166 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



While the bulletin is devoted principnllj'^ to the work of Weather 

 Bureau officials at the observatory, its columns are open to eminent 

 scientists throughout the world. Among the latter who have con- 

 tributed during the year are Prof. II, S. Woodward, president of the 

 Carnegie Institution of AVashington; Prof. A. Lawrence Kotch, direc- 

 tor of the Blue Hill Observatory ; E. Gold, of the meteorological office 

 of London ; and Prof. J. H. Jeans, of Princeton University. 



FORECASTS AND WARNINGS. 

 UPPER-AIR OBSERVATIONS AS AIDS TO FORECASTING. 



The daily telegraphic reports of upper-air observations from Mount 

 Weather, Va., have been of aid to the forecaster at Washington dur- 

 ing the past year, and it is believed that their continued use will 

 further increase the accuracy and range of the forecasts. The follow- 

 ing are concrete exami^les of possibilities in this way : 



In this section a storm center sometimes passes eastward or north- 

 eastward over the ocean, without being followed by clearing weather 

 on the coast States, as would ordinarily be expected, because of a 

 secondary storm development off the middle or south Atlantic coast. 

 A study of the Mount Weather kite flights shows that north winds 

 occur at high altitudes in advance of the formation of a storm of this 

 character. Thus, it is hoped to be able in future to forecast their 

 development, and thereb}' increase the accuracy of the forecasts of 

 the weather that follows for the entire coast district. 



Again, it has been found that when a low-pressure area is approach- 

 ing from the southwest, and the winds turn to the right (clockwise) 

 with ascent, the usual warming up in the Atlantic States seems to be 

 retarded about twenty-four hours. 



Also, the turning of the winds to the left (counter-clockwise) with 

 increased altitude shows the depth of the cold northwest wind. From 

 this may be drawn reasonably correct inferences as to the fall in tem- 

 perature that may be expected at the surface of the ground within the 

 next twenty-four hours. 



The thickness of the stratum of cold air that advances from the 

 west or northwest with the approach of an anticyclonic area is of the 

 highest importance in determining subsequent temperature conditions. 

 The temperature reports for high altitudes show whether the stratum 

 is shallow or of great depth. When shallow, the cold weather accom- 

 panying the high is neither severe nor of long duration ; but if the 

 blanket is thick and abnormally low temperatures are reported aloft, 

 the cold will be of marked intensity and will probably last several 

 days. In predictions of sleet, also, it is essential to know what is 

 going on in the upper air. Conditions favorable for sleet are com- 

 paratively Avarm upper air and a thin laj^er of lower air with its tem- 

 perature somewhat below the freezing point. 



HURRICANES OF THE YEAR. 



The hurricane season of the past year was marked by a number of 

 severe tropical disturbances. AYarnings were given to shipping and 

 other interests in every instance in time for them to take all necessary 

 precautions. 



The Galveston hurricane of July 21^ 1909. — The storm Avas first 

 observed in the Caribbean Sea to the southeast and then to the south 



