The impacts of the PNA and NAO on annual maximum snowpack over southern Canada during 1979–2009

The Pacific/North American pattern (PNA) and North Atlantic Oscillation (NAO) are two of the most important atmospheric low‐frequency variability modes modulating interannual anomalies of snowpacks in North America. However, the quantitative degree to which the PNA and NAO affect the annual maximum snow water equivalent (SWEmax), a quantity directly relevant to the ground snow load calculation in National Building Code of Canada, remains unknown. This study explores the relationship of the winter PNA and NAO to the Canadian SWEmax anomalies and potential changes associated with atmospheric circulation patterns. Significant correlations are identified in eastern and western Canada, where climatological mean values are largest due to the high frequency of snow storm occurrence. The regions in Canada where SWEmax anomalies are influenced by the PNA and NAO experienced a significant change from pre‐1998 to post‐1998. This change is consistent with the observed changes in annual maximum snow depth and the winter atmospheric circulations during 1979–2009. Copyright © 2012 Royal Meteorological Society