tions in middle or northerly latitudes. It represents a rather stable type of weather 

 in the higher latitudes. Consequently it is of less direct concern than is the second 

 type to the synoptic meteorologist, who is concerned principally with the forecast- 

 ing of unusual or severe conditions, or the sudden change of conditions. 



The second low index type is the usual active winter type which is charac- 

 terized by the formation of large polar anticyclones at the higher latitudes, princi- 

 pally over the continents. Cyclonic activity increases at the lower latitudes. The 

 principal frontal systems take either a north-south orientation, or an east-west 

 orientation at low latitudes. The individual cyclones, which may be quite intense, 

 follow corresponding tracks. Either they move northward, skirting the western 

 edge of a major continental anticyclone that blocks eastward movement in the 

 higher latitudes, or they move eastward across the continents at low latitudes, 

 skirting the southern edge of the polar continental anticyclones. 



Especially over western Europe and the eastern Atlantic does the onset of 

 this active winter weak circulation pattern tend to follow a characteristic line of 

 development. An extensive polar anticyclone from the interior of Asia pushes 

 westward over northern Europe to the North Atlantic. The Icelandic low tends 

 to be weakened and displaced westward over southern Greenland. Usually a 

 secondary center develops in the vicinity of the Bay of Biscay from which active 

 lows pass southeastward into the Mediterranean. Northern and central Europe 

 are dominated by the strong westward flow of extremely cold polar continental air 

 from the interior of Asia. Blizzard conditions occur in western Europe wherever 

 strong cyclonic activity in the south leads to marked frontal action along the 

 southern edge of the cold air mass. Most remarkable is the strength of the west- 

 ward thrust of the continental anticyclone in northern Europe, and its ability to 

 resist the eastward advance of strong lows in the western Atlantic. It is this par- 

 ticular blocking action of the polar anticyclone which most frequently leads to 

 serious forecast errors along the northwest coast of Europe, forecasts of storms 

 which fail to make their influence felt where they are expected. This blocking action 

 in the north terminates only when the polar anticyclone begins to weaken or to 

 move southward. Similar conditions on a somewhat smaller scale occur occasion- 

 ally along the west coast of North America when a weak circulation pattern is 

 established in the Pacific, with an intense Polar continental anticyclone extending 

 southeastward from Alaska. The Aleutian low is displaced far to the west, with a 

 secondary cell located off the California coast, whence a succession of lows pass 

 eastward along the southern border of the United States, causing heavy rains in 

 southern California and heavy snows in the southern plateau and southern Rockies. 



In terms of the circulation pattern over the /Atlantic and western Europe 

 the period from January 9-24, 1933, falls into three parts. Between January 9 

 and January 15 the pattern is fairly typical of strong circulation over the Atlantic. 

 Lows in rapid sequence deepen and move rapidly northeastward to the Greenland- 

 Iceland region, where the Icelandic low reaches its maximum intensity on January 

 14. Southerly storm conditions with mild temperatures (cf. Figure 8) are recurrent 

 along the northwest coast of Europe. However, it will be noted that the maximum 

 storm activity even during this period is centered rather far west over the Atlantic, 

 so that only the extreme northwest coast of Europe is strongly affected. At the 

 same time it will be noted that in the interior of Europe a weak circulation pattern 

 is already in evidence. This is indicated by persistent abnormally high pressure 

 over western Russia and abnormally low pressure in the central Mediterranean Sea 

 (cf. Figure 1). Thus a cold anticyclonic circulation of polar continental air from 



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