The Use and Interpretation of Numerical Weather Prediction Model Output in Identifying Synoptic-Scale Environments Associated with Development of Mesoscale Convective Systems

Abstract

An experiment is reported in which derived diagnostic parameters computed from Limited-area Fine-Mesh (LFM) model gridpoint data were examined to determine subjectively whether their availability in real time would assist the forecaster in interpreting and understanding the model's forecast of the weather. Specifically, model products thought to relate to the development of mesoscale convective weather systems (MCSs) were combined into a composite forecast and compared with the standard ensemble of LFM products for 25 episodes of significant convective activity. An objective verification of the LFM forecasts themselves was not attempted. Both 12 and 24 h forecasts from the 1200 UTC run were considered. In a majority of cases, it was evident that derived diagnostic gridpoint data added information about parameter patterns and values important to MCS development that was not obvious from viewing the conventional model products alone. Two case studies demonstrate how information about 850 mb moisture convergence and lower tropospheric temperature advection can help to understand why the model predicted a maximum in vertical velocity (and precipitation) in a region that did not look favorable for large-scale ascent as diagnosed from the conventional output.