A powerful storm brewing off the coast of the US northwest is forecast to deliver high winds, heavy rain, flooding, and significant snowfall, impacting over seven million residents in states along the Pacific Ocean.

The storm began affecting the region on Tuesday and is expected to intensify through the week, according to the National Oceanic and Atmospheric Administration (NOAA).

In addition to severe weather, the storm may cause flash flooding, rock slides, debris flows, and hazardous mountain conditions with heavy snow and blizzard-like visibility at higher elevations.

What Is a ‘Bomb Cyclone’?

A “bomb cyclone” occurs when a weather system rapidly intensifies, with its central air pressure dropping by at least 24 millibars within 24 hours. This rapid intensification gives the storm explosive power, bringing a range of severe weather conditions, from blizzards to heavy precipitation.

NOAA meteorologists attribute this storm’s development to a sharp drop in air pressure off the coast, which has significantly intensified the system.

When and Where Will It Hit?

The northwest is already feeling the storm’s initial impacts, with strong wind gusts recorded in the Seattle area. NOAA’s Weather Prediction Center warns that the storm will bring:

• Heavy Snow: Mountain ranges in the Pacific Northwest could see snow accumulation rates of 2-3 inches (5-8cm) per hour. Some areas may accumulate 10-20 inches (25-50cm) of snow, with winds reaching up to 65 mph (29 mps), creating dangerous whiteout conditions.
• High Winds: Coastal areas could experience power outages, downed trees, and high surf due to strong gusts.
• Intense Rainfall: Northern California and southwest Oregon are forecast to see the heaviest rain, increasing the risk of mudslides and flash flooding.

The US Weather Service has issued winter weather alerts and a winter storm warning through Wednesday for multiple areas along the Pacific coast. A “high risk excessive rainfall outlook” is in effect for northwest California.

“Numerous flash floods, hazardous travel, power outages, and tree damage can be expected as the storm reaches max intensity,” NOAA said in a statement.

A Dangerous Combination

This bomb cyclone is further intensified by an atmospheric river, a narrow band of concentrated moisture traveling from tropical regions. When these two phenomena combine, they can produce a major weather event.

BBC Weather forecaster Helen Rossington noted that the storm will initially deliver strong winds, rain, and snow to the northwest coast before unleashing a prolonged period of heavy precipitation, mountain snow, and increased flood risk.

Seasonal Yet Severe

While such atmospheric river events are typical for this time of year, their combination with a bomb cyclone amplifies the storm’s severity. Similar systems have affected North America in recent weeks, underscoring the volatility of late autumn weather along the Pacific coast.

Residents are urged to prepare for hazardous conditions as the storm continues to gain strength.