Nightly News   |  January 31, 2012

January or June-uary?

A new jet stream is causing high temperatures across the U.S. making for a nontraditional winter. NBC’s Anne Thompson reports.

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This content comes from Closed Captioning that was broadcast along with this program.

>>> what a difference a year makes. if you live anywhere from boston to chicago or points in between and you walked out the door this mourning and turned right around to take out a few layers, who would blame you. some people did put their coats away here in new york today. it was so warm today across much of the country. as you know, they're kuling it june-uary. it's got a lot of people wondering whatever happened to winter? again, realizing we're tempting fate, we get the story tonight from our chief meteorological correspondent, anne thompson .

>> in new york city central park today, it might as well be spring.

>> i heard it was so warm out, i had to come out and take a walk.

>> reporter: this most unusual january ending on a remarkably mild note across the country. today they hit the links in north platt, nebraska. took to skateboards in northern virginia and sported shorts in st. louis.

>> i would much rather be walking on the hills than sledding down it.

>> reporter: this is a january for the history books. 2,890 daily high temperature records broken or tied. more than four times the number of highs reached or exceeded last year. while today is certainly worthy of a walk in the park, it's also a good time to take a stroll down memory lane . a year ago, the nation braced for 2011 first billion dollar-plus weather event, the groundhog day snowstorm.

>> how long have you been in here?

>> 7 1/2 hours.

>> reporter: today it was a perfect day to get that same car washed.

>> i have no jacket, no glove, no scraper in my hand and i can see my car.

>> reporter: the difference is the jet stream . last year, it followed a typical la nina pattern, bringing warmer and drier temperatures to the south and colder and wetter conditions to the north.

>> what happened this year is this pattern shifted to the north and now almost all of the country is covered by this drier la nina pattern.

>> reporter: add warming because of climate change and it stacks the deck against a traditional winter.

>> we just shift the odds towards a better chance of record warmth and a reduced chance of record cold.

>> reporter: leaving much of america with a very early case of spring fever . anne thompson , nbc news, new york.