A storm the National Weather Service called a "once in a generation" blizzard is brewing in the northern part of the country. A blast of Arctic air advanced over much of the U.S. on Thursday, triggering dramatic temperature drops. More than half of U.S. states were forecast to see some areas with minimum wind chill temperatures in the negative double digits in coming days, and the coldest regions were bracing for wind chills below minus 50 degrees, according to the National Weather Service. There will be "dangerously cold conditions across most of the country this week," the weather service said. 📸 USA TODAY Network, @apnews #snow #winter #weather