Case Study of )-6h Experimental and Operational Forecasts

The atmospheric science community generally agrees that probabilities are a meaningful method for forecasting convection because they allow the quantification of uncertainty. In addition, probabilities provide a methodology (or common unit) to combine observational-based forecasts with Numerical Weather Prediction (NWP) and forecaster input. National Convective Weather Forecast – 2 (NCWF-2) provides short-range (1 and 2hr) probabilistic nowcast of convection based on radar, lightning and RUC data. The NCWF-2 is intended to be a preliminary step toward a continuous 0-6 hr probabilistic forecast. These data are currently provided to the forecasters at the National Weather Service (NWS) Aviation Weather Center. This paper uses case-studies from the summer to evaluate NCWF-2 strengths and weaknesses.

The NCWF-2 forecasts combine traditional radar extrapolation techniques with the use of RUC data to capture storm growth and large-scale storm trends. The use of the RUC data and its effects on the NCWF-2 probabilities are examined. The radar data are used to identify a set of cases based on the organization of the convection and its stage of evolution. For each case, synoptic pattern characteristics, proximity soundings, dominant forcing mechanisms, and thermodynamic properties are evaluated. The current NCWF-2 forecasts are evaluated to find systematic strengths and weaknesses. The utility of each RUC predictor field used for determining the NCWF-2 convection likelihood is assessed. These results lend insight into characteristics of convection not well resolved by the NCWF-2 algorithm and indicate model parameter thresholds used by the NCWF-2 that may need modification.