342 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 60 



windows being on the west side of buildings. At Grand Island, the 

 storm caused major damage on the north side of the city with the 

 southern area having little diihculty. 



Although local reports suggested that the storm developed sud- 

 denly about 20 miles west of Grand Island, an examination of field 

 observations from several sources shows that a violent storm developed 

 in the broad trough in the lee of the front range of the Rocky Moun- 

 tains wdiich remained after a cold front passage on June 26. At 

 about 1300 on the 27th, large cumulus clouds began building 20 miles 

 west of Sterling, Colo. [1].^ These initially formed as single cells, 

 but by 1450 had moved eastward and merged mto an intense 80-mile 

 squall line stretching from Akron to Julesburg, Colo. At 1510, a 

 pilot, flying at about 12,000 feet east of Sterling, reported his AT-6 

 aircraft was showing 150 knots airspeed with the throttle closed. An 

 observer at Haxtun, Colo., reported roll clouds dropping to the ground 

 and back up to the cloud base at 12,000 feet within intervals of less 

 than a minute. Very little hail occurred in northeastern Colorado 

 with the exception of a zone of heavy hail damage 25 miles to the 

 west of Sterling. This occurred in the early afternoon. The wind at 

 Sterling, Colo., at ground level reached a maximum of 75 miles an 

 hour during the squall-line passage at about 1400. From the Haxtun- 

 Holyoke area, 26 farmers called the Sterling field station to report 

 the woret storm situation they had ever seen. If a line is drawn 

 from the zone north of Fort Morgan and west of Sterling, where 

 severe hail damage was reported early in the afternoon of the 27th, to 

 the area of heaviest damage which occurred at 2145 north of Grand 

 Island, Nebr., the distance is 250 miles, and the storm propagation at 

 ground level shows an average rate of movement of 28.5 m.p.h. The 

 direction of propagation closely coincides with the winds at 500 mb. 

 which showed a velocity of 40 to 45 knots during this period. 



During the period 2036 to 2242, very intense radar echoes from 

 the Grand Island area were observed at Schilling Air Force Base 

 near Salinas, Kans. Two strong echoes passed across the area where 

 the most severe hail damage occurred. The largest echo showed a 

 hooklike protuberance and coincided with the area of highest intensity 

 and damage. During the most intense hail period it had a diameter 

 of about 20 miles. 



This pair of echoes moved at a speed of about 45 m.p.h. with an 

 azunuth of about 255°. This was the wind velocity and direction 

 shown on a 500-mb. chart of 1800 c.s.t. Another radar unit at Offutt 

 Air Force Base near Omaha showed the same echoes and indicated 

 that this portion of the storm complex comprised the southern extrem- 

 ity of an extensive storm system, which by 2157 contained a line of 

 echoes over 100 miles long whose major axis was oriented with an 



* Numbers In brackets refer to list of references at end of article. 



