Topographic and boundary influences on the 22 May 2014 Duanesburg, New York, tornadic supercell

The 22 May 2014 Duanesburg, New York, supercell produced an enhanced Fujita scale category 3 (EF3) tornado and 10-cm-diameter hail. The synoptic setup for the event was ambiguous compared to other documented cases of Northeast tornadoes. Mesoscale inhomogeneities due to terrain and baroclinic boundaries played a key role in the evolution and severity of the storm. The storm initiated at the intersection of an outflow boundary and a north-south-oriented baroclinic boundary. The mesocyclone was able to sustain itself as a result of sufficiently large amounts of low-level streamwise vorticity near the boundary despite subcritical values of 0-6-km vertical wind shear. Differential heating across the north-south-oriented boundary strengthened the pressure gradient across it. Strengthening ageostrophic flow across the boundary induced greater upslope flow along the southeastern slope of the Adirondack Mountains and induced terrain channeling up the Mohawk River valley. The channeling led to a maximum in moisture flux convergence and instability in the Mohawk valley. As the supercell moved into the Mohawk valley, radar and lightning data indicated a rapid intensification of the storm. Cold temperatures aloft due to the presence of an elevated mixed layer (EML) coincided with the surface instability to yield a local environment in the Mohawk valley favorable for extremely large hail. As the storm crossed the boundary, large values of 0-1-km wind shear, streamwise vorticity, and low lifting condensation levels combined to create a local environment favorable for tornadogenesis.