An extreme cold warning was issued in the Berkshires due to temperatures that could cause frostbite on exposed skin in as little as 30 minutes. Parts of Western and Central Massachusetts could also experience temperatures that could cause frostbite in 30 minutes. But a majority of the state, including Springfield, Worcester and Boston, is under a cold weather advisory. “The dangerously cold wind chills as low as 20 below zero could result in hypothermia or frostbite if precautions are not taken,” the National Weather Service warned. The following school districts have announced delays — and at least one closing — Friday, Jan. 30.