H. A. Hazen— Tornadoes. 189 
der-storms? How are they connected with each other and 
what is their movement? What wind directions preyail? 
What is the distribution of temperature? Is their relation to 
storm-centers an invariable one? What is the character and 
distribution of hail storms? and soon. Asa partial answer to 
the last question, observation seems to establish a rule that hail 
storms occur only in immediate proximity to storm-centers of 
considerable energy. 
__ In order to be able to predict violent local storms and torna- 
does we can accomplish much, as has just been suggested, by a 
study of a map containing the weather conditions over a large 
region. 
Some of the signs of probable tornado action may be enumer- 
ated, in conclusion, as follows: 
trst—There must be a storm-center fairly well marked, 
though this may be 600 or 700 miles away. Tornadoes almost 
invariably occur to the south and southeast of this point. 
cond—It is believed that the temperatures in the above 
region should be above the mean. Great contrasts of tempera- 
ture are not necessary, and if, in connection with these, an area 
-of high pressure is found to the northwest or west, no tornado 
will ordinarily occur. 
trd—In general the air should be moist. 
