HAILSTORMS 
IN THE 
DENVER NETWORK 351 
10 YRS 
ABS 0) 
60- 
- 
a 
= 
= 
jm 
MAME sd) od 
| HAIL DAYS BY MONTHS 
= 
N 
| 
1955 BAS eats | 
i eee | 
1957 
1958 | 
\ ' ' \ ' ' ‘ 7 | 
MAM J JS A S| O ON 
ae see ee 
Fic. 
4—Distribution of hail days by 
months; graph on left shows ten- 
year totals; figure on right is year-to-year distribution 
i) 
hi 
ois 
a 
n 
PERCENT OF REPORTS 
a 
rn 
nS 
ieee 
n 
ll 
9 10 WI 12 13 14 15 16 17 1B 19 20 21 ZemST ZZ0Im 
o8s9m 
Fre. 5—Time of hail onset based on ten years 
of data, 1949-1958; time of onset was determined 
for each hailstorm, or hailstorms identifiable as 
separate storms for each date 
Denver area, is an obvious feature of individual 
hailstorms crossing the network during weak 
hail years. During 1952, 1954, and 1956, years 
which were relatively inactive, hail-wise (see 
Table 1), patterns of fall were marked by spotty 
occurrences instead of well defined or extensive 
swaths. 
Synoptic and RAOB patterns—The 1956-1958 
performance of hailstorms in the Denver area 
bear out the facts summarized in our earlier 
study [Beckwith, 1956] as follows: 
(1) About half of the hail developments were 
associated with cold frontal passages within the 
previous 6 to 36 hrs. 
50 - 
40+ 
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WwW 
5) 
a 
WwW 
* 107 
GRAIN CURRANT PEA GRAPE WALNUT GOLF We 
APPROX A cs aM yy BALL ALL 
DIAMETER SYA; Vas v2 ¥o4 la 13/4" 21/2 
To 2" to 3" 
SIZE 
Fic. 6—Size distribution by frequency for larg- 
est hailstones reported at each observing point, 
829 reports over ten years 
(2) Wind direction on hail days at 500 mb 
favors WSW. 
(3) In only four per cent of the hail cases 
were cold lows found in or near Colorado. 
Crossings of jet streams within 100 mi of 
the network occurred on about 15% of the hail 
days. 
(5) Surface temperature just prior to onset 
of hail averaged 71°F. Values ranged for the ten 
years from 40° to 98°F, 
(6) The average surface dew point before pre- 
