SURFACE ANALYSIS IN TERMS OF No 197 



As a representative example of the application of these newly developed 

 units to a synoptic situation, a large-scale outbreak of continental polar 

 air which took place over the United States during February 1952 is 

 analyzed in terms of A^o and A [42, 43]. 



For this synoptic illustration the reduced expression, No, is used in 

 preparing constant level charts of the storm at the same levels and times 

 as those used in the daily weather map series of the U.S. Weather Bureau. 

 The A unit, on the other hand, is employed to construct vertical cross- 

 sections through the frontal system to give a three-dimensional picture of 

 the synoptic changes taking place. 



5.5. Surface Analysis in Terms of N^ 



A pronounced cold front developed and moved rapidly across the 

 United States during the period 18 to 21 February 1952. 



Prior to February 18, a polar maritime air mass had been moving slowly 

 eastward across the Great Basin and Rocky Mountain regions. This 

 system included a slow-moving cold front extending from northern Utah 

 southwards into Arizona and a quasi-stationary front extending north- 

 eastwards into Wyoming. With the outbreak of polar continental air 

 east of the Rocky Mountains, the maritime front became more active 

 and, as it moved ahead of the fast-moving polar continental front sweep- 

 ing across the Great Plains, was reported as a squall line by the time it 

 crossed the Mississippi River early on the morning of February 20. 

 During the latter stages of the storm system, the polar maritime cold 

 front-squall line was located in the developing warm sector of the polar 

 front wave. The entire ensemble of cold front, polar front wave, and 

 squall line then moved rapidly to the east coast by the morning of the 

 21st, thus completing the sequence. 



Charts of Ao were prepared from Weather Bureau surface observations 

 taken at 12-hour intervals from 0130 EST, February 18 until 0130 EST, 

 February 21, 1952, or, in other words, the period of time that it took the 

 polar front wave to develop and move across the country. The synoptic 

 sequence is seen on figures 5.19 through 5.25., where contours of A^o are 

 derived for various stages of the storm and compared to the superimposed 

 Weather Bureau frontal analysis. The same procedure of comparing 

 derived contours with the existing frontal pattern was followed throughout 

 the present example. Observations from 62 weather stations were used 

 in preparing the surface weather maps. Figure 5.19 indicates that the 

 cold front extending from Utah southward displays weak A^o changes 

 across the frontal interface. In the early stages of the sequence (figs. 

 5.19 and 5.20) this lack of air mass contrast is evidenced in another way 

 by the slight change of the position of the Ao = 290 contour encircling 

 west Texas and New Mexico as the frontal system moves through that 

 area. 



