DISCUSSION 69 
TaBLE 2—Cloudburst rainfall in the United States 
| 
Vertical moisture 
Remarks 
Location Date Lapse rate 
Franconia, Va. | Sep. 1, 1952 Unstable 
Thrall, Texas Sep. 9-10, 1921 | Unstable 
Hallett, Okla. | Sep. 4, 1940 | Unstable | 
| 
Chicago, Il. Oct. 9-19, 1954 | Unstable 
Surface to 550 mb 
Surface to 500 mb 
| = : 
Tornadoes associated with hurri- 
cane Able 
Surface to 700 mb | Record 19.65 inches in 12 hr in two 
bursts (remnants of Gulf hurri- 
cane) 
Surface to 300 mb | 15.5 inches in 9 hr., non-frontal air 
| mass 
6.72 inches in 9 hr., record, all thun- 
derstorm rain, south of warm 
front 
The Hallett storm occurred as an air-mass type 
in very moist, conditionally unstable air. It is 
noteworthy that the rain fell between 02h00m 
and 11h00m CST which signifies that this was < 
nocturnal storm which had been growing, per- 
haps, from the previous afternoon and thus must 
have built into an enormous-sized single thunder- 
storm. It, too, qualifies as an example satisfying 
the conditions for runaway convection. The 
Franconia storm was similar to the Thrall storm 
in that it was associated with the remnants of a 
dying hurricane low center. Although no record 
rains accompanied this storm, it was notable for 
the tornadoes it spawned. 
The Chicago storms are additional examples of 
the conditions resulting in runaway convection. 
Here one had low-level convergence, high mois- 
ture, and conditionally unstable air south of a 
warm front so that it was possible to have small 
but intense updraft areas and widely distributed 
downdraft areas [JZeans, 1956]. 
Following this line of argument, one may in- 
quire into the possibilities for the creation of 
intense, self-sustaining, local storms through ar- 
tificial means. One feature which must be present 
is the large areal inflow to and outflow from the 
storm. In addition, high moisture, at least in the 
inflowing air, should be present. Nature provides 
ready-made situations of this type in the vicinity 
of low-pressure areas and one would need only to 
intensify certain updraft regions to set off run- 
away convection since the other elements for a 
self-sustaining storm are present already. One 
would expect to find the most favorable oppor- 
tunity in a warm sector where moist tropical air 
is present with appreciable sunshine. Under these 
conditions, it seems favorable to encourage the 
growth of large Cumulus congestus clouds by dust- 
ing smaller Cumuli with solar energy converting 
materials such as carbon black. The dusting 
should be done so as to create a larger flow field 
by merging several adjacent Cumuli. This seems 
to be the way nature accomplishes the formation 
of thunderstorms and we might well begin by 
trying to imitate her. 
REFERENCES 
Beers, N., Atmospheric stability and instability, 
Handbook of Meteorology (F. A. Berry and 
others, ed.), pp. 693-725, McGraw-Hill, 1945. 
Evrassen, A., ann E. Kiernscumipt, Dynamic 
meteorology, Encyclopedia of Physics (S. Flugge, 
ed.), 48, Geophysics II, Springer-Verlag, Berlin, 
pp. 1-154, 1957. 
H6ruanp, E., On the interpretation and applica- 
tion of the circulation theorems of V. Bjerknes, 
Arch. Math. Og Naturv. vol. 42, 68 pp., 1939. 
Lor, G. A., The unparalleled Thrall, Texas, rain- 
storm. Mon. Wea. Rev., 81, 195-203, 1953a. 
Lorr, G. A., An extraordinary rainfall centered 
at Hallett, Oklahoma, Mon. Wea. Rev., 81, 1-10, 
1953b. 
Means, L. L., Some basic parameters associated 
with the flood rains at Chicago, Oct. 9-12, 1954, 
Mon. Wea. Rev., 84, 253-260, 1956. 
PETTERSSEN, 8., Weather analysis and forecasting, 
2nd ed., vol. 2, McGraw-Hill, 266 pp., 1956. 
VONNEGUT, BERNARD, CHARLES B. Moore, AND 
ALEXANDER T. Borka, Preliminary results 
of an experiment to determine initial precedence 
of organized electrification and precipitation in 
thunderstorms, J. Geophys. Res., 64, 347-357, 
1959. 
Discussion 
Mr. Douglas K. Lilly—lVd like to propose an- 
other possible interpretation of the evidently pe- 
riodic characteristics of those observations. It 
seems that there must be some instability in order 
