Short-Range (0–48 h) Numerical Prediction of Convective Occurrence, Mode, and Location

Abstract

A verification of high-resolution (6-km grid spacing) short-range (0–48 h) numerical model forecasts of warm-season convective occurrence, mode, and location was conducted over the Lake Michigan region. All available days from 5 April through 20 September 1999 were evaluated using 0.5° base reflectivity and accumulated precipitation products from the national radar network and the day-1 (0–24 h) and day-2 (24–48 h) forecasts from a quasi-operational version of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5). Contingency measures show forecast skill for convective occurrence is high, with day-1 (day 2) equitable threat scores and Kuipers skill scores (KSS) of 0.69 (0.60) and 0.84 (0.75), respectively. Forecast skill in predicting convective mode (defined as linear, multicellular, or isolated) is also high, with KSS of 0.91 (0.86) for day 1 (day 2). Median timing errors for convective initiation/dissipation were within 2.5 h for all modes of convection at both forecast ranges. Forecasts of the areal coverage of the 24-h accumulated precipitation in convective events exhibited skill comparable to the lower-resolution, operational models, with median threat scores at day 1 (day 2) of 0.21 (0.24). When small displacements (less than 85 km) in the precipitation pattern were taken into account, threat scores increased to as high as 0.44 for the most organized convective modes. The implications of these results for the use of mesoscale models in operational forecasting are discussed.