Two mesoscale numerical weather prediction models, Eta and the Rapid Update Cycle (RUC), are currently being run operationally at the U.S. National Weather Service's National Meteorological Center to produce nationwide weather forecasts. Improvements in weather forecast accuracy depend on increasing model resolution, which is limited by available computing resources. Massively Parallel Processing (MPP) offers a cost-effective way of increasing computing resources. At the Forecast Systems Laboratory, we are developing parallel versions of both models that can be easily ported between different MPP systems and traditional sequential machines. To support this effort, we have developed the Nearest Neighbor Tool (NNT), a software library of...