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7—Size distribution by months of largest hailstones reported at 
Denver during period 1949-1958 and at Alberta during 1957-1958 (by 
Douglas) 
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NUMBER OF CASES 
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I6- 20- 24- 28- 32- 36- 40- 44- 48- 52- 56- 60- 
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oF 
Fre. 8—Surface dew-point frequency distribu- 
tion at Denver during ten-year period; dew point 
is the value measured at official U. 8S. Weather 
Bureau station prior to onset of precipitation of 
any type 
cipitation began was 46°F. (Figure 8 gives the 
dew-point distribution for the ten-year period.) 
One of the most obvious differences in char- 
acteristics between hailstorms of the High Plains 
and those of the Middle West is in comparing 
the surface dew-point distributions in the two 
regions. Denver dew points above 55°F are 
rarely measured prior to hailstorms. In contrast, 
Fawbush and Miller [1953] pomt up the fact 
that surface dew points for Middle West storms 
are nearly always in the 60’s and 70’s. 
A preliminary survey of the Denver RAOBs 
for 18 hail days selected at random during 1956, 
1957, and 1958, shows a temperature and mois- 
ture relationship in the vertical as illustrated in 
the mean sounding of Figure 9 and in the data 
below: 
Freezing level: 590 mb 
Wet bulb freezing level: 637 mb 
Temperature at LCL: 5°C 
(lifting condensation level) : 
Tropopause height: 134 mb* 
* Approximately 45,000 ft 
In comparing these figures with the mean hail- 
storm soundings computed by Fawbush and 
Miller [1953], a similarity is found from 700 mb 
to 400 mb for stone diameters between one and 
two inches. The greatest discrepancy lies in the 
5000-ft layer above the surface. The High Plains 
moisture distribution is marked by a low hu- 
midity at the surface, increasing gradually to 
about 500 mb and decreasing gradually above 
this level. The inversion above the moist layer 
noted by them as a pattern for stones of one inch 
diameter or larger is also missing in the mean 
Denver sounding. However, the 0°C wet-bulb 
temperature is reached at about 7500 ft above 
the terrain, again in agreement with a consistent 
parameter for the larger stones. Extending the 
