WEATHER FORECASTS. 



311 



bars." The heavy, arrow-tipped lines show the actual direction of 

 the wind as it was observed on this occasion. It will be seen that 

 the winds flow spirally outward from the highs in the direction of 

 motion of the hands of a watch, while they blow from the high 

 spirally inward toward the center of the low in the opposite direction 

 to that of the watch's hands. These same directions will always be 

 found about a well-defined high or a low. A severe storm and a 

 low will always be found together, and the law of the winds about a 

 low enables navigators to judge of the direction of the center of the 

 storm and to steer away from it in time to avoid disaster. The lows 

 are called cyclones, because of the inward direction of their winds; 

 and the highs are known as anticyclones, because the winds result- 

 ing from them flow outward. 



The highs are caused by descending currents from the upper 

 air due to increased density which results from cooling by radiation 

 of heat from the upper air. The lows are caused by the air absorb- 

 ing heat from large areas of the earth's surface where the sun has 

 acted strongly. The heated air ascends and flows outward at the 

 upper levels, reducing the barometric pressure. If the air is moist. 



Fig. 4.— Showing the Okigins and Paths of Storms. 



when it rises under the action of heat, its pressure lessens until the 

 moisture is condensed; and the liberated latent heat serves further 

 to heat the air and increase the upward flow. The condensed mois- 

 ture usually appears as clouds or rain. 



The highs are found to enter the United States from only two 

 points. In the winter they usually originate in Alberta to the north 



