Evaluation of the performance and distribution of hourly maximum fields from storm-scale ensemble forecasts

During the 2010 Spring Experiment held at the NOAA Hazardous Weather Testbed, the University of Oklahoma (OU) Center for Analysis and Prediction of Storms (CAPS) ran a 26-member storm-scale ensemble forecast (SSEF) system. With an abundance of high-resolution model data, it is difficult to determine in real-time the characteristics of the individual members. To address this issue, fields for which the temporal maxima are tracked over the previous hour (i.e., hourly maximum fields: simulated reflectivity, updraft helicity, updraft speed, downdraft speed, 10-m wind speed, and vertically integrated graupel) are investigated to assess the distribution and performance of the SSEF members in simulating storm attributes.

In this study, the distributions of hourly maximum fields of the SSEF members are examined over the experiment period to gain some understanding of the characteristics of the ensemble. For example, contributions to the ensemble maximum fields are ascertained for individual members and subsets of members with initial condition or physics perturbations. In addition, the general performance characteristics of individual members and subsets of members in forecasting severe weather are evaluated based on the magnitude of hourly maximum fields in the vicinity of observed storm reports. Overall, a better understanding of the distribution and performance characteristics of the SSEF system will aid in interpretation and configuration of future convection-allowing ensemble systems.