A “bomb cyclone” threatens California. Here’s what that means
On Wednesday and Thursday, areas of northern and southern California are poised for excessive rainfall, widespread flooding, landslides, heavy snowfall and extremely high winds, according to the National Weather Service. And there are two culprits behind the predicted devastation: a major storm known as a “bomb cyclone” and an aerial phenomenon called an “atmospheric river.”
“Now is the time to complete storm preparations,” an NWS representative said Wednesday, according to an online transcript of the organization’s San Francisco Bay Area forecast discussion. “But that window is closing, as the winds will only continue to increase throughout the day.”
So what do “bomb cyclone” and “atmospheric river” mean? And why are they ominous enough to prompt organizations like the NWS to urge West Coast residents to prepare for a “brutal system” that could result in loss of life?
What is a Bomb Cyclone?
Simply put, a bomb cyclone is a large, intense storm associated with a sudden and significant drop in atmospheric pressure.
In general, cyclones, which are basically giant, rising columns of air, form when a low-pressure air mass meets a high-pressure air mass. But bomb cyclones occur when the pressure drops suddenly and sharply in the low pressure mass section. This makes the pressure difference between the two masses much more pronounced, which intensifies the winds correlated to the storm.
You can imagine the bomb cyclone column rising very quickly all of a sudden, lowering the air pressure in the center much too quickly and creating a sort of vacuum effect, producing ultra-strong winds in the process.
Meanwhile, Earth’s rotation is pushing these high-intensity winds around the world, like those set to land in California on Wednesday and Thursday.
Specifically, these powerful gusts are likely to pound the coast at speeds reaching between 60 and 65 miles per hour (97 and 105 kilometers per hour). On higher ground, according to the NWS, their speeds can even reach 80 miles per hour.
“These strong, gusty winds today are going to knock down trees and potentially create power outages,” the NWS representative said during Wednesday’s chat, noting that the storm has already started to close in but will soon slacken. ‘intensify.
To make matters worse, this bomb cyclone is accompanied by what is called an atmospheric river.
What is an atmospheric river?
Atmospheric rivers are essentially narrow currents, or rivers, in the air that carry a lot of water vapor around the world. They transport most of this water vapor outside the tropics and then release it as rain or snow.
Smaller, weaker atmospheric rivers are generally not a major threat – most of these mini-rivers are actually considered good for replenishing our water supply – but more extreme versions of these events have the potential to create flooding and causing mudslides.
And the one meteorologists are currently warning about is seen as a big deal. It is even expected to be stronger than the last atmospheric river to hit California over the New Year’s weekend, leading to major flooding, dozens of cars stranded on highways and thousands homes without electricity.
So, coupled with the Bomb Cyclone directed toward the West Coast, this particular atmospheric river could wreak quite a bit of damage on the California coast, from places near Sacramento all the way to Los Angeles. The bomb cyclone will more or less “drag” the atmospheric river.
“Rain is likely to persist for much of the day across North Bay where the atmospheric river will be placed ahead of the main cold front,” the NWS said. “Don’t let your guard down if things seem calmer than you expected this morning.”
It won’t be a “one and done” storm
The NWS also issued a warning that precipitation and thunderstorms will increase in both coverage and intensity between the afternoon and evening, as well as expect increases in streams, streams, rivers and flooding in urban areas.
As for the timing, the organization estimates that the high winds from the storm will diminish early Thursday morning, but rain showers and thunderstorms will continue for much of the day. Ultimately, the agency says, there will likely be around 1 to 3 inches (2.5 to 7.6 centimeters) of flooding in urban areas, 3 to 4 inches (7.6 to 10.2 centimeters ) in the North Bay Valleys, and by Friday morning, 3-6 inches (7.6-15.2 centimeters) in the Coast Ranges and over 8 inches (20.3 centimeters) in the wettest areas like the Santa Cruz Mountains, just over 70 miles (112 kilometers) south of San Francisco.
The risk of shallow landslides, landslides and mudslides in hilly or mountainous areas will persist. On Friday, there could be a break in rainfall, but an extension of the storm is expected to continue intermittently through Tuesday – and could possibly extend until around January 16.
“The message to convey is resilience, as this is not a ‘one-and-done’ storm,” the NWS said. “Of course, the timing and details of subsequent systems will be subject to change. Be sure to stay tuned for the latest information in the coming days,” the discussion concluded.
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