The efficacy of cloud seeding in enhancing snowfall has been investigated in the last 60 years, in particular glaciogenic seeding of clouds over mountains. The results of previous campaigns have been unconvincing mainly because of the challenge of distinguishing the effects of seeding from natural variability, which is significant. The most recent large project is the Wyoming Weather Modification Project (WWMPP), which uses silver iodide (AgI) generators over the Medicine Bow range, and other mountains in Wyoming.
WRF-based cloud-resolving larger eddy simulations (LES) are used to simulate ground-based AgI dispersion and its impact on orographic clouds and precipitation. The simulations are couched in the context of WWMPP-supported seeding and measurements. They stand out because of their extremely fine resolution, down to 100 m.
The first step regards the dispersion of AgI nuclei released from point sources on the ground on a clear day, over the Medicine Bow range. Airborne IN counter measurements are used to evaluate the simulations. Next, profiling airborne radar data are used to validate numerical simulations of the impact of ground-based glaciogenic cloud seeding on microphysical processes in a shallow orographic winter storm. This work shows that under suitable conditions AgI cloud seeding does increase snowfall, but it also confirms the above-mentioned challenge that changes in storm intensity can easily overwhelm the seeding effect.