Storm Typing and Seedability in Orographic Snow/Rain Augmentation in the Sierra Nevada of California

Abstract

The seedability of winter-time storms depends on several meteorological criteria, three of the most important being storm size, temperature, and wind flow characteristics. A storm typing scheme was devised using readily available on-site radiosonde temperature and wind data. Data from several years of cloud seeding for snow pack enhancement in the Sierra Nevada of California indicate that moderate southerly storms predominated over moderate westerly systems in both seedable and seeded categories. The lack of seedabiIity was closely related to wind flow characteristics: high wind speeds associated with many of the westerly storms, and some of southerly cases, precluded targeting. Also important in seedability was the size of storm systems: many fast moving westerly cases bring only very small amounts of precipitation over a short period of time. Wind direction and air mass temperature were only third and fourth in importance in the lack of seedability.