Today’s Image of the Day from NASA Earth Observatory features a strong extratropical cyclone, which struck the Pacific Northwest on November 19, 2024.

“The storm knocked over trees and left nearly 600,000 people without power in Washington state on November 20, according to news reports,” noted NASA. “This image shows the storm system at 1:50 p.m. Pacific Time on November 19.” 

According to NASA, mature extratropical cyclones like this often feature comma-shaped cloud patterns that are the product of ‘conveyor belt’ circulation. “Heavy precipitation is often present near the low-pressure head of the comma.”

Impacts of the extratropical cyclone 

The “bomb cyclone” brought severe weather, including strong winds exceeding 70 mph, heavy rainfall, and snow in higher elevations. These conditions led to significant disruptions, including downed trees and hazardous travel conditions.

In urban and rural areas, damage to infrastructure and properties was substantial, with emergency responders and utility crews working around the clock to restore services. 

Additionally, mountain passes faced dangerous blizzard conditions, with up to 20 inches of snow accumulating in some areas, severely affecting travel.

Rapid pace of acceleration

Chris Dolce is a meteorologist at The Weather Channel. He noted that on the evening of November 19, the storm’s central pressure dropped to levels on par with a storm in October 2021, which saw the lowest pressure in about 50 years of records for that region.

“The pace of the storm’s intensification was more than double the criteria for bombogenesis – a popular term that describes a midlatitude cyclone that rapidly intensifies into a ‘bomb cyclone,’” said NASA.

The rapidly dropping atmospheric pressure at the center of the storm caused winds to intensify quickly. According to the National Weather Service in Seattle, wind gusts reached up to 77 miles per hour in the mountains southeast of the city.

“The cyclone kicked off a long-duration atmospheric river that forecasters expect will park over Northern California and southern Oregon through November 22. The National Weather Service estimates that these areas could see rainfall totals of 12 to 16 inches over the duration of the storm,” noted NASA.

What is an extratropical cyclone?

An extratropical cyclone is a large-scale weather system that forms outside the tropics, typically between 30° and 60° latitude, and is associated with areas of low pressure. 

Energy source

These cyclones obtain their energy from the contrast in temperature between air masses, such as cold polar air and warm subtropical air. This contrast creates instability and drives atmospheric circulation.

Development of extratropical cyclones 

Extratropical cyclones usually have well-defined warm and cold fronts. They often develop along the polar front, where cold and warm air masses meet.

A common area for their development is the mid-latitudes, particularly in regions like the North Atlantic and North Pacific.

Weather conditions

Extratropical cyclones can bring a variety of weather conditions, including heavy rain, snow, strong winds, and severe storms. They are responsible for much of the day-to-day weather in mid-latitude regions.

Tropical vs. extratropical cyclones 

While tropical cyclones derive energy from warm ocean waters and have a warm core, extratropical cyclones gain energy from temperature contrasts and have a cold core.

Tropical cyclones typically lack fronts, whereas extratropical cyclones are defined by them.

These systems are essential in distributing heat and energy across the planet, playing a critical role in the Earth’s climate system.

Caught off guard by the weather

The bomb cyclone in the Pacific Northwest highlights the importance of preparedness, as residents were urged to secure loose outdoor items, stock emergency supplies, and avoid unnecessary travel.

The fire department in Bellevue, east of Seattle, posted a Severe Weather Safety alert on Facebook: “It’s severe out there. Trees are coming down all over the city, with multiple falling onto homes. If you are able, head to the lowest floor you can and stay away from windows. Do not go outside if you can avoid it.”

The image was captured by the VIIRS (Visible Infrared Imaging Radiometer Suite) on NOAA’s JPSS-1 (Joint Polar Satellite System-1).

Image Credit: NASA Earth Observatory

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