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What makes a storm a nor'easter?

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  • HLN Meteorologist Bob Van Dillen discusses the science behind the storm
What is a nor'easter?

Another week, another type of storm is hammering the Northeast. This one isn’t a hurricane like Sandy, though, but a fall/winter storm called a nor’easter. So what's the difference?

Here are the basics:

A hurricane is a storm that forms in the tropics, has a warm center along with an eye in the middle. A nor'easter is a cold-core system and doesn’t have an eye, but its winds can gust to hurricane strength. 

A nor’easter has its roots in Canada and the northern United States. Cold energy rolls down from Canada and hits the East Coast of the U.S. (see the map of a typical storm track above). The energy gets transferred off the coast and into the ocean where it explodes as it hits the warm Mid-Atlantic waters, especially the gulf stream that flows up the East Coast. The warmer air over the ocean begins to rapidly rise through the cold air surging in from the mainland, and the pressure starts to fall. That's the classic ‘bombing’ of the storm as it heads north, propelled by the jet stream.  

If the storm hugs the coast it will be a snow event for the Appalachians but mostly rain for the big cites of D.C., Philly, New York and Boston. If the track takes it out to sea a bit more, the cold air will be in place along the coast and those cites will get rocked by a big, heavy, wet snow. This is what happened last night!

The Northeast has had one of each in the past two weeks -- a one-two punch like I have never seen before! It’s been awful to watch.

WATCH: Bob Van Dillen's Sandy video-diary - it's been crushing

HOW TO HELP: Severe weather victims in the Northeast

Morning Express with Robin Meade airs Monday through Friday at 6 a.m. ET on HLN.  Like the show on Facebook, follow Meteorologist Bob Van Dillen on Twitter: @BobVanDillen.

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