A Comprehensive 5-year Severe Storm Environment Climatology for the Continental United States

Analysis of the environments associated with severe convection provides key insights into the character and predictability of these storms. To this end, the NWS Storm Prediction Center (SPC) has created a database of environmental parameters associated with observed severe convection since 2003 (138,136 reports; 7224 tornadoes), based on archived SPC hourly mesoscale analysis grids. The database also includes an archive of all SPC forecast products and gridded US lightning. Using this comprehensive database, we assess the total or conditional risk of severe weather as a function of environmental parameters (i.e. in “CAPE-Shear” space) or other dimensions of the database. Spatial distributions of the seasonal, annual, or 5-year frequency of key severe weather environments are also be explored.

Calculations of the conditional probability of severe weather as a function of environmental space illuminate the higher probability of thunderstorms and conditional probability (given lightning) of tornadoes for large mixed-layer CAPE (MLCAPE > 1000 Jkg-1) and strong shear (0-6 km Shear > 40 kt). However, because of the more common occurrence of environments characterized by MLCAPE less than 1000 Jkg-1, over 48 percent of all tornadoes within the five year sample including 39 percent of EF2-EF5 tornadoes occur in these low CAPE environments. Environments supportive of tornadoes, damaging winds and large hail will be contrasted for both severe and significant severe events. Substantial inter annual variability in severe storm environments and reports is documented and the contribution of major outbreak events to the severe weather environment climatology is explored. Finally, preliminary results from research to isolate severe reports and environments associated with specific storm types such as supercells will be presented.