SNOW AND EXPERIMENTAL METEOROLOGY 
this could develop into marked alterations of the general 
synoptic situation. Despite the skepticism of some mete- 
orologists, it seems reasonable to presume that such 
end results are quite likely, since this would be in 
Se a ae 
Fie. 14.—The effect produced in a supercooled stratus 
cloud with !4 pound per mile of dry ice. The straight legs of 
the pattern are 18 miles long. 
accord with the physical processes which lead to the 
formation of certain types of widespread natural storms. 
Figure 15 shows an area of cumulus clouds in New 
Mexico seeded with pellets of dry ice when the clouds 
were actively growing and had a vertical thickness above 
the supercooled layer of 5500 ft. The photograph illus- 
trates the appearance of the clouds 33 min after four 
_Fic. 15.—A view of the cloud area in New Mexico seeded 
with dry ice. The towering cumulus to the right of center was 
seeded with one pound of dry ice 15 min earlier. 
pounds of dry ice were placed in five local regions along 
the Monzano Mountains. Figure 16 shows the subse- 
quent development of the rainstorm triggered off by 
the dry-ice seeding. This cloud system produced its 
initial precipitation 15 min after dry-ice seeding was 
completed. The development of this storm was followed 
in minute detail by radar, two ground stations, and two 
airplanes. No other precipitation could be detected by 
the radar within sixty miles, and the precipitation 
231 
records show nothing within a hundred miles except 
from seeded clouds. An adjacent mountain range, the 
Sandia Mountains, to the northwest of the area used in 
these experiments, was employed as a control region. 
Although cumulus clouds similar to those which were 
seeded formed over the Sandias throughout the day, no 
Fic. 16.—Rain showers falling from cumulus cloud 90 
min after seeding with one pound of dry ice. 
trace of precipitation occurred from them. A series of 
experimental studies in July 1950 produced similar re- 
sults. 
The Effects of Silver Iodide Seeding. Anomalous cloud 
effects were anticipated and have been observed in 
regions where experiments were conducted with silver 
iodide. Figure 17 shows a large precipitation area which 
Fic. 17.—A rainstorm which originated in a region containing 
silver iodide produced by a ground generator. 
began in air filled with silver iodide particles and formed 
rain several hours before any other clouds developed 
in the region on July 21, 1949 near Albuquerque, 
New Mexico. Further information on this subject may 
be obtained from Langmuir’s and Vonnegut’s papers 
[13, 38]. 
Possibilities and Limitations in Seeding of Clouds 
In any science it is possible to establish the possi- 
bilities and limitations of certain physical phenomena. 
