Synoptic and meteorological conditions during extreme snow cover ablation events in the Great Lakes Basin

Abstract

AbstractSnow cover ablation in the Great Lakes basin is a common and hydrologically important process during the cold season, contributing to a majority of the basin's runoff, and less frequent, extreme ablation events are highly impactful due to an increased flooding risk and warrant specific investigation. A brief climatology of extreme ablation events is presented, where extreme is considered within the top 5% of the distribution. Using synoptic classification techniques, individual weather patterns associated with extreme snow ablation in the Great Lakes basin are isolated. A single pattern deemed the most influential in generating extreme ablation events, southerly flow‐1, is examined in detail, and three case studies are presented to determine the meteorological conditions and surface energy fluxes responsible for ablation. Over 75% of extreme events are associated with southerly flow patterns that predominantly ablate snow with sensible heat fluxes, while rain‐on‐snow patterns induce the remaining extreme events from 1980–2009. Type southerly flow‐1 is responsible for 45% of the extreme events and is characterized by strong southerly advection of warm air into the basin, where sensible heat fluxes of 45–125 Wm−2 are responsible for the majority of energy transfer into the snowpack. When compared with an average ablation event, an extreme ablation event for southerly flow‐1 exhibits air temperatures, dew point temperatures, and wind speeds that are 3.8°C, 3.0°C, and 1.2 ms−1 warmer and faster than an average event, indicating a greater potential for larger ablation.