On the Usage of SPC Slight Risk Convective Outlooks to Identify Cases with Low Predictive Skill

This study provides an objective evaluation of severe convection predictability using Storm Prediction Center (SPC) convective outlooks as well as a method to identify severe weather events with low-predictive skill. Initial case studies of select events, such as the 4 May 2010 and 18 January 2012 cases, suggest highly sheared environments with reduced buoyancy can be particularly challenging. The database consists of 0600 UTC SPC outlooks for the 24-hour period beginning at 1200 UTC to 1200 UTC the next day. Slight risk areas are projected on a 40 x 40 km grid across both the continental U.S. and northeastern U.S. domains to evaluate the predictability of severe weather over the Northeast region relative to the predictability over the continental U.S. as a whole. Using hail, wind, and tornado reports valid for the forecast period, probability of detection, false alarm ratio, and critical success index verification metrics are calculated for a 13-year period from 2000-2013. Difficult cases with a low critical success index are segregated into categories having a false alarm ratio of at least one standard deviation and/or a probability of detection of lower than one negative standard deviation. 500 hPa flow patterns, convective available potential energy, and vertical wind shear are examined for each low predictability scenario. Preliminary results using cases from 2009-2013 indicate that the Northeast region has higher predictability than the continental US.