1998 is the third consecutive year that the Oklahoma Water Resources Board has contracted with Weather Modification Inc. (WMI) to conduct the Oklahoma Weather Modification Demonstration Program (OKWMDP). The OKWMDP is an operational program with the dual purposes of precipitation enhancement and hail suppression using cloud seeding aircraft. During all three years the OKWMDP has been evaluated by the Environmental Verification and Analysis Center (EVAC) at the University of Oklahoma. The main difficulty in evaluating a weather modification program is the highly localized nature of convective events. An additional complication with evaluating an operational program is that seeding is performed with little or no randomization. Thus, it is difficult to establish control groups and experimental groups for comparison.
EVAC has several tools to overcome these limitations. The Oklahoma Mesonet is a network of 114 automated environmental observation stations located throughout the state. The USDA Agricultural Research Service maintains the Micronet, which consists of 45 automated sites within the Washita River watershed in southwest Oklahoma. In addition to these surface observation networks, Oklahoma has extensive weather radar coverage. There are four WSR-88D radar sites within the state, and nine of the surrounding sites have portions of Oklahoma within their coverage volumes. TITAN (Thunderstorm Identification, Tracking, Analysis and Nowcasting) is a radar data visualization and analysis software package developed at NCAR and will be used to analyze the WSR-88D data.
Two strategies will be used in the OKWMDP evaluation: verification of results (on the ground) and verification of effects (on the seeded cells). For verification of results, Mesonet/Micronet rainfall data and WSR-88D precipitation estimates can be used in conjunction with climatological data and seeding aircraft position data to generate a comparison of rainfall in seeded and non-seeded areas. For verification of effects, TITAN has the ability to identify and track cells and provide a quantitative analysis of those cells. When combined with seeding aircraft position data it is possible to identify seeded cells and compare their development with natural cells.