Abstract
The complex terrain at the intersection of the Mohawk and Hudson valleys of New York has an impact on the development and evolution of severe convection in the region. Specifically, previous research has concluded that terrain-channeled flow in the Mohawk and Hudson valleys likely contributes to increased low-level wind shear and instability in the valleys during severe weather events such as the historic 31 May 1998 event that produced a strong (F3) tornado in Mechanicville, New York. The goal of this study is to further examine the impact of terrain channeling on severe convection by analyzing a high-resolution WRF Model simulation of the 31 May 1998 event. Results from the simulation suggest that terrain-channeled flow resulted in the localized formation of an enhanced low-level moisture gradient, resembling a dryline, at the intersection of the Mohawk and Hudson valleys. East of this boundary, the environment was characterized by stronger low-level wind shear and greater low-level moisture and instability, increasing tornadogenesis potential. A simulated supercell intensified after crossing the boundary, as the larger instability and streamwise vorticity of the low-level inflow was ingested into the supercell updraft. These results suggest that terrain can have a key role in producing mesoscale inhomogeneities that impact the evolution of severe convection. Recognition of these terrain-induced boundaries may help in anticipating where the risk of severe weather may be locally enhanced.
Significance Statement
On 31 May 1998, a widespread tornado outbreak occurred in the northeastern United States. One damaging tornado during the outbreak impacted the city of Mechanicville, New York. We used a high-resolution computer model simulation to examine how the topography of the region near Mechanicville affected the potential for tornado occurrence. We found that the topography contributed to the formation of an atmospheric boundary west of Mechanicville at the intersection of the Mohawk and Hudson valleys. The region to the east of the boundary was characterized as an environment particularly favorable for tornadoes. These results suggest that the identification of similar boundaries may be useful in increasing situational awareness of where the risk of severe weather may be locally enhanced.
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