A "bomb cyclone" (also known as Bombogenesis) happens when a cyclone develops so fast that it drops the atmospheric pressure by at least 24 millibars, according to NOAA.
The storm could rival one that hit the region in 1979 in terms of the extent of heavy snowfall, according to meteorologist Richard Emanuel with the National Weather Service in Cheyenne, where wind was gusting to 60 miles per hour (96 kph) with heavy snow.
'We expect a major blizzard to unfold with winds likely to approach hurricane force, heavy snow and massive drifts, ' according to AccuWeather meteorologist Alex Sosnowski. Per CNN, "more than [45 million] people are under a high wind threat; more than 10 million are under winter storm threats; and more than 15 million are under a flood threat".
More than 1,900 United States flights had been canceled by Wednesday afternoon, according to FlightAware. For the Dakotas, Nebraska, Montana, Wyoming, and Colorado, a blizzard warning was issued by the National Weather Service.
In Colorado, more than 133,000 people were affected by power outages, officials said.
The Lower Mississippi Valley and southern Plains will experience thunderstorms with heavy rain and flooding.
2 attackers kill 6, themselves at Brazil school
Doria said the school had been evacuated and police were inspecting what appeared to be possible explosives left by the shooters. The last one occurred in 2011, when the former student of a school returned and shot 12 children fatally, Fox News reports .
'We are advising to stay off the roads through the afternoon and evening, ' Treste Huse, a National Weather Service meteorologist in Denver, said on Tuesday afternoon.
In the Northern Hemisphere, areas of low pressure are called cyclones, and rapidly developing storms are often called bombs or weather bombs. The majority of those cancellations were flights destined for or originating at Denver International Airport (DIA), where a blizzard warning is in effect.
In the Denver area, blowing snow could cause unsafe blizzard conditions.
A 250-mile (402-kilometer) stretch of Interstate 80 from Cheyenne to Rock Springs in southern Wyoming was closed, along with a 300-mile (483-kilometer) section of Interstate 25 from Buffalo, Wyoming, to the Colorado border.
Rivers in Wisconsin are expected to reach flood stage over the next few days as thunderstorms and showers melt away snow that has accumulated this winter.
Thunderstorms across portions of the southern Plains will make way on Wednesday for sustained winds of 35 to 45 miles per hour, akin to the strength of a low-end tropical storm.