Dangerously cold air sent temperatures plummeting Thursday around the U.S., resulting in school cancellations, a fatal car pileup and worries about the homeless.

School districts from the South to the Northeast and Midwest were delaying the start of classes or canceling school altogether.

Many cities experiencing cold weather opened warming stations for residents lacking heat. But extra care was being taken to protect the homeless.

In New Jersey, some officials empowered law enforcement to move homeless people off the streets and into shelters.

Blankets were given out at some of the 15 small tent cities around Huntsville, Alabama. Workers from a nonprofit organization there encouraged residents of the encampments to come inside. Some people planned to stay at a church that was opening as a shelter.

Authorities said the severe weather and blowing snow are factors in the deaths of two northern Michigan men — an 85-year-old who was struck by a car while crossing a road to get his mail and a 64-year-old who was hit by a car while clearing snow.

In western Pennsylvania, an 18-vehicle pileup that happened in whiteout conditions on an interstate has left two people dead and nearly two dozen injured.

At least one of the trucks was carrying hazardous material, but no leaks were found.

None of the injuries was thought to be life-threatening, but three of the approximately 20 people taken to a hospital apparently had serious injuries. The others were treated for everything from bumps to broken bones.

In Ohio, a space heater being used to thaw frozen pipes was the likely cause of a barn fire that killed more than a dozen horses, fire officials said. Firefighters were hindered by temperatures hovering around 3 degrees Fahrenheit (-16 Celsius).

In western New York, where the Buffalo area got slammed with more than 7 feet (2.13 meters) of snow in an historic November storm, 12 inches (30.5 centimeters) fell on Tuesday. Thursday night and Friday could bring up to 10 inches (25.4 centimeters) more, weather forecasters say.

Meanwhile in the Southwest, Phoenix posted a record high temperature of 80 degrees Fahrenheit (26.6 Celsius) on Wednesday. That broke the old record of 79 Fahrenheit (26.1 Celsius) set in 1948.

The National Weather Service recently announced that 2014 was the warmest year ever recorded in Arizona.