90 PAULINE M. AUSTIN 
pear in certain preferred regions at approxi- 
mately hourly intervals. A similar recurrence was 
observed in the storm of October 18-19, 1957. 
Five rain areas appeared in northern Massachu- 
setts along the Connecticut River valley, between 
the hours of 23h30m and 02h15m EST, with in- 
tervals between the appearances of 45 min to one 
hour. Two heavy-rain areas appeared in the vi- 
cinity of Hartford, Connecticut, at 22h45m and 
23h30m EST respectively and moved along the 
same path about 80 mi apart. 
Sufficient data have not been analyzed to per- 
mit one to assess the respective roles of local 
topography and larger seale storm dynamics in 
determining the preferred regions and recurrence 
intervals for the development of such rain areas. 
However, the fact that areas of heavy rain move 
along at 45-65 mi/hr and persist for periods of 
two to three hours suggests that local topography 
is not the sole factor in producing the observed 
patterns. 
SeuaLL Lines AND Coup-FrRontT Banps 
General description of storms—During the 
summer of 1958 intensity contour data were 
taken on six squall lmes or sharp cold-front 
bands. A study was initiated to investigate the 
development of these bands and, in particular, 
to determine the extent of the similarity in pat- 
tern details for the different storms. All except 
one had the characteristic that for a period of 
several hours they consisted of a long narrow 
line of intense convective cells. The one exception 
showed two lines, neither of which was as long or 
narrow as those associated with the other storms. 
All of the lines were either ahead or in the vi- 
cinity of a cold front and exhibited strong con- 
vective activity, although none would have been 
classified as a severe squall line. As in the case of 
warm-front storms, the data from two radars and 
the hourly rainfall records are being combined to 
reconstruct the details of the storm as well as 
possible. The analysis of these storms has not 
been completed and only a few preliminary re- 
sults can be presented here. 
Spatial dimensions—The observed length of 
the lines at the time of their greatest mtensity 
and sharpness appeared to be limited by the radar 
range. Hence it may be concluded that they ex- 
tended for at least 200 mi. The width of each line 
was about 20 mi, at least an order of magnitude 
smaller than the length. Individual convective 
showers whose dimensions were on the order of 
five to ten miles were spaced irregularly along 
the line about 20 to 50 mi apart. A typical pat- 
tern is shown in Figure 4. The approximate rain- 
fall rates for each intensity level in Figure 4 are 
as follows: 
Level tL 23 4s 
Rainfall rate (mm/hr) 5 10 25 45 75 
Time scales—The development of the line from 
the time it first appeared as a line (that is, a few 
scattered showers but definitely lined up) to the 
time of its maximum intensity and sharpness re- 
quired two to three hours. For another two or 
three hours the line persisted and then it began 
to dissipate. Lifetimes of individual showers, as 
defined by small closed contours, varied from 
about 15 min to nearly three hours, but the rela- 
tively intense ones usually lasted about an hour. 
Since the order of magnitude of the time scales 
involved is the point of interest in this discussion 
and since the definition of ‘showers’ is dependent 
ina rather arbitrary manner upon the resolution, 
both in space and intensity, of the instrument, 
the observations on shower duration are pre- 
sented as a qualitative estimate rather than a 
statistical survey. 
Development of rain areas—The development 
or intensification of the line itself usually took 
place between 12h00m and 15h00m EST, ap- 
parently reflecting the effect of diurnal heating, 
although in one case maximum intensity was 
reached as late as 1ShOOm EST. Individual storms 
sometimes developed within the lne and ocea- 
sionally ahead or behind it but, in general, there 
appeared to be several ‘preferred’ regions for 
shower development. One of these areas was along 
the Hudson River; on at least two days storms 
developed there throughout the early afternoon. 
They appeared on the southern end of the line 
so that the area of development moved southward 
along the river valley as the line progressed. In 
all of the storms the orientation of the line was 
approximately northeast-southwest and the in- 
dividual showers moved toward the east-north- 
east. For some of the storms we have not yet 
analyzed the AN/CPS-9 data and therefore do 
not know whether development occurred along 
the Hudson Valley. A second region where many 
showers developed was in the mountains of New 
Hampshire just east of the Connecticut River 
valley. On three days showers were occurring 
more or less randomly in that area for several 
hours before the line formed, and on occasion the 
line itself seemed to intensify as it passed over 
the region. A third area of development is in cen- 
