CAUSES OF UNUSUAL WEATHER PERIODS 271 



FIG. 198. One cause of unusual seasons. Unusual paths of lows, March, 

 1910. Southerly winds over United States east of Rockies. Unusual tem- 

 perature over North-Central United States. 



FIG. 199. One cause of unusual seasons Remarkably cold weather, April, 

 1910. Paths of lows of that period. 



