Climatology and Ensemble Predictions of Nonconvective High Wind Events in the New York City Metropolitan Region

Abstract

amaging wind events not associated with severe convective storms or tropical cyclones can cause significant problems with transportation, infrastructure, and public safety over the northeastern United States. These nonconvective wind events (NCWEs) are difficult to forecast in New York City and surrounding regions as revealed by the relatively poor probability of detection (POD) and false alarm ratio (FAR) in recent years. This paper investigates the climatology of NCWEs between 15 September and 15 May over 13 cool seasons from 2000/01 through 2012/13. The events are separated into three distinct synoptic patterns: pre-cold-frontal (PRF), post-cold-frontal (POF), and nor?easter/coastal storm (NEC) cases. Relationships between observed winds and some atmospheric parameters such as 900-hPa geopotential height gradient, 3-h mean sea level pressure (MSLP) tendency, low-level wind profile, and stability are also presented. Overall, PRF and NEC have the largest FAR, because several events with a low-level jet at 1?2 km above the surface have relatively strong low-level stability that limits vertical momentum mixing. The POD is lowest for the POF events, which have a strong diurnal influence given the relatively deep mixed layer. Verification is also conducted over the cool seasons from 2009/10 to 2013/14 using the Short Range Ensemble Forecast (SREF) system from the National Centers for Environmental Prediction (NCEP). Both deterministic and probabilistic verification metrics are used to evaluate the performance of the ensemble during NCWEs. Although the SREF has more forecast skill than any of the deterministic SREF control members, it is rather poorly calibrated and exhibits a significant overconfidence given its positive wind speed bias in the lower troposphere.