Environmental Control of the Inland and Orographic Enhancement of Lake-Effect Precipitation over the Tug Hill Plateau

The factors controlling intra- and inter-storm variations in the inland and orographic enhancement of lake-effect precipitation remain poorly understood, yet identifying these factors is critical to accurate precipitation forecasting in many lake-effect-prone regions. The focus of this study is the Tug Hill Plateau of upstate New York, site of the Ontario Winter Lake-Effect Systems (OWLeS) field program. The plateau rises gradually to a modest 500m above Lake Ontario and features significant enhancement of precipitation during many lake-effect periods. OWLeS was conducted from Dec 2013 – Jan 2014, and the orographic component of the project sought to document and better understand the inland and orographic enhancement of lake-effect snowfall over the plateau. Several mechanisms for this enhancement have been explored using OWLeS data, and this work seeks to continue that investigation.

Analysis of data from the entire OWLeS period, as well as 13 years of lake-effect periods identified by Veals and Steenburgh (2015), suggest that some key factors controlling enhancement include the strength of the cross barrier flow (i.e., the mean 975–850 hPa zonal wind speed) and the lake-induced low-level instability (evaluated using the difference between the mean lake surface temperature and the 850 hPa temperature). Higher wind speeds produce greater inland penetration of precipitation and more persistent precipitation over the plateau. In contrast, during weak flow, precipitation is largely confined to the lower slopes and near the lake shore. Low instability values favor a confinement of echoes to the plateau and inland areas, while high values favor areas closer to the shore and over the lake.

These results, along with ongoing analysis of the influence of lake-effect mode, capping inversion height, and other factors, help illustrate the mechanisms controlling the distribution of lake-effect precipitation in areas of complex terrain, with important implications for operational weather forecasting.