The changing nature of ablation-inducing synoptic weather types in the North American Great Lakes basin

Abstract

The runoff generated by snow cover ablation dominates regional hydrology in the North American Great Lakes basin, while rapid events can represent a physical hazard due to flooding. In determining the likelihood and magnitude of an ablation event, both the presence of snow cover and the synoptic-scale atmospheric environment should be considered, where the atmospheric environment provides the meteorological characteristics and surface energy fluxes necessary for ablation. Pending snowpack availability, variations or changes in the frequency of ablation-inducing synoptic types, and/or varying suitability of meteorological characteristics for snowmelt, can alter the frequency of ablation events. In light of a changing global climate, it is unclear if and how ablation-inducing synoptic types in the Great Lakes basin have transformed in recent decades as from 1960 to 2009, the interannual frequency of snow cover ablation events in the Great Lakes basin has significantly decreased. This study uses synoptic classification as a mechanism for identifying ablation-inducing synoptic weather types and for determining if changes to the frequency and inherent meteorological characteristic of the type are occurring. For a majority of the ten most impactful ablation-inducing synoptic weather types examined, significant trends are noted in their interannual frequencies, which can be partially explained by variations and trends in the phases of common teleconnection indices, such as the North Atlantic and Arctic Oscillations. Collectively, inherent meteorological characteristics of particular weather types in the basin are becoming more suitable for ablation, with increases in surface air temperatures, more southerly wind flow, and less cloud cover, plus increases in liquid precipitation rates during rain-on-snow synoptic types. Independent of snow cover, atmospheric environments suitable for ablation are becoming more frequent and generally more favorable for ablation.