AEROLOGY OF EXTRATROPICAL DISTURBANCES 613 
500 
17 NOV. 1948 
1500 GMT 
120 
60.____@?_70, 
oR 
ye \ 
1500 GMT 
120 110 100 30 80 
((c) 
oat 
19 NOV. 1948 
| 1500 GMT 
120 
500 MB 
18 NOV. 1948 
0300 GMT 
500 MB 
19 NOV. 1948 
0300 GMT 
120 
Fria. 8. —Idealized 500-mb charts at 12-hourly intervals from 
1500 GMT November 17, 1948 to 1500 GMT November 19, 1948. 
Heavy lines, 500-mb fronts; thin lines, contours of 500-mb 
surface (labelled in hundreds of feet). Precipitation areas indi- 
cated by stippling in Fig. 8d. 
