Sunday, January 18, 2015

What's up with Winter?

We’re just a few days past the halfway point for meteorological winter.

So far across the major cities of the Northeast, from Philadelphia to New York and on up into Boston, have had a very lackluster winter.  Across the Northeast snow lovers are flustered.  Seasonal snow totals are lagging behind the norms. There have been some minor storm systems here and there, which have produced minor or moderate amounts, however, the major storm is yet to be seen. 

Snow depth in Washington DC, New York City, and Boston is at zero. In fact, there is little to no snow from Maryland and eastern Pennsylvania, right up through Southeast New York State and much of southern New England.

For the last 6 weeks the pattern has favored inland runners or coastal huggers.

Boston's total snowfall as of the 16th of January was just 4.7 inches, well below the average of 15.8 inches on that date.   New York City (Central Park) has seen only 3.2 inches  so far this season ,  compared to the average of 7.9 inches. It's the same story for Washington DC , so far only 2.3 inches , which is half of the average of 4.7 inches. Philadelphia is 4.2 inches below average.

The lack of snowfall is also effecting areas much farther inland. Central New York  is having a snow drought , Central and western Pennsylvania as well.....cities like Pittsburgh, are also lagging behind. Parts of the Midwest are also experiencing less snow than average.

The northern and Central Tug Hill has seen near to above average snowfall.... as has places like Buffalo off of Lake Erie....but for the Southern Tug Hill it's a different story, they too are below average in the snowfall department. 

The snow drought isn't only a Northeast problem, the northern Plains and Cascades are also seeing a lack of snowfall.

The winter season of 2011 was one of the snowiest on record and 2012 was one of the least snowiest.  This season we've seen a few minor to moderate storm systems, but nothing has produced anything major.

So what is going on?

So why the lack of snow?  It has been cold this winter, but the pattern hasn't allowed the cold and storms to work together to produce a major snow for the Mid Atlantic and Northeast.

We had quite a few nor'easters in the Fall, but there is no doubt there has been a real lack of strong nor’easters for the last couple of months.  The pattern as allowed for Cutters, Inland Runners, and coastal huggers, that have brought more rain than snow.

One of our problems has been the  North Atlantic Oscillation ( NAO).  The NAO index “is based on the surface sea-level pressure difference between high pressure in the Subtropics and the Subpolar low pressure. The NAO has a lot to say about how air is moving across the Atlantic. When the NAO is negative we have generally colder and wintery weather in the Mid Atlantic and Northeast.  A negative NAO allows for  higher pressure to setup around Greenland and Iceland. The so called Greenland block allows the jet stream to slowdown, the customary westerlies become more dynamic. The jet stream is a band of strong air currents that encircles the hemispheres (one in each) several miles above earth’s surface. So when a blocking high is parked east over Greenland, the arctic air is pushed away from the arctic and into eastern Canada and East Coast.  With the slower pattern there is more time for storms to interact with the cold air, so that we can see major snowstorms. 
The NAO this winter has trended positive to very positive......Some of you might be saying, but we've had cold air for quite a few weeks now. I thought you said a negative NAO brings the cold air?  In answer, I say meteorology is quite complex and many things in the atmosphere effect our weather. For the answer to this question, we have to look elsewhere.   

Another problem has been the highly-amplified atmospheric pattern over North America. Highly amplified flow  is frequently associated with anomalous weather. The current pattern has hung around since last winter...and is one of the reasons for the active number of tornadoes in the Mississippi Delta, Pennsylvania, and New York State last Summer.  Another similar pattern (though much longer lasting) was responsible for Dust Bowl drought In the 1930s. 
We've had the ridge over the Eastern Pacific and western North America, With a strong trough over eastern North America.  This  large scale pattern produced relatively little rain over the western U.S. and allowed  for  rain over the southern Plains and eastern U. S. This is because storms moving across the Pacific are diverted north by the ridge.... moving up over Alaska and the Northwest Territories in Canada. These storms slide down the trough bringing precipitation to the Midwest, Mid Atlantic, and Northeast.  The overall jet stream pattern is the reason for all the Clippers, Inland Runners, and Coastal Huggers..... The Clippers pull down colder Alaskan and northern Canadian air behind them..... So we have Cold air in place.  


The predominate pattern has been the Clipper pattern....but once in a while, we've switched to a Split Flow pattern.    

A split flow is named that because the two branches of the jet stream are more or less separate. One branch extends south across places like the Texas panhandle and moves over the Southeast U.S.  The other branch is further to the north, extending out of Canada and moving into the northern U. S. The pattern can be very active on the northern stream and southern stream. But in-between it's fairly tranquil. Because the two streams don't interact....there is no storm phasing.  



 The  lack of a negative NAO leads to no upstream blocking, so there is nothing to slow down the storms to allow for much in the way of the phasing needed for  major coastal storms. It's is also helping keep the storms closer to the coast, and not going near the 40/70 benchmark. The benchmark is located at 40 degrees north latitude and 70 degrees, southeast of Montauk Point on Long Island.  Most major East Coast snowstorms will pass over or near this 40/70 benchmark . It's the  ideal track for a major nor'easter.

El NiƱo where is it?

El Nino, an abnormal warming of surface ocean waters in the eastern tropical Pacific, is one part of what's called the Southern Oscillation. The Southern Oscillation is the see-saw pattern of reversing surface air pressure between the eastern and western tropical Pacific. I said in my Winter Outlook, that this would be a weak El Nino.  It's looking at my prediction for even a weak El Nino was overdone. The sea surface temperature anomalies in the tropical Eastern Pacific, are starting to fade,  right now there isn't much in the way of warming in the eastern part of the  Pacific.  So it won't have a significant impact for the rest of winter 2014-2015..
 The Good news is the cold air pattern we're in looks to continue...... It also looks like the NAO will be trending more in the way of negative as we finish out January and go into February....Maybe we can get something phasing in the cold air....remember it would only take one major snowstorm to reverse our lack of snow.