HAILSTORMS AND HAILSTONES — SCHAEFER 347 



moisture invasion channeled into the area from the Gulf of Mexico, 

 and the role played by the mountains in removing the low-level moist 

 air from the west but favoring the overrunning of the warm gulf air 

 from the SSE. by cool, moist air aloft advected by a strong NNW. 

 straight-line flow. When this occurs, there is often a relatively dry 

 layer in between that favors the development of intense storms. She 

 points out that cyclogenesis readily develops in the leeside trough 

 formed by the mountains when a slow-moving cold front moves across 

 northeastern Colorado. The frontal waves emerging from this re- 

 action move along the cold front, which slowly drifts to the northeast, 

 and tend to develop violent squall lines at the interface. She points 

 out that the June 27, 1959, storm considered here is a typical example 

 of this type of synoptic pattern. This type of mesoscale system favors 

 the formation of a few giant cells that may exceed vertical heights of 

 60,000 feet. 



Further studies in this region will better establish the relationship 

 of the lee waves of the Jetstream produced by Sierra Blanca, Mount 

 Evans, Long's Peak, and Laramie Peak, as well as their orographic 

 effects. These particular mountains are often observed to form cloud 

 streets and a triggering effect on convective activity, wdiich is then 

 reinforced in the lee trough mentioned by Easley. It is also possible 

 that the normally low concentrations of nuclei for ice-crystal forma- 

 tion that characterize this area may play an important role in the hail 

 formation so commonly observed in the area. 



5. NEED FOR MORE CLOUD-SEEDING RESEARCH IN THIS REGION 



Cloud-seeding efforts to modify or prevent hail have been centered 

 in the past in the vicinity of Scotts Bluff, Nebr., and Sterling, Colo. 

 Tliis is probably a good location for affecting cumulonimbus, which 

 develop locally. It is likely that a more effective teclmique for modi- 

 fying large storms such as described in this paper requires the intro- 

 duction of high concentrations of nuclei in the tongues of low-level 

 moisture moving up from the Gulf of Mexico. The large, intense 

 storms of this area develop so rapidly there is hardly time to spread 

 adequately the silver iodide nuclei to prevent the development of large 

 hailstones. Further efforts among research scientists, commercial 

 cloud-seeding organizations, and farmers' groups need to be encour- 

 aged if further progress in understanding these severe storms is likely 

 to be achieved. 



Over the next few years many basic studies should be actively pur- 

 sued in the Sterling- Scotts Bluff area of Colorado and Nebraska. A 

 detailed mesoscale analysis should be made of particular storms, 

 including photographic records from the air and ground, detailed 

 studies of the hailstones produced, measurement of ice and condensa- 



