Examining Terrain Effects on Upstate New York Tornado Events Utilizing High-Resolution Model Simulations

The region at the intersection of the Mohawk and Hudson Valleys of New York is characterized by complex terrain, which is hypothesized to have an impact on the development and evolution of severe convection in the region. Previous research has hypothesized that terrain-channeled flow in the Hudson and Mohawk Valleys has contributed to increased low-level wind shear and instability in the valleys during past severe weather outbreaks. However, a lack of observations in the region prevented this hypothesis from being robustly tested.

The goal of this study is to further examine this hypothesis and complement existing observations by utilizing the Weather Research and Forecasting (WRF) model. High-resolution simulations were developed for two tornado cases. The first case occurred on 31 May 1998, when a strong (F3) tornado struck Mechanicville, New York as part of a widespread severe weather outbreak. The second case occurred on 29 May 2013 and featured a strong (EF2) tornado in the mouth of the Mohawk Valley. WRF model simulations from both cases suggest that terrain-channeled flow resulted in an environment particularly favorable for severe weather where the tornadoes occurred. On 31 May 1998, terrain-channeled flow resulted in the formation of a robust moisture gradient at the intersection of the Mohawk and Hudson Valleys. East of this boundary, the environment was characterized by extreme low-level wind shear, and enhanced low-level moisture and instability, supporting tornadogenesis. On 29 May 2013, results also suggest terrain-channeled flow enhanced wind shear and moisture in the region where the tornado occurred. However, the role of terrain is more uncertain in this case and research is ongoing to better understand the complexities of both events.

Results from both cases suggest that terrain can drive mesoscale inhomogeneities that impact the evolution of severe convection. However, there remains a forecast challenge in anticipating the significance of terrain ahead of a particular severe weather event. Identifying additional cases when terrain played an important role may be useful in improving the prediction of severe weather events in upstate New York.