Wyoming Weather Modification Pilot Project

  • Overview
  • Background

Overview

The Wyoming Weather Modification Pilot Program (WWMPP) is funded by the State of Wyoming through the Wyoming Water Development Commission (WWDC), and is unique among state–sponsored programs in that it includes a substantial evaluation component. The main purposes of the WWMPP are to establish an orographic cloud seeding program in three target areas (the Medicine Bow Range, Sierra Madre Range and Wind River Range) and evaluate the feasibility and effectiveness of the cloud seeding. The logistics, infrastructure, and operations of the program are provided by Weather Modification Inc. (WMI), while the evaluation activities fall under the direction of the Research Applications Laboratory (RAL) of the National Center for Atmospheric Research (NCAR). A Technical Advisory Team, made up of representatives from several state and federal entities, has also been established to provide additional oversight and advice.

Clouds

Orographic clouds over the Medicine Bow Range, Wyoming.(©NCAR)

Background

Natural precipitation in winter storms develops and falls out when clouds:

  1. Contain supercooled liquid water (SLW), or at least water saturated conditions
  2. Exist in a temperature range for efficient ice nuclei (IN) activation and crystal growth
  3. Form in conditions conducive to snow development (collection of liquid cloud droplets – “riming”, or multiple ice crystals sticking together – “aggregation”)
  4. Have sufficient time for ice particles to develop, grow, and fall onto the barrier (or target area in this case)

Many storms are thought to be naturally inefficient in producing snowfall because they lack a sufficient number of IN active at the cloud temperatures where significant SLW is found. Such clouds may possibly be made more efficient by supplying additional IN in these regions of SLW; the essence of cloud seeding.

Attempts to increase snowpack by seeding clouds have been carried out for well over fifty years. Average increases of 10 to 15% have been reported in some experiments, but skepticism remains because many operational programs and scientific experiments have ended without conclusive results. Due to the large natural variability of precipitation and the relatively small seeding effect expected, it is generally believed that no single analysis can be convincing regarding the effect of seeding. Rather, it is necessary to build multiple layers of evidence, both statistical and physical, to provide a consistent picture of the effect of cloud seeding.

Evaluation of the WWMPP emphasizes the statistical analyses required to provide the evidence regarding cloud seeding efficacy. Nonetheless, the WWMPP also supports efforts to measure and model some of the physical effects of seeding, while remaining focused on a randomized statistical experiment. The overall goal of the WWMPP is to provide the best advice possible to the Wyoming Water Development Commission regarding the potential for meaningful augmentation of snowpack through cloud seeding.