Figure 26. Normal weather chart for November (U.S. Weather Bureau, 1952). The 

 solid lines show the pattern of sea-level air pressures (millibars), and the thin solid 

 arrows mark the flow of winds near the earth's surface. The weather for the whole of 

 November, of course, does not remain stable on a day-to-day basis, there being a regu- 

 lar progression of migratory lows from the northwest to the southeast across the con- 

 tinent. Behind each mobile low there follows a ridge of high pressure, usually starting 

 just east of the Canadian Rocky Mountains (see the weather map for November 7, 

 1947, on page 105). The tracks of these high-pressure cells flow almost exclusively from 

 the northwest to the southeast, as shown by the heavy black arrows (Berry, Owens, and 

 Wilson, 1952). The broken lines and arrows indicate the contour and wind flow at the 

 700 millibar surface (approximately 10,000 feet above sea level). At this height, where 

 weather is less under the influence of surface variations, the predominance of Novem- 

 ber's northwesterly movement of wind over the whole of North America becomes more 

 apparent. 



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