WEATHER MAPS 301 



5. Predictions are sometimes based on imperfect data. On some 

 weather maps the letter M appears in various places. This means 



that reports from the station where the M appears are missing. If 

 many reports are missing, the map is imperfect, but the forecaster 

 must use such data as he has, as well as he may, and issue a map. 



6. In some situations storms are subject to many freaks. This 

 is the case, for example, at Chicago, where the lake modifies tem- 

 perature and air currents. 



Forecasters, like other men, make mistakes, but when they 

 have to work with so many uncertain elements, it is not strange 

 that their predictions are sometimes wrong, and one mistake is 

 likely to be remembered longer than many correct forecasts. 



Property saved by predictions of storms, frosts, floods, etc. 

 In spite of all mistakes, the warnings of storms, floods, cold waves, 

 etc., sent out by the Weather Bureau, have been of great benefit. 

 The value of this service is not always duly appreciated, and much 

 less is heard of it than would have been heard of the losses which 

 would have resulted if warnings had not been given. Unfortu- 

 nately, it is not always possible to devise protection against the 

 evils of which the Weather Bureau gives warning. 



It has been estimated that property valued at $15,000,000 was 

 saved in 1897 by warnings of impending floods. In 1903-4 the 

 estimated saving was $1,000,000. 



Shipping interests are served by warnings of storms. Thus, in 

 September, 1903, vessels valued at $585,000 were held in ports 

 temporarily, along the coast of Florida, by storm warnings. 



Agricultural interests are also served by warnings of storms 

 and of "cold waves," and especially of frosts. Warnings led to the 

 protection of $1,000,000 worth of fruit about Jacksonville, Florida, 

 in 1901, with an estimated saving of half this amount. Other 

 warnings of cold in 1901 were estimated to have been the means 

 of saving more than $3,000,000 worth of property. Fruit and truck 

 farming are the phases of agricultural work most effectively served 

 in this way. 



Special Types of Storms 



Thunder-storms. Thunder-storms are frequent in the United 

 States. They are most common in warm regions, and in warm 



