A powerful storm is moving across the United States that has weather elements of both a winter and spring.

This storm originated out of the eastern Pacific and moved into the western US earlier this week. But it was not until Wednesday that the low began to deepen and intensify.

Storms at this time of year often have characteristics of both winter and spring weather because during this transition time temperature contrasts across the US tend to be extreme.

Already, the massive system has brought heavy snow to seven states across the West, Northern Plains and Midwest. In Montana, 58cm of snow has already fallen, while the states of South Dakota and Wyoming have picked up over 45cm. Hurricane-force winds of up to 107kph have been reported in Colorado.

Conditions associated with the storm are only getting worse. Six states are currently under blizzard warnings with an estimated 15 million people expected to be affected by the winter weather. Over 50cm of snow is forecast to fall in South Dakota and a widespread area of over 25cm from the Plains into the Midwest.

Winds of up to 80kph, combined with falling snow, will mean dangerous white-out conditions on the roads, as well as widespread power outages.

East of the storm, where temperatures are much warmer and there is an abundance of moisture from the Gulf of Mexico, thunderstorms are expected to develop on Thursday evening and into the overnight hours with the risk of damaging wind gusts and hail.

On Wednesday, there were over 4,500 airport delays and cancellations because of the weather conditions. Another day of travel disruptions is expected on Thursday with major airports such as Minneapolis and Chicago expected to be affected.

By Friday evening, the storm will weaken but continue to move into southeastern Canada. Snow will be a factor for the southern parts of the provinces, but accumulations are not forecast to be as high.