A monster winter storm slammed central United States on Wednesday, March 13, becoming a "bomb cyclone" and bringing heavy rains, strong winds, and severe blizzard conditions in the region. Heavy snow reportedly lashed northern Colorado, including Denver, western Nebraska, central South Dakota, southeastern North Dakota, and eastern Wyoming.

The Colorado governor declared a state of emergency and activated the National Guard as millions of residents are expected to be affected by the storm. In a tweet, Jared Polis added that the National Guard would carry out "search, rescue & safety ops," and the emergency department would work with local counties.

What is a bomb cyclone?

A bomb cyclone, also called Bombogenesis, is a storm, which can be tropical or non-tropical in nature, and strengthens at a fast face, according to Accuweather. It comes from the words bomb and cyclogenesis and means the strengthening of a massive cyclone.

Common over the east coast, the storm is a result of "cold air along the land, and warm air over the water."

The National Oceanic and Atmospheric Administration explains that a Bombogenesis occurs when "a midlatitude cyclone rapidly intensifies, dropping at least 24 millibars over 24 hours."

"In this case, bomb refers to explosive development. Altogether the term means explosive storm strengthening," AccuWeather senior meteorologist Alex Sosnowski said in a blog post.

In tune, the National Weather Service (NWS) recorded about 350 wind gusts of over 80 kilometre per hour or more in a span of 24 hours and also received about 92 reports of damage. "There have been gusts to near 100 mph with the snow in Colorado Springs, Colo.," AccuWeather's Dave Samuhel said.

Over 1,100 motorists were said to have been stuck in Colorado and rescue personnel are carrying out efforts to help them. A Colorado State Patrol officer, Cpl. Daniel Groves was also killed on Wednesday after he was struck by a vehicle while helping another that had slid off the road. "He was transported to Platte Valley Medical Center but declared deceased a short while after arrival," the patrol said in a statement.

"The case is under investigation by the Colorado State Patrol and all parties are considered innocent until proven otherwise. Charges have not been filed."

Ryan Parsell, a spokesman for El Paso County, also said that the massive storm has affected many people and rescue operations are in full swing. "We are in full saving lives mode. This isn't your average Colorado storm," CNN quoted him as saying.

Several roads and highways remain closed in the region and the Denver International Airport's runways were also completely shut down, affecting about 1,400 flights. DIA spokesperson Emily Williams said that the runways were covered with snow and it was even dangerous for plow drivers to work.

"Conditions are very dicey right now and because of all the accidents the plows can't clear the roads," Williams said, according to the Denver Post. "If people can avoid coming to the airport that will be the best for everyone."

Bomb Cyclone in US
Bomb Cyclone in USMaddie Meyer/Getty Images