A 'monster' coming this weekend: Bomb cyclone, atmospheric river to blast western U.S.
A series of strong storms will bring rain and snowflakes over the west over the next few days, including one on Sunday known as the "bomb cyclone" because of its severity.
Charged by a classic atmospheric river pattern, the storms could lead to flash floods and dangerous debris flows in much of the region that has already been devastated by forest fires, CNN said.
Despite the danger, rain and snow will be welcome in the drought-stricken areas of the west. According to Thursday's US Drought Monitor, almost 92% of the western US is in some drought. The rain will help stop smoldering forest fires and could ease water restrictions on farmers.
California has been particularly hard hit by the drought. It had some of the hottest, driest months on record last year. Some of California's major reservoirs are at or near historic lows in the rainy season.
"The pattern unfolding from this to next week may well be one of the largest rainy season storms for California, but there is still potential for a few larger winter storms," said AccuWeather forecaster Paul Pastelok.
Emily Heller, a meteorologist for the National Weather Service in Sacramento, said, "This is definitely going to be one of those landmark events."
The western United States will have a stormy, humid weekend, forecasters say.
What is a bomb cyclone?
Meteorologists define a bomb cyclone as a rapidly intensifying storm with a central pressure that drops 24 millibars or more in a 24 hour period, AccuWeather said. The process is known as bombogenesis.
A millibar is a measure of the pressure. The lower the pressure, the stronger the storm.
The cyclone will compete in some respects with the intensity of strong hurricanes from the Atlantic this season. For example, according to AccuWeather, the bomb cyclone could reach the intensity of Hurricane Larry, a long-lived and intense cyclone that swirled across the Atlantic in early September.
Meteorologist Ryan Maue tweeted that "this hurricane-force monster-bomb cyclone will challenge the historical low pressure observed off the US west coast this weekend."
What is an atmospheric flow?
According to a 2017 study, atmospheric rivers are responsible for up to 65% of extreme rain and snow events in the western United States.
"An atmospheric river labeled Category 4 or 5 can produce remarkable amounts of rainfall over three days or more, likely exceeding 10-15% of typical annual rainfall in some locations," said Marty Ralph, director of the Center for Western Weather and Water Extremes at UC San Diego, CNN said.
The atmospheric flow this weekend could be a rare Category 5 event, he said.
Visible through clouds, these steam bands stretch thousands of kilometers from the tropics to the western United States. They provide the fuel for the massive rain and snow storms and subsequent floods along the west coast.
While these events are beneficial to water supplies, they can cause devastating travel, trigger deadly mudslides, and cause catastrophic damage to life and property, the National Oceanic and Atmospheric Administration said.
A well-known nickname for an atmospheric river is the "Pineapple Express," which occurs when the source of moisture is near Hawaii.
According to NOAA's Earth System Research Laboratory, a single strong atmospheric river can carry up to 15 times as much water vapor as the average water flow at the mouth of the Mississippi.
Contribution: The Associated Press
This article originally appeared on USA TODAY: Bomb Cyclone, Atmospheric Flow to Blow Up the Western United States this weekend
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