Why so much early snow in the Northeast? - Tucson News Now

Why so much early snow in the Northeast?

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Source: AP/Jessica Hill Source: AP/Jessica Hill

TUCSON, AZ (KOLD) - The Northeast record breaking snowstorm was a combination of cool air clashing with tropical moisture. While the temperatures were chilly, the air was actually barely cold enough for snow.  That created a slushier, wetter snow that has a high water content. This makes the snow very heavy. As the snow piled on branches, still full with fall leaves in some spots, the weight was too much for the trees to bear. These branches broke, taking down power lines running below the branches, dropping on houses and cars, and blocking roads and rail lines. 

The Northeast is prepared for fall cold snaps and this one was not all that unusual.  According to the National Climate Data Center (NCDC), two record cold temperatures were recorded on Saturday, October 29th in the Northeast (New York and Pennsylvania).  On Sunday, only two more record cold temperatures were recorded (New York and Pennsylvania).  But on Saturday 69 record snowfall amounts were set with two others matched inch for inch.  On Sunday 127 snowfall records were exceeded or matched. 

Why so much snow?  Believe it or not, it has to do with the tropics.  The ocean surface temperatures are running warm for this time of year across much of the Atlantic Ocean, including in the Caribbean.  The means the tropics are still active, which is not unusual since Hurricane Season doesn't end until November 30th. 

Atlantic Basin Sea Surface Temperature Anomaly for October 29, 2011

And just how did all this tropical moisture get to the Northeast?  That can be attributed to a big dip in the jet stream, which is the fast moving river of air high up in the atmosphere that divides cool air to the north from warm air to the south.  In the figure below, the dip in lines over the eastern U.S. shows a dip in the jet stream on Saturday, October 29th.  That dip is called a trough and the cool air from Canada flows south inside the dip. 

Daily Weather Maps

On the leading (eastern) edge of the dip in the jet stream, at the surface of the Earth, was a low pressure system off the Northeast coast with a trailing cold front that extended down through Florida and towards the Caribbean.  Below is a map showing the surface weather features on Saturday, October 29th. 

In the Caribbean, just off the tip of the Yucatan Peninsula of Mexico, the remains of Hurricane Rina left a large amount tropical moisture right at the end of that cold front.  This tropical moisture flowed north, ahead of the cold front.  Once this tropical moisture reached the area of low pressure, it was wrapped around the center of the low within it's counter-clockwise circulation. The tropical moisture hit the cool air on the backside of the low and formed snow.  Lots and lots of snow!  That is what created this pre-Halloween snowstorm.  The storm was also called a Nor'Easter, not because it hit the Northeast but because the position of the low on the coast brought northeast winds to the area.

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