Devastating ‘Cyclonic Bomb’ Strikes Northwest United States and Canada

Extreme weather events are increasing and intensifying under the impact of climate change, redefining the limits of what infrastructure and populations can endure. Among them, rare but devastating cyclone bombs pose considerable challenges in terms of forecasting, impact management and resilience. This week, one of these storms violently hit the west coast of North America, combining destructive winds, torrential rain and exceptional snowfall to create a veritable “cyclonic bomb”.

Leading to massive power outages, human losses and major flooding risks, this weather event illustrates the growing vulnerabilities to extreme conditions. It also highlights the need to analyze these phenomena to anticipate their effects on communities and better understand the interactions between climate and extreme weather events.

But what is a “climate bomb”?

A “bomb cyclone” is an atmospheric depression that undergoes rapid intensification. It is scientifically defined by a drop in pressure of at least 24 hectopascals in 24 hours. A phenomenon known as “bombogenesis”. The cause? Complex interactions between cold and warm air masses, often in the presence of a powerful jet stream.

The drop in pressure causes rapid intensification of winds and precipitation. Which makes these storms particularly violent weather events. In this specific case, the pressure drop far exceeded the usual thresholds. It reached levels rarely observed in this region, according to the National Weather Service. These events, although rare, typically occur once every ten years in the Pacific Northwest. But their increasing intensity raises concerns about their link with climate change.

The effects of a cyclonic bomb are amplified when it interacts with other atmospheric phenomena, such as an atmospheric river. The latter refers to a dense flow of water vapor transported from tropical areas to higher latitudes. It creates a massive supply of humidity. When such a river encounters the dynamic conditions of a cyclonic bomb, the intensity of precipitation increases drastically. It causes torrential rains. In mountainous areas, this moisture transforms into heavy snowfall, sometimes measured in meters. In the case of this storm, winds exceeding 160 km/h were recorded in British Columbia. Waves up to 10 meters were observed off the Pacific Northwest. The intensity and combination of these elements demonstrate the extreme power of these meteorological phenomena, exacerbated by unusual climatic configurations.

Tragic human and material consequences

The human and material consequences of this cyclonic bomb have reached a worrying scale. Particularly in Washington State and British Columbia. More than 700,000 homes and businesses were without power in Washington state, complicating relief efforts. The massive fall of trees blocked several roads. Local authorities, overwhelmed by the scale of the damage, described a chaotic situation, marked by impassable roads and entire isolated neighborhoods.

© REUTERS

The human toll is just as dramatic. In Seattle, a woman lost her life when a tree collapsed on her house while she was in the shower, an incident that illustrates the brutality of the storm. Another victim was reported at a homeless encampment in Lynnwood. These tragic events were exacerbated by damaged infrastructure, notably the railway network. In Stanwood, an Amtrak train struck a tree that had fallen on the tracks, stranding dozens of passengers for several hours. The storm also forced the closure of many schools. These disruptions, described by Mary Lou Pauly, Mayor of Issaquah, as being among “the worst storms in recent years”, underline the urgency of reinforced preparation for such phenomena.

Increased risk of secondary disasters

The massive rainfall associated with this bomb cyclone poses a critical threat. This is because of the flash floods and landslides they could trigger. In some areas of Northern California, up to 400 mm of rain is forecast in just 48 hours. This is equivalent to several weeks, or even months, of precipitation concentrated in a very short period of time. Such intensity of precipitation greatly exceeds the absorption capacity of the soil. The latter, already saturated by previous rains, significantly increase the risk of devastating floods.

THE Weather Prediction Center (WPC) has also classified these risks at level 4, the highest. This level is rarely reached, but responsible for the majority of damage and human losses linked to floods in the United States. These heavy rains, in conjunction with rugged topography, also promote landslides and debris flows. Another threat to infrastructure and homes located in sensitive areas.

In mountainous regions, conditions are even more complex due to the heavy snow deposited by the storm. Avalanches become an immediate threat. Especially in areas where fresh snow is unstable due to strong winds and rapid temperature fluctuations. Added to this is the melting of snow expected at the end of the week, caused by a rise in temperatures. This phenomenon, combined with persistent rain, worsens the floods. It increases the volumes of water flowing to downstream river basins. Local authorities have issued warnings to limit travel in these high-risk areas.

A cyclone bomb as a warning about climate change

This event powerfully illustrates the growing influence of climate change on extreme weather phenomena. Recent studies show that global warming intensifies atmospheric rivers. Combined with explosively intense depressions like bomb cyclones, they produce devastating storms of a magnitude once rare. “ These events are not new, but their power and regularity are increasing, underscoring the climate emergency », alerts Stav Danaos, weather presenter of the BBC. Comprehensive measures to limit temperature increases and reduce greenhouse gas emissions must be adopted.

More resilient infrastructure and reimagined urban planning are becoming essential to address these conditions. At the time of COP 29, the question of investment in adaptation and prevention strategies is at the heart of the discussions. Calls to include specific financial commitments for the most vulnerable countries are increasing, emphasizing that a global and equitable response is essential to limit the human and environmental impacts of these crises.