An Extratropical Cyclone Categorization Using Atmospheric River Moisture Flux Applied to Western Canada

Abstract:

A new extratropical cyclone scale is proposed to help identify major storms in western Canada for public safety applications. This scale builds upon the atmospheric river scale which is tracked using integrated vapor transport and precipitation (rate and amount). This effort aims to identify in advance the potential severity of major storms to support operational forecasting and warnings and prevent harmful impacts. Our focus is on southwestern British Columbia in western Canada, to respond to concerns that global warming is expected to have increased precipitation and more severe storms, and may cause potentially more impacts on infrastructure and public safety. Although this Extratropical Cyclone/Atmospheric River scale was designed for southwestern British Columbia, it shows promise for categorizing impactful storms across Canada. The most impactful storms in Western Canada (and in mid- and northern latitudes) are associated with intense streams of atmospheric moisture that tap into tropical convection. Results show that the larger and more intense the storm the greater the stream of moisture that feeds into it. Such category 4 or 5 “Super Storms” may occur only 1% of the time currently but may be the most harmful. These major storms are the most important to forecast well in advance, and there is a pressing and growing need to prevent their damaging impacts. In this paper, the Canadian ARkSuperStorm effort is introduced using case studies to demonstrate how storms may be classified to better address their impacts (from beneficial to harmful). Trend analyses are used to address concerns that global warming will generate more extreme weather across western Canada with more harmful impacts. This research provides a useful scale to help improve warning preparedness in western Canada for significant storms and to help address global warming concerns