WEATHER BUREAU. 167 



reports have proved of much value in accounting for the develop- 

 ment of disturbances in our Northwest. 



Summarized in a general way, a study of the international weather 

 map furnishes indications of weather conditions in the United States 

 several days in advance, somewhat as follows: 



(1) Barometer rising and above normal over the Asiatic high area; 

 barometer falling and below normal in the Bering Sea low area, and 

 rising over the Azores and falling over Iceland, indicates a period of 

 mild weather over the northern and eastern districts of the United 

 States. 



(2) Barometer falling and below normal over Bering Sea, antl 

 falling over the Azores and rising over Iceland, indicates a period of 

 cool weather generally east of the Rocky Mountains. 



(3) When the great continental high-pressure area extends over 

 west-central Europe and the British Isles it checks the movement of 

 North Atlantic storms and finally affects the rate of progression 

 of high and low pressure areas over the United States. The usual 

 rate of progression of liigli and low pressure areas over the United 

 States is resumed 5 or 6 days after a return to normal conditions 

 has set in over west-central Europe. 



(4) In its normal distribution atmospheric pressure is high over 

 the eastern and relatively low over the northern and northwestern 

 portions of Europe. Under these conditions the progression of 

 storms over the United States is normal. When, however, this 

 arrangement of pressure is reversed or disturbed, abnormal storm 

 movements or features will be observed. 



(5) At times when the air masses up over western Asia and con- 

 tinental Europe the advance of the Atlantic storms is checked, low 

 pressure prevails for se^ eral days over the British Isles, high pressure 

 Duilds up over the Atlantic Ocean, and the eastward progress of 

 high and low pressure areas over the United States is retarded. This 

 retardation or highs and lows over the United States is not inter- 

 rupted until about 5 or 6 days after normal pressure conditions arc 

 resumed over western Europe. 



(6) A slight shifting to the westward of the summer North Atlantic 

 high-pressure area gives temperatures above the normal and gen- 

 erally dry weather over eastern portions of the United States. If the 

 center of this high-pressure area shifts to the westward, south of its 

 usual position as regards latitude, the heat is general from the Gulf 

 of Mexico to Canada. If, however, the center occupies a more 

 northerly latitude in its westward position, the heat area is confined 

 to the more northerly districts of tlie United States, wliile the South 

 Atlantic districts receive the benefits of the easterly winds from the 

 ocean. 



(7) When the Atlantic high-pressure area occupies a position east 

 of its normal location over the Atlantic Ocean, or exhibits pressure 

 below normal, cool weather for the season, or at least variable tem- 

 perature, is experienced over the eastern portions of the United 

 States. 



(8) As a general proposition the North Atlantic high-pressures 

 area controls to a great degree not only the summer weather of tin- 

 greater part of the United States, but also the course and charactci 

 of the West Indian hurricanes. 



