MICROSTRUCTURE OF STORMS BY RADAR 91 
(l JULY 1958 
(615 EST 
boot _j 
Oo 10 20 MILES 
Fig. 4—Squall line 
tral Connecticut. There is a tendency for the 
lower end of the line to broaden and intensify im 
this region and to move relatively slowly so that 
the form and orientation of the line becomes al- 
tered as the northern end progresses more rapidly 
than the southern end. It is believed that the 
topography of each of these regions is conducive 
to the development of storms especially when the 
surface winds are more southerly than south- 
westerly, but the major characteristic of the pat- 
tern, the formation of a very narrow and intense 
line, must be dependent upon the larger scale 
circulation. 
SUMMARY 
Radar observations have shown that the rain 
associated with warm fronts is generally wide- 
spread but exceedingly variable in intensity. 
Moreover, the variations in intensity do not, at 
first glance, appear to form any easily recogniz- 
able patterns. However, the detailed study of 
storms in which the synoptic situation was very 
similar has shown that the small-scale rain pat- 
terns also exhibited a great deal of similarity. In 
particular, heavy rain appeared in areas 20-30 
mi in dimension, each of which contained a num- 
ber of smaller convective showers. These heavy 
rain areas appeared to develop in certain ‘pre- 
ferred’ regions at intervals of 45 min to one hour. 
They lasted for two or three hours and moved 
with the wind which was nearly constant between 
5000 and 18,000 ft. The individual showers, as 
defined by small closed contours, rarely lasted 
more than an hour. 
In the case of squall lines and cold-front bands 
the storms were grouped together because of the 
similarity of the rainfall pattern as depicted by 
the radar. The synoptic situations were also very 
similar except that some of the lines formed well 
ahead of the front and were called squall lines 
while two of them were in the immediate vicinity 
of the front. The latter two moved into the radar 
range as bands; in the case of squall lines, seat- 
tered showers occurred in the warm air ahead 
of the front and then became organized into a 
sharp line. The dimensions of the lines were over 
200 mi in length and usually less than 20 mi 
in width at the time of their greatest intensity 
and sharpness. They required a period of two 
to three hours for development and intensifica- 
