Sunday, June 17, 2012

The Nor’easter the classic winter storm of the Northeast

A blizzard aftermath

The last time a classic Nor’easter hit the Northeast Coast of North America was during the Blizzard of 2006.  Although this storm was extratropical in nature it formed an eye just as a hurricane does.  The center of a snowstorm like this stays just off the coast of New England.  The heavy snow stays on the Northwest quadrant of the storm.  The limiting factor as to how much snow depends on the amount of moisture the storm picks up on its way north from its birthplace in the Gulf of Mexico.

A Nor’easter becomes a blizzard when certain conditions are met, the temperature must be colder then 20˚ F.  At the same time the wind velocity must exceed 35 MPH.  It appears that the storm plodding its way up the East Coast of North America on Dec.19, 2009 meets these criteria, and will be a blizzard.  The weather forecasters have already dubbed it to be one.

A storm like this has its start when a cold wave comes down along the front range of the Rocky Mountains and collides with warm water coming north from the Gulf of Mexico.  The cold air plunges down, and its leading edge turns to the left behind the warm air.  This produces a counterclockwise spin in the atmosphere that forms a Low Pressure Center, and a new storm is born.

The storm then comes out of the Gulf of Mexico and across Florida where the northward flowing warm waters of the Gulf Stream propel it northwards.  At the same time the Gulf Stream keeps pumping more moisture into the storm causing it to contract in upon itself until under the right conditions it can form an eye like a moderate hurricane.

It often requires the merger of several small storms coming together that were formed by the same mechanism to cause the formation of a Nor’easter.  The storm usually forms completely over the ocean east of North Carolina.  By the time they have reached the Midatlantic Coast they are fully developed and can ravage the coastal states and provinces as far north as Newfoundland.

The storms follow the Gulf Stream northwards along the northeast coast until they pass Newfoundland and vanish into the North Atlantic where such storms have been known to linger sometimes for weeks.

It is when the storm’s center crosses the 40 and 70 degree intersection that we get the most snow.  If the center of the storm is inside this intersection we will have snow changing to rain, often an icestorm.  If it is further out in the Atlantic Ocean the precipitation is lighter, and we might just get a dusting.  If the storm passes to our west we will receive just rain with warm southerly winds.

Although they are most common during the months having an “R” in their names a Nor’easter can occur at any time of the year that the conditions for their formation is met.  They are capable of producing prodigious amounts of moisture on land from the moisture they pick up over the Gulf Stream, and deposit it on land as either rain or ssnow.

These great storms follow a cycle of about twenty years according to a phenomena called the “Arctic oscillation>”  When this weather phenomena is on its positive side as it has been recently the airmass moves quickly enough so the storm is unable to draw down large masses of cold Arctic air upon which it feeds.  If we are in the negative side of the oscillation the air masses move more slowly, and the storm is able to feed on the Arctic air and thereby intensify.  It appears that we may be coming under the influence of the negative side of the Arctic oscillation and can expect colder and wetter winters.

These storms differ from a hurricane that feeds on warm tropical air; they feed rather on cold Arctic air.  There is always a cold mass of air to their west upon which the storm feeds.  How intense a storm is apt to develop is a function of the difference in temperatures the two air masses.  The greater this difference is the stronger the storm.   

The name for these storms is derived from the apparent direction the wind comes from when it is affecting the northeast coast of North America blowing predominantly from the northeast.  It shifts to the northwest after the center of the storm has passed you.  The name Nor’easter comes from the way the old compasses were laid out, and the name Nor’easter goes back to the days of early exploration by the Europeans of the New World.  The earliest use of the word was apparently 1538.


Nor’easter, Wikipedia,'easter

Nor’easters, The Weather Channel,  

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