by Peter Mertz
DENVER, the United States, March 13 (Xinhua) -- A sudden drop in barometric pressure unleased a rare "Bomb Cyclone" over state of Colorado Wednesday, crippling the region with heavy snows and high winds.
As many as 74 million Americans will be affected by the storm which hit southern Colorado with Category 2 hurricane conditions Wednesday morning and 100-mile-per-hour winds, according to the National Weather Service (NWS).
"This is a serious blizzard! DO NOT EVEN ATTEMPT TO DRIVE IN THIS STORM!" NSW Boulder posted on Twitter Wednesday afternoon.
Thousands of cars were abandoned along Colorado roadways as "the bomb cyclone wreaked havoc, triggering innumerable crashes, and leaving people stranded in cars," the Denver Post reported.
"This is a very epic cyclone," said Greg Carbin, chief of forecast operations for the National Oceanic and Atmospheric Administration's Weather Prediction Center. "We're looking at something that will go down in the history books," Carbin said.
It could develop into the worst storm of its type in 35 or 40 years, he added.
Colorado's capital Denver was the first major metropolitan area hit by the storm, where newly elected Governor Jared Polis issued a state of emergency and called in the National Guard to help.
"I couldn't see 10 feet (3 meters) away," Denver builder Jason Griggs said, who was driving home to Denver from Boulder when the storm suddenly struck.
"The wind was so powerful it blew cars off the road, and the snow was so heavy it covered you in seconds," he told Xinhua.
More than 55 million people are "threatened" by high winds, 10 million by winter storms, and more than 17 million by floods, with "severe storms capable of producing damaging winds, hail, and tornadoes -- forecast from the southern Plains and into the Mississippi River Valley," the NWS said on its website.
"A bomb cyclone happens when there's a rapid pressure drop, with a decrease of at least 24 millibars (which measures atmospheric pressure) over 24 hours known as "bombogenesis," the Weather Channel said.
"This storm has dropped 33 millibars since Tuesday morning and continues to strengthen," it added.