CNN News:极地漩涡来袭 美国多地迎来最冷12月

Our first story this December 14th — baby, it's cold outside. Two-thirds of the United States, the eastern two-thirds, are seeing record-breaking winter temperatures. Some places have recorded their coldest December day ever. What means, this could be one of America's coldest winters in years.
From North Dakota to Massachusetts, wind chill temperatures, what the cold feels like when the wind hits you, were expected to be between negative 10 and negative 35 degrees Fahrenheit. That can cause frost bite within minutes on uncovered skin.
This latest Arctic blast follows a winter storm that struck last week, forcing thousands of airline flight cancellations in the Midwest and it was still coating New England with snow last night. And as this week goes on, U.S. temperatures are expected to get lower. How is this happening?
From the Gulf of Alaska in the Northern Pacific, a strong cold front blew southeast into the country and started frosting its way across America.
When a storm pattern like this hit the U.S. in 2014, meteorologists and the media were using the term "Polar Vortex". What exactly is that?

SUBTITLE: What is a Polar Vortex?
JENNIFER GRAY, AMS METEOROLOGIST: Polar Vortex was one of the most trending terms. We've heard it all the time. And, in fact, it's not something that's going to come and get you. It's not something you can be inside. It's not an alien. It's not a monster. It's not something that's going to invade the U.S.
In fact, the only way to be inside the Polar Vortex is to be in an airplane. It lives in the upper levels of the atmosphere. It's a low pressure system that's basically locked them to the North Pole.
So, it's not a hurricane. It's not a tornado. It's just an air mass that's locked right around the North Pole and it stays there all the time.
The frequency of the winter outbreak, this cold outbreak, is dependent upon the weather patterns across the U.S. It depends on when we have these large dips in the jet stream, the placement of high pressure, low pressure. So, it all depends on Mother Nature.
Extreme temperatures can be very dangerous. It all depends on the temperature, though, the bottom line. A lot of areas can have, if it's windy outside, you have a really low wind chill.
If you find yourself in the midst of one of these winter outbreaks, just remember, just try to stay warm. Put in as many layers as you can, bundle up, have a good jacket and try not to stay outside for a very long periods of time.