Vol 13-2 2018

On 1 March 2016, an EF2 tornado occurred near Birmingham, AL, and was examined as part of VORTEX-SE.  The boundary-layer environment near the tornadic supercell was heterogeneous in space and unsteady in time, with what typically would be considered an excellent proximity sounding.  In this case, however, the proximity sounding severely underestimated the CAPE. SPC mesoanalyses substantially underestimated the CAPE and wind shear as well.  Tornadogenesis occurred near a weak, frontogenetical thermal boundary, where evaporation from antecedent light showers had also increased dewpoint values.  A local maximum in surface dewpoint (and instability), and a local maximum in helicity both existed near the region of frontogenesis.  As a QLCS moved into the region of higher CAPE air, part of it became supercellular.  Tornadogenesis occurred near the local maximum in surface dewpoint.