Extreme Freezing Rain Events in the Province of New Brunswick, Canada, and their Evolution in the Future Using Convection-Permitting Simulations

Abstract:

Several ice storms can occur in Atlantic Canada and can cause significant impacts on many sectors of society. For example, in January 2017 a major ice storm resulted in a major power outages in the province of New Brunswick, Canada after up to 50 mm of freezing rain fell during three days. We examined the conditions leading to extreme freezing rain accumulation in New Brunswick (NB) and its changes in the future. To be able to well represent meso-scale features within storms and the local effects on precipitation distribution, we used high-resolution convection-permitting simulations of the Weather Research and Forecasting model (WRF) at 4 km grid spacing over the continental US (Liu et al., 2017). The control simulation, which was produced for the period 2000-2013, included 7 extreme freezing rain events (>12.5 mm) that resulted in major power outages in NB. A simulation was also conducted in Pseudo Global Warming Mode (PGW), simulating the 2000-2013 weather patterns in a future climate, isolating the thermodynamic response of climate change on weather events.

Our analysis showed that extreme freezing rain accumulation in NB results typically from strong extra-tropical cyclones that form over southeastern US and travel toward Atlantic Canada. Also, the low-level wind field during individual freezing rain events showed that the presence of the Appalachian Mountains in NB enhances the differential temperature advection associated with veering winds through the process of cold air damming. This favors the development of strong temperature inversion in the lower-levels, which leads to an increase of freezing rain amounts in central NB. In the PGW climate projection, there is a major decrease of freezing rain event occurrence in the coastal regions of NB (southern and eastern NB), while it increases in northwestern NB, especially for long events (>6 hours). Overall, this study contributes to a better understanding of meteorological factors leading extreme freezing rain amounts in NB and to better anticipate the impact of climate change on those storms.