An Analysis of the Predictability of the February 2021 Cold Air Outbreak at S2S Timescales

The February 2021 cold air outbreak (CAO) brought long-lasting, freezing temperatures and winter weather to the United States and Canada. The event resulted in major societal and economic impacts, including millions of power outages and approximately $25 billion in losses. This case study first analyzes the synoptic evolution of this event in order to explain how Arctic air arrived and stalled over central North America. Given the synoptic context, the analysis next considers the subseasonal-to-seasonal predictability of this CAO by examining S2S ensemble model predictions from both high-top and low-top models. The S2S predictability analysis is motivated by the idea that processes in the stratosphere, such as sudden stratospheric warmings (SSWs) and wave reflection events, can play a significant role in CAOs. Due to this, high-top and low-top forecast data will be compared to determine if models that better resolve the stratosphere were able to predict the high impact nature of this event with longer lead times.