MICROSTRUCTURE OF STORMS BY RADAR 89 
POSITION OF 
BAND AT 
2100 EST, 
Fre. 3—Regions and times of development of rain areas, November 8-9, 1957 
termine the details of the upper air wind field at 
a particular time and place and to make a closer 
comparison with the motions of the rain areas. 
The large band itself seemed to drift in an 
easterly direction at a speed slightly less than 
half that of the individual rain areas. 
Durations of rain areas—In each of the storms 
the main band retained its identity as a band for 
a period of about three hours. Then the pattern 
broke up and became rather disorganized but 
showed a tendency to form smaller bands as il- 
lustrated in Figure 2. The areas of heavy rain 
within the band and the general area into which 
it evolved were estimated to have a lifetime of 
about three hours. Most of them were observed 
on the contour maps for only 11% to 21% hours. 
Extrapolations beyond the range of the SCR- 
615-B radar were based on photographs of the 
AN/CPS-9 scope and the hourly rainfall records. 
A number of ‘individual showers’ as defined by 
small closed contour lines were tracked and their 
durations observed. Most of those which could 
be tracked easily lasted between 20 and 50 min 
with a few enduring for over an hour, usually the 
more intense ones. There were also many small 
areas, especially of light rain, which lasted 15 min 
or less and were not included in the survey. 
Development of rain areas—Because of the 
limitations imposed by the range of detectability 
of the radars many of the regions of development 
cannot be determined with certainty. However, 
whether the rain areas actually developed at or 
near their estimated positions of origin or whether 
they moved into radar range at those locations, 
some very interesting recurrences are observed. 
Figure 3 shows the estimated times and appear- 
ances of ten of the heavy rainfall areas in the 
storm of November 8-9, 1957. They seem to ap- 
