An article written in collaboration with:
Jessica Vial, Climate Scientist
During the winter of 2022-2023, North America experienced harsh weather conditions with dangerously low temperatures. Some of the notable events that occurred during this period include:
– From December 21 to 26, 2022, a snowstorm and cold air surge affected most of the United States and parts of Canada, resulting in over 100 casualties.
– Between January 31 and February 2, 2023, a winter storm brought heavy snow and ice across the southern United States.
– From February 2 to 3, 2023, a brief but intense cold snap hit eastern Canada and northeastern United States, leading to record-breaking low temperatures.
Among these events, the December storm named Elliott was the most destructive
More than 70% of the US population was affected by warnings that included blizzards, high winds, heavy snowfall, and record cold temperatures (1). This “once-in-a-generation storm” had the greatest impact in the Buffalo area (in the New-York state), with over 50 casualties and a city completely paralyzed for several days. Insurance market losses for damage to residential, commercial and industrial properties and automobiles are estimated at $5.4 billion across 42 US states (2).
Like most winter weather of this type, storm Elliott also caused power outages and disruptions to road, rail and air traffic, making it difficult to provide emergency assistance to individuals in need. In additions, severe winter weather is a major cause of disruption to many organizations, both public and private, with consequences on business interruption and supply chain disturbances.
Figure 1: (Top) Surface air temperature at 2 meters on December 23, 2022 at 12 UTC. The red rectangle over Central United States is the area used for the time series in the bottom panel. (Bottom) Evolution of daily mean temperature at 2 meters in December 2022 (black line), as compared to the interquartile range (in grey) computed for all Decembers from 1960 to 2020. (Data source: ERA5 Copernicus (3)).
How did winter storm Elliott occur?
Every time there is an extreme cold wave in the United States, Russia or Europe, the term “polar vortex” comes up.
What is it?
It is a band of strong westerly winds that circulate in the stratosphere (between about 15 and 50 km) above the poles in winter, keeping the extremely cold air locked in over the Arctic in the northern hemisphere (Figure 2). However, the polar vortex is a fairly unstable phenomenon, and as it weakens it can cause rapid descents of cold air into the mid-latitudes (4).
It was around Christmas that extremely rapid drops in temperatures were observed in the United States, as low as -31°C in Denver (Colorado) or more surprisingly -9°C in Houston (Texas) (5). At the same time, very mild temperatures prevailed in Western Europe. These two simultaneous temperature excesses on both sides of the Atlantic Ocean are often characteristic of these large meanders of the upper-level westerly winds (called the jet streams).
But, that’s not all…
This descent of cold Arctic air came into conflict with a mass of warm air from the Gulf of Mexico, giving rise to a “bomb cyclone”. This term is used when the pressure – of a low-pressure system in formation – drops by more than 20 hectopascals (hPa) in 24 hours. In the case of the storm Elliott, the pressure dropped by 40 hPa in twenty-four hours (5).
The Great Lakes region, on the northeast border of the United States and Canada, is also prone to what is known as “lake effect” snow.
This occurs when cold, dry arctic air passes over a large area of unfrozen water, picking up moisture that is then dumped as snow when it reaches lakeside areas. In Buffalo, 56 cm of snow in 24 hours was recorded, largely beating the old record of 32 cm from 1976 (6).
This is how freezing temperatures combined with a blizzard and heavy snowfall for several days can quickly turn the dream of a white Christmas into a nightmare, as Buffalo residents experienced.
Figure 2 : Polar vortex and the arctic air mass (UCAR).
Does global warming have anything to do with it?
Although the impact of global warming on many types of extreme weather events is becoming increasingly clear (for hot extremes, droughts, heavy precipitation), when it comes to extreme winter weather, there is much less scientific evidence.
One theory in particular is being debated : the influence of warming Arctic temperatures on the polar vortex leading to extreme cold events over mid-latitudes (7). Some scientists support the idea that because the Arctic warms faster than other regions (three to five times faster), the temperature difference between the pole and the tropics is decreasing, leading to a weaker polar vortex and a greater likelihood of cold air outbreak, as in the case of the December 2022 event.
But while it is clear that the Arctic has warmed more than the global rate over the past 50 years, the influence on the strength and waviness of the high-altitude polar winds is often criticized for the lack of statistical significance and the inability to disentangle the role of climate change and natural climate variability.
Moreover, according to the latest IPCC assessment, it is virtually certain (99 to 100% probability) that the frequency and intensity of cold extremes have declined globally since 1950, and there is no reason to believe that the tendency will reverse in the future (8).
It is worth noting that global warming plays a role in the amount of precipitation (9): warmer air can hold more moisture, increasing the water reservoir of a thunderstorm or low-pressure system. This means that the same weather system can unleash much more precipitation in a warmer world. This is why rainfall is becoming more extreme in many parts of the world.
Figure 3: Winter storm sweeping across the US Midwest on December 23, 2022 (NOAA)
Similarly, in winter, more snow can fall (rather than rain).
That said, as the winters are getting warmer precipitation might be more likely to fall as rain, rather than snow in the future (9), reducing the winter snowpack that in many areas disrupts access to transportation, as well as energy and water supplies.
How can companies prepare to sever winter events?
Although winters are getting warmer, cold snaps, snowstorms and strong winds are not going to stop happening anytime soon. The first step is to quantify the potential impacts of extreme weather on the supply chain, on networks (water, energy, communication and transport) and physical assets themselves using robust climate data and scientific assessment.
The second step is to design a continuity plan that will help ensure employee safety, increase companies’ resilience to these events by maintaining essential functions, limit some of the damages or losses of critical resources and provide a framework to get back to business as usual.
An example of a winter weather emergency and continuity plan includes the following (10,11):
– Risk assessment specific to the organization (e.g., transport to work, supply network, potential damages to structures)
– Define the responsibilities of all internal and external parties of the company (property manager, person responsible for keeping equipment safe, for communicating weather updates and advisories, etc.)
– Managing stock efficiently, and ensuring redundancy of essential suppliers
– Establish a dedicated communication system, such as an emergency messaging tool to inform all internal and external parties
– Establish an emergency protocol (e.g., deciding when the company should close, if and how employees should continue to work, preparing a checklist for each necessary step, emergency training of employees, adapting stocks)
– Conduct regular inspections and maintenances to protect/prepare facilities against extreme winter weather
– Run tests to revise and refine the winter weather emergency plan
Experience shows that organizations that have undertaken a long-term resilience planning approach to ensure the security of the company and its stakeholders, and the continuity of their business are the most resilient to extreme situations.
Experience shows that organizations that have undertaken a long-term resilience planning approach to ensure the security of the company and its stakeholders, and the continuity of their business are the most resilient to extreme situations.
