
A historic blizzard that could break records for April has hit the Great Plains and Upper Midwest.

Parts of six states were under blizzard warnings on Wednesday, in an area that included Denver; Cheyenne, Wyoming; Scottsbluff, Nebraska; and Pierre, South Dakota.

Early on Wednesday morning, thundersnow was reported in Pierre and surrounding parts of South Dakota, as well as southern Minnesota.

Snow accumulation had already reached 18 inches in parts of South Dakota by noon on Wednesday, with multiple feet possible by week's end.

It came as a shocking reversal after warm spring weather in the region - Denver, for instance, saw a high of 78 degrees on Tuesday.

Meteorologists said on Wednesday afternoon that the storm system had met the definition of a 'bomb cyclone', in which atmospheric pressure drops 24 millibars in 24 hours.

Winter Storm Wesley will continue to hammer the Plains and upper Midwest with heavy snow and high winds on Thursday, including blizzard conditions, creating dangerous travel and possibly triggering scattered power outages

Parts of six states were under blizzard warnings on Wednesday, in an area that included Denver; Cheyenne, Wyoming; Scottsbluff, Nebraska; and Pierre, South Dakota

Alan Brown of Colorado Springs, Colo., attempts to clear ice from his truck's license plate as he prepares to continue the trek to Billings, Mont., while passing through Love's Travel Stop during a blizzard warning hitting southeast Wyoming Wednesday, April 10, 2019, in Cheyenne

A truck travels east on Interstate 80 during a blizzard warning hitting southeast Wyoming and the Colorado Front Range on Wednesday in Cheyenne

Snow blocks a walking sign after initial snowfall and before a blizzard warning went into effect for southeast Wyoming on Wednesday in Cheyenne. The storm was bringing snow to an area stretching from Colorado and into Montana

Joshua Carpenter, with Meyer Outdoor Services, sprinkles salt on Peace Plaza sidewalk as snow falls Wednesday in Rochester, Minnesota

Pedestrians opt for the skyway as snow falls Wednesday in downtown Rochester, Minnesota

A tractor-trailer was disabled in the bad road conditions near Rapid City, South Dakota on Wednesday

Other vehicles ran off the road in the Rapid City area as police urged everyone to avoid travel for any reason

Blizzard conditions are seen in Perkins County, South Dakota on Wednesday morning as snow accumulates

Some areas are predicted to see as much as two feet of snow by Friday, as seen in the forecast map above

Last month, a deadly bomb cyclone hit Colorado and Nebraska, killing several people.

Forecast models predict that the new storm, which is already disrupting travel with life-threatening blizzard conditions, will increase in strength between Wednesday and Friday, and could produce a blizzard of record proportions.

High spring temperatures will give way to heavy snow, gale-force winds and life-threatening conditions across a swathe of the central United States running from the Rockies to the Great Lakes, according to the National Weather Service.

'This is potentially a life-threatening storm,' Patrick Burke, a meteorologist with the NWS's Weather Prediction Center in Maryland, said Wednesday.

More than 500 flights were canceled at Denver International Airport on Wednesday, about a quarter of its total schedule, according to FlightAware.com, an airline tracking website.

Airport officials said they had snow-removal crews in place.

Conditions were near-whiteout on Wednesday in South Dakota, where state troopers came across this crash

A view from Wednesday afternoon shows the treacherous conditions in northern South Dakota as snow accumulates

South Dakota's highway patrol warned of hazardous road conditions in the western part of the state (seen above). 'Please stay home if possible,' the agency warned

'Thunder-sleet' and snow was reported in Brookings, South Dakota (above) on Wednesday morning

Snow is seen early on Wednesday in Red Lodge, Montana, making roads hazardous and travel dangerous

The storm is expected to bring blinding, heavy wet snow across the region, likely downing trees and causing widespread power outages, widespread road closures and making driving treacherous, Burke said.

'It's slow moving. It won't push farther east until Friday,' he said.

Some areas of western Minnesota and southeast South Dakota were expected to get up to 30 inches of wet, heavy snow, the NWS said.

South Dakota Governor Kristi Noem has closed state government offices in 52 counties. Numerous schools around the state have closed.

Minnesota Governor Tim Walz says 'the National Guard stands ready' to rescue any stranded motorists.

Parts of six states were put under blizzard warnings on Wednesday morning, as seen in the map above

Wednesday's forecast shows bands of snow and rain covering the Plains and upper Midwest

The storm is not predicted to move much by Thursday, potentially inundating certain areas with feet of snow

Two factors may limit the flooding effect, forecasters said. Thawed ground will be able to absorb more precipitation than last month's frozen ground and a fall of heavy snow rather than rain will slow the runoff process.

The coming storm was expected to exacerbate flooding along the Missouri River in areas where dozens of levees were breached in March, exposing communities to future surges.

The river was not expected to crest in areas of Nebraska, Iowa and Missouri until between three to five days after the storm.

The storm is expected to weaken and push off into the Great Lakes area and northern Michigan on Friday, bringing more rain and snow, the weather service said.