Lake-Effect Mode and Precipitation Enhancement over the Tug Hill Plateau during OWLeS IOP2b

Orography has a dramatic influence on lake-, sea-, and ocean-effect storms (hereafter simply lake effect). The Tug Hill Plateau of northern New York (hereafter Tug Hill) rises 500 m above the eastern shore of Lake Ontario and experiences some of the most intense snowstorms in the world. In this presentation, we investigate the enhancement of lake-effect snowfall over Tug Hill during IOP2b of the Ontario Winter Lake-effect Storms (OWLeS) field campaign. During the 24-h study period, total liquid precipitation equivalent along the axis of maximum precipitation increased from 33.5 mm at a lowland (145 m MSL) site to 62.5 mm at an upland (385 m MSL) site, the latter yielding 101.5 cm of snow. However, the ratio of upland to lowland precipitation, or orographic ratio, varied with the mode of lake-effect precipitation. Strongly organized long-lake-axis parallel bands, some of which formed in association with the approach or passage of upper-level short-wave troughs, produced the highest precipitation rates but the smallest orographic ratios. Within these bands, radar echoes were deepest and strongest over Lake Ontario and the coastal lowlands and decreased in depth and median intensity over Tug Hill. In contrast, non-banded broad coverage periods exhibited the smallest precipitation rates and the largest orographic ratios, the latter reflecting an increase in the coverage and frequency of radar echoes over Tug Hill. Numerical simulations by the Weather Research and Forecasting model highlight the orographic and non-orographic mechanisms responsible for the overall precipitation distribution and enhancement over Tug Hill. Findings based on this work should aid operational forecasts and, given the predominance of broad coverage lake-effect periods during the cool season, help explain the climatological snowfall maximum found over the Tug Hill Plateau.