SNOWIE – Seeded and Natural Orographic Wintertime clouds: the Idaho Experiment

Throughout the western U.S. and other semi-arid mountainous  region across the globe, water supplies are fed primarily through the melting of snowpack. Growing populations place higher demands on water while warmer winters and earlier springs reduce its supply. Water managers are tantalized by the prospect of cloud seeding as a way to increase winter snowfall thereby shifting the balance between water supply and demand. Little direct scientific  evidence exists that confirm even the basic physical hypothesis  upon which cloud seeding relies. The intent of glaciogenic seeding  of orographic clouds is to introduce aerosol into a cloud to alter  the nucleation of ice crystals, followed by ice particle growth to  sizes sufficiently large such that snow falls to the ground. Despite   numerous experiments spanning several decades, no direct observations of this process exist. 

Here, measurements from radars and  aircraft-mounted cloud physics probes are presented that together  show the initiation, growth, and fallout to the mountain surface of ice crystals resulting from glaciogenic seeding. These data, by  themselves, do not address the question of cloud seeding efficacy,  but rather form a critical set of observations necessary for such investigations. These are the first unambiguous observations of the physical chain of events following the introduction of glaciogenic cloud seeding aerosol into supercooled liquid orographic clouds.