An examination of tornado environments, events, and impacts from 2003-2012

The NOAA NWS Storm Prediction Center (SPC) has created a database of environmental parameters associated with observed severe convection, based on archived SPC hourly mesoscale analysis grids. The database includes severe weather parameter estimates for each severe report since 2003 (264 211 reports; 14 032 tornadoes), an archive of all SPC forecast products, and access to gridded US lightning data. Using this database, the characteristics of tornado environments in parameter space (i.e. CAPE-Shear, CAPE-SRH, etc.) are examined with particular attention paid to major tornado events.

Regional and seasonal differences in tornado environments are documented and placed in the larger context of the potential societal impact of tornado events. For equal tornado threat, events that occur over densely populated areas of the country are likely to have greater societal impact than events over less populated areas. Thus, in densely populated areas such as parts of the Southeast, Ohio Valley, and Atlantic coast, storms in relatively less favorable tornado environments (such as those characterized by low CAPE and moderate/strong wind shear) may still pose a significant risk to life and property, while storms in very favorable environments will pose a particular risk of major impact, such as the event of 27 April 2011.

Finally, SPC watch verification as a function of storm environment is analyzed in order to isolate environments where forecast skill can potentially be improved. While forecast performance is generally very good in environments that are highly favorable or highly unfavorable, events that occur in more commonly observed marginally favorable environments still pose a major forecast challenge in terms of both probability of detection and false alarm.