Tornadoes within weak CAPE environments across the continental United States

Given the well-established importance of buoyancy in conjunction with vertical shear for severe convective storms, tornadoes occurring within weak buoyancy regimes can pose unique challenges to operational forecasters. A preliminary climatology of tornadoes estimated to have occurred with weak buoyancy, as defined by Mixed-Layer (ML) CAPE of 500 J/kg or less, is presented for the continental United States for 2003-2009. Estimated MLCAPE values were derived from a 40 km gridded dataset of the Storm Prediction Center's hourly Mesoscale Analysis archive, which is based on a blend of surface METAR observations and RUC analysis fields. The comprehensive SPC relational database of severe events and environmental data contains more than 2500 tornadoes that have occurred with MLCAPE < 500 J/kg. Seasonal, temporal, geographic, EF-scale climatologies are presented, in addition to relational examination of these events to common convective indices and general synoptic/mesoscale patterns. A number of prior research studies have identified common scenarios for tornadoes within weak CAPE regimes (i.e. tropical systems, "cold core" mid-latitude closed lows, low-topped California storms, Gulf Coast cool season), but this study may help further document the frequency of occurrence with such patterns.