Il Nuovo Postiglione - Dozens rescued by helicopter in Yellowstone floods

Over three days Montana National Guard units scrambled to reach 87 people cut off by raging rivers that have swept through the park and its surroundings following torrential rain and rapid snowmelt.

"At the request of local officials, the Montana National Guard continues to assist with search and rescue operations due to significant flooding in South Central Montana," the National Guard said in a release Wednesday.

They have flown more than 41 hours of search and rescue operations, and also staffed road checkpoints to help with travelers' safety, the release said.

Thousands of visitors have been forced to leave Yellowstone, the oldest national park in the United States, where roads and bridges have been swept away by raging rivers.

Park managers said this week they expect sections of the park -- which chiefly lies in Wyoming, but also extends into Montana and Idaho -- will remain closed for the rest of the year because of the extensive damage caused by flooding.

Images released by the National Park Service showed large sections of paved road had been swept away by raging rivers.

Aerial reconnaissance revealed "major damage to multiple sections of road" in the northern part of the park, the agency said.

Several communities on the north side of the park in Montana also experienced significant flooding, with bridges and roads washed out in Park County.

Montana Governor Greg Gianforte declared a statewide disaster on Tuesday "to help impacted communities get back on their feet as soon as possible," he said on Twitter.

A huge dome of high pressure is sitting over the United States, sending temperatures soaring for tens of millions of people.

Meteorologists say the edge of that dome, where colder air meets warm air, is experiencing wild weather, including heavy rainfall.

Higher-than-usual temperatures have also caused snowpack on the high mountains to melt, adding to the influx of water into rivers.

L.Gallo--INP