

 city, town, and hamlet, and even in ftirming settlements, are 

 usually notified of the advancing cold twelve, twenty-four, or 

 perhaps even thirty -six hours before it reaches them. 



Charts XIV and XV show the cyclonic systems prevailing at 

 8 p. m. on the days of the Louisville and St Louis tornadoes. 

 Several tornadoes occurred on each day; their tracks are shown 

 by rows of crosses in the southeast quadrants of each cyclone. 



Especially do I wish to emphasize the distinction between the 

 cyclonic storm and the tornado. The press and nine out of ten 

 people who should know better use these terms as sjmon^nnous. 

 The cyclone shown on Chart XIV, which is fairly typical of all 

 cyclones, is a horizontally revolving disk of air, covering the 

 whole United States from the Atlantic ocean westward to and 

 including the Mississippi valley, with the air currents from all 

 points flowing spirally inward toward the center, while the tor- 

 nado is a revolving mass of air of only 500 to 1,000 yards in 

 diameter, and is simply an incident of the cyclone, nearly always 

 occurring in its southeast quadrant. The cyclone may cause 

 moderate or high winds through a vast expanse of territory, 

 while the tornado, with a rotary motion almost unmeasurable, 

 always leaves a trail of death and destruction in an area infini- 

 tesimal in comparison to the area covered by the cyclone. 



The tornado is the most violent of all storms, and is more fre- 

 quent in the central valleys of the United States than elsewhere. 

 It has characteristics which distinguish it from the thunder- 

 storm, viz., a pendent, funnel-shaped cloud and a violent, rotary 

 motion in a direction contrary'- to the movements of the hands 

 of a watch, together with a violent updraught in the center. 



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