Hailstorm Structure Viewed from 32,000 Feet 
Rosert M. CunNINGHAM 
Aerophysics Laboratory, Geophysics Research Directorate, Air Force Cambridge 
Research Center, Bedford, Massachusetts 
Abstract—Photographs taken near Cheyenne, Wyoming, on a high-altitude flight 
from the cloud-studies aircraft of AFCRC show hail thrown out of the side of a large 
organized thunderstorm. A small vortex is visible at one edge of the hail shaft. The re- 
lation of the hail region to other regions of the cloud is clearly evident. The cloud and 
hail patterns, revealed after mapping the clouds from the photographs, suggest a hori- 
zontal cyclonic circulation of the whole storm. 
While studying the effects of local topography 
on the cloud patterns east of the Denver area, 
aerial photographs were taken of a well-de- 
veloped large hailstorm. This paper will discuss 
these photographs and the measurements made 
from them. 
On the afternoon of September 11, 1958, the 
AFCRC C-130 Hercules aircraft, equipped with 
cloud-probing and large mapping cameras (T- 
1l’s) flew along a SSE-NNW line some 80 mi 
east of the Front Range of the Rockies. Small 
showers and thunderstorms had produced a gen- 
eral chaotic cloud mass over the Rockies. Figure 
1 shows the tops of these clouds as they descend 
and evaporate in the westerhes flowing down 
from the mountains. The photograph was taken 
looking toward the west. A west-east lne of 
cumulus is visible at a lower altitude. These 
mountain thunderstorms have not developed into 
self-propagating storms; presumably at least 
on this day they cannot survive passage through 
the downdraft region east of the Front Range. 
In contrast to the poorly organized thunder- 
storms over the mountains, large well organized 
hailstorms were photographed east of our flight 
path (Figs. 2 and 3). These storms were self- 
propagating, lasting until after midnight. Moun- 
tain wake circulations may be of importance 
here; that is, the large storms first develop in 
and under a region of general upward motion in 
the first downstream wave beyond the mountain. 
Once started over flat terrain, these storms, on 
drifting eastward, can apparently become or- 
ganized enough to outweigh the effects of the 
farther downstream portion of the mountain 
wave. 
The surface and upper-air conditions can be 
described as follows. A thin layer of moist hot 
air was moving at moderate velocity from the 
325 
south and southeast over the region just east 
and north of Denver and Cheyenne. Tempera- 
tures reached into the upper eighties (all surface 
readings in °F) in this region and dew points 
were recorded at Akron, Colorado, in the lower 
fifties, and at Scotts Bluff, Nebraska m the lower 
sixties. The surface air at Denver, however, was 
part of the direct flow down off the mountains 
as the dew point fell in the afternoon to the 
upper thirties, the temperature reached the up- 
per eighties, the wind was light and variable. 
Cheyenne recorded light southeast winds with 
surface temperatures in the lower eighties, dew 
points near fifty. The vertical thermal and wind 
structure of the atmosphere is shown on a skew 
T, log P diagram, (Fig. 4). The features to note 
are the following: (1) The thinness of the sur- 
face layer of southeast wind with slowly increas- 
ing westerly wind above, and the strong west 
northwest winds above the isothermal layer at 
33,000 to 35,000 ft. (2) The difference in the 
moisture structure over Denver and over Scotts 
Bluff; the air at Denver below 23,000 ft is 
relatively homogeneous with a nearly constant 
potential temperature and small range in mois- 
ture content, suggesting again that this air is well 
mixed and comes from the higher terrain to the 
west. The air at Scotts Bluff, on the other hand, 
is moist in the lower layers and very dry above 
15,000 ft. (3) The isothermal layers, a minor one 
at 22,000 ft, a major one at 33,000 to 35,000 ft. 
This latter layer is perhaps a remnant of a more 
northerly tropopause. The sharp tropical tropo- 
pause appears at 51,000 ft. 
The hailstorms to be discussed were, it ap- 
pears, surrounded by an atmosphere close to that 
measured by the Scotts Bluff radiosonde. The 
maximum temperatures during the day in the 
storm area reached as high as 91°F (33°C). A 
