Thundersnow hits Toronto and Michigan: Why is it happening?

A rare combination of a snowstorm and lightning were sighted after a monstrous winter storm wreaked havoc across the US

A winter snowstorm that left at least 12 dead across the United States bore down on the Northeast on Friday, dumping up to 30cms of snow and causing severe coastal flooding.

The powerful system brought tornadoes, torrential rain and tree-toppling wind gusts to the South and Midwest on Friday, leaving more than one million people without power across several states.

Residents of Michigan and Toronto reported seeing thundersnow on Friday night, a rare weather phenomenon when lightning and thunder accompany snowfall. 

According to the National Severe Storms Laboratory, thunderstorms occur when there is abundant moisture above a warm front, an unusual combination in winter. 

The storm cut a path across a vast swath of the United States on Friday.

In Kentucky, four people were confirmed to have died, Governor Andy Beshear said in a tweet on Saturday after declaring a state of emergency.

Two died in Tennessee after being struck by falling trees, officials told CNN. Deaths were also reported in Alabama, Mississippi, California and Arkansas.

The National Weather Service’s Louisville office described the storm as “powerful and historic”, with wind gusts reaching 128 kph on Friday.

THUNDERSNOW!! SE Michigan. pic.twitter.com/leAW9OHJS2

— Chase S (@Chase_S20) March 3, 2023

Winds ripped the roof of a house in Little Elm, north of Dallas, and overturned four 18-wheelers, according to the Associated Press.

The National Weather Service warned of heavy snowfall across upstate New York and New England on Saturday afternoon.

Coastal areas of Rhode Island and Massachusetts were under a flood warning on Saturday, with up to 45cms of snow expected.

Up to 1.5m of snow was also forecast in California’s Sierra Nevada mountain range, an area that had already been buffeted by back-to-back winter storms in recent weeks.

“An additional several feet of snow will be possible in these areas, with the heaviest of these totals likely in the northern Sierra Range, ” the weather service said. “On Sunday, precipitation will spread inland, with heavy snow possible in the higher terrains of the Intermountain West.”

Ross Weaver plows out a section of road in front of his home in Farmington Hills, Michigan, on Saturday after a winter storm left several inches of snow across the Metro Detroit area. (AP)

The storm took aim at Michigan on Friday, blanketing streets under 8cms of snow and bringing blizzard-like conditions.

The Detroit Metropolitan Airport was forced to close for several hours on Friday night due to the rapidly deteriorating conditions.

According to poweroutage.us, more than one million people across Kentucky, Michigan, Tennessee, Ohio and West Virginia were without power on Saturday morning.

The Weather Network forecaster Mark Robinson toldThe Toronto Star that thunderstorms were “incredibly rare”.