Winter Weather

Investigating Precipitation Formation in Winter Storms

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Water resources in the western U.S. primarily comes from winter snowpack. .In response to increasing demand and limits on supplies, western communities have instituted water-conservation measures to preserve existing supply and/or sought additional water sources through technologies such as cloud seeding. Water will become an increasingly scarce resource as the population continues to grow and the climate changes over the coming decades (Rasmussen et al. 2011). Reduction of water supplies impacts nearly all aspects of western U.S. society, including drinking water, hydropower, irrigation, and tourism.  The recent report by the U.S. Bureau of Reclamation (20xx) highlights these western water issues, and also outlines approaches to further conserve and develop water in the west, including the use of cloud seeding. 

It is not surprising then that many western states have sought to augment water using operational cloud seeding programs.  These programs are based on glaciogenic cloud seeding with either silver iodide (AgI) or liquid propane.  The concept is that some wintertime clouds contain liquid water at subfreezing temperatures, or supercooled liquid water (SLW), that has not participated in the precipitation process due to the lack of effective ice nuclei at relatively warm subfreezing temperatures (typically -5 to -15 C).  Cloud seeding can provide artificial ice nuclei that can convert these supercooled liquid drops to ice crystals that rapidly grow to snowflake sizes and fall out.  

To date, the effectiveness of glaciogenic cloud seeding with AgI has not been scientifically verified.  HAP scientists have been requested by various state entities to perform a scientifica evaluation of the potential for orographic seeding.  This has led to active work in Wyoming and Idaho.  

Measuring snow

Solid precipitation (i.e. snow, ice) is one of the more complex parameters to be observed and measured by automatic sensors. The measurement of precipitation has been the subject of numerous studies, but there has limited coordinated assessments of the ability and reliability of automatic sensors to accurately measure solid precipitation. The WMO Solid Precipitation Measurement Intercomparison Experiment (SPICE) focuses on measuring precipitation amount, precipitation intensity, and precipitation type (liquid, solid, mixed), over various time periods (minutes, hours, days, season) as well as snow on the ground (snow depth).

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Winter Weather