Tuesday, February 25, 2014

What is causing the second half of winter 2013-2014 to behave like this?

I've been getting a lot of personal messages  on my Facebook weather page.... . What's up with this never ending pattern?  Is the cold winter caused by manmade global warming?.   

As I write these words, temperatures across the Northeast are plummeting. Our old friend the Polar Vortex is back , bringing with it brutal cold. 

As I predicted in my 2013-2014 winter outlook. This year would be a tail of two winters, the first half being mild and a lot less  wintery, the second would be much colder than average and very wintery, with coastal and clippers keeping us hopping. This is indeed how the winter turned out. With the current pattern, even winter diehards are becoming weather weary.

So what is causing this pattern?

Global warming activists in academia and the media are now seeking to link record-breaking cold to manmade global warming. There is no  meaningful scientific or historical link correlating, our current weather pattern to global warming. There are wild claims on both sides of the global warming debate. Junk science just clouds the issue, both sides use it to support  their claims. Before we can go on we have to understand a few basic concepts.

Weather and Climate:


Weather is just about what's going on in the atmosphere at a certain time and place.  Weather deals with Low pressure systems, high pressure systems,  temperature, humidity, precipitation (rain, snow, sleet, and hail), and of course wind. Weather deals with a short time scale, hours, days, weeks.  


Climate,  is just the average weather characteristics of a particular region.  Changes in climate occur over a much longer time scale than weather.  years, centuries, and even millennia.  The Earth has seen great changes between ice ages and warmer periods in the past.

The Sun, oceans and the atmosphere are linked in a complex web. It is these three things that cause weather on Earth.  to one another and are responsible for Earth's weather and climate.  The oceans help to regulate temperature in the lower part of the atmosphere.  The atmosphere is in large part responsible for the circulation of ocean moisture and heat. It's the interactions between  oceans, land, the Sun, and the atmosphere, that create our local weather.  

Pattern recognition is a very important skill when it comes to the science of meteorology. As I've said a number of times, I'm a big believer in concentric patterns, be it weather or other things in nature and across the universe.  These cyclical weather patterns can be months, a few years, decades, or even longer. Mankind hasn't been around long enough to recognize all of these patterns, detailed records of weather and climate only go back a few hundred years.  One just can't take a few storms or a few seasons and say global warming is or isn't causing something. We need to give real science time to figure it out.  

Here are two links that go into this in more detail. The first is a link to a post I did on manmade global warming. The second is by Prof. Stephen A. Nelson,  of Tulane University, and deals with  the Ocean Atmosphere System.

First Link

Second Link

So the bottom line is, on earth it's the ocean that plays the most  important role in shaping our climate and weather patterns. This is where teleconnections come in.

Teleconnections, Jet Stream, and the Polar Vortex:


Teleconnections are what control the jet stream and precipitation patterns. There are several Teleconnections across the Earth. I will only briefly explain the four that have the most influence on weather in North America.

The Pacific/North American pattern (PNA):

The PNA  is a teleconnection that governs weather from around China, to the East Coast of the US, every month except June and July. The air masses over the warm waters of Hawaii and in the cool waters of Alaska's Aleutian Islands start a circulation pattern that sweeps east into North America. There the pattern interacts with a high ridge of air over the northern Rockies and a deep trough over the southern states.

When the difference in air pressure between two designated points within an atmospheric oscillation is great, conditions are described as "positive." When the difference is low, conditions are "negative." The PDO is talked about a lot in discussions about climate change since its state can significantly affect the global temperature and the occurrence of some types of weather events. It affects the favored El Nino-Southern Oscillation (ENSO) state, the cold PDO favoring more frequent, stronger and longer lasting: La Ninas, and the warm phase more frequent, stronger and longer lasting El Ninos.

When the  PNA turns negative, the airflow becomes more directly west-to-east.

A positive PNA carries tropical moisture into British Columbia, and the United States ends up with cold and stormy weather in the Midwest and Southeast; cold in the East and warmth in the West; and tornadoes—and even snowstorms—along the Gulf Coast, as blasts of polar air meet warm, moist air in the South.

A negative PNA carries diminishing amounts of moisture eastward from California, resulting in cold and snowy weather in the West; rain and snow in the plains; and warm and relatively dry weather in the East.

The North Atlantic Oscillation (NAO):

The NAO affects the eastern United States. This teleconnection sits between the cool atmospheric low over Iceland and the warm high over the Azores.

In winter, a positive NAO causes Atlantic storms to veer north, and warm, wet winters to occur in the eastern United States and Europe. Northeastern Canada tends to be unusually cold. In summer, a positive NAO means fewer tropical storms and hurricanes striking the East Coast.

In winter, a negative NAO forces cold air into the eastern United States, and causes heavy rains in southern Europe. Northeastern Canada is generally warmer, and areas around the Great Lakes tend to have a cooler, wetter spring. Studies of a negative NAO in summer have proved inconclusive.

The Arctic Oscillation (AO):

The AO like the other teleconnections has two phases. The positive phase is represented by low pressure over the polar region and high pressure at the mid-latitudes. The opposite occurs during the negative phase. The AO has a lot to say about storm tracks in North America. When the AO is negative it allows the cold air in Canada to drop south into the United States

The EPO (Eastern Pacific Oscillation):

The EPO is located in the eastern Pacific, and is  similar to the NAO.  , It's an alternating pattern of high and low atmospheric pressure, The EPO helps determine the pattern of the jet stream moving from the Pacific across North America. The negative phase corresponds to widespread cooling over central and eastern North America and the positive phase to warming.

The Jet Stream:

I'm sure most of you have heard of the jet stream,  It's the driving force in our weather. When it comes down to who sees what kind of weather, all comes down to the position of the jet stream.

Basically the Jet is just an river of air thousands of feet above us that meanders around the globe. When one looks at the charts of the 300mb through the 100mb level the jet stands out. You will see that it waves ( bends) up and down, these are the troughs, ridges, and crests. You hear about in forecast on my weather page and on TV.

A trough typically brings active weather to a region. It also brings cooler air most of the time, too. A ridge is the opposite - it normally brings nice, sunny, and warm temperatures to an area.
The placement of the Jet is especially important during the winter.  during this season it normally moves into a position that divides the U.S. into two. During winter the jet is the reason for all the temperature swings. When the jet moves south during the winter season, the storm track becomes more active. 

The jet stream has a lot to say about that the polar vortex does and where it goes.

The polar vortex (PV):

The PV is an area of  low pressure that usually circulates counter clockwise above the Arctic Circle. Something like a hurricane of very cold air. During the summer months the PV will weaken, and during the winter it will strengthen  Usually  during the winter months it resides up there, but sometimes the PV will weaken and parts of it will break off and move southward and bring cold air outbreaks into the U.S.


                                                   Typical position of the Polar vortex

                                                What the polar vortex looked like in January


All the things I've just showed you, are all the pieces that have caused the Winter of 2013-2014 to behave the way it has.

So what the bleep is going on?

Back in late fall there was an increase in rainfall across Indonesia. Normally this would be attributed to a condition known as La Nina. This is the opposite of the more famous El Nino, and is simply a natural change in the temperatures of the Pacific Ocean.
However, although the temperatures of the waters around Indonesia were above average this year, as they would be during a La Nina event, the rest of the Pacific was unaffected. The conditions were therefore not classed as La Nina. Instead we had what is called a neutral ENSO year.

The heavy rain continued over Indonesia and the rest of the western Pacific throughout December and January. The warm seas ensured that vast amounts of water were pumped into the atmosphere, some of which was picked up by the jet as it moved towards the west coast of North America.

In a more normal year,  the jet stream will meander north and south. The  weather systems will move north and south with it.  However, if it sits over one place for a prolonged period, then the area below the jet stream will end up far wetter than usual, but another region to the north or south will remain far drier.

This is what happened to the jet stream over the Pacific this winter. It usually flows from the western Pacific to the northeast of the USA, but in December and January, it was deflected a long way further north than usual. This was bad news for North America.

This winter season, we have seen a ridge of high pressure out over the West Coast, extending north toward Alaska. Also, we've seen a deep trough over the eastern part of the U.S.  The position of the jet forced storms up over the ridge, avoiding the West Coast, this has led to the severe drought that California is seeing.

With the jet positioned the way it was, these storms became Clippers that moved south into the Midwest, Northeast, and Mid Atlantic States. The jet also allowed for the waves of Arctic air to sweep south into the eastern part of the lower 48.

The Jet has also been a player in the PV this season. Last Summer and Fall, Alaska saw very warm temperatures and saw quite a few thunderstorms. This was because of the West Coast Ridge (remember all the moisture from Indonesia moving east).

The warm moist air from the Pacific Ocean was forced up into Alaska. The warm temps in Alaska and around the Arctic, caused sea ice to melt. The amount of sea ice has a lot to say about the behavior of the PV. 

When there is a lot of polar sea ice, the PV is strong. However, when Arctic sea ice volume is less, the PV weakens . This is the reason the PV is weaker in the summer time and stronger during the winter time. And as I said, above when the PV is weaker, pieces of it will break off and head south.

The jet stream this winter has been highly active, and there are no signs of that changing. At the moment it is set up in such a way that the active weather will stay across the eastern two-thirds of the nation while the west stays relatively quiet. This is why I think March will be colder than average. I think March will see quite a few Clippers and the occasional Coastal.

Well that's about it.... I tried to make a complicated process easy to understand... I hope I was able to do that for you. As always I will answer any question that you might have on this post. either leave a comment on this blog. or post it on my Facebook weather page, you can find the link on the right side tool bar.

I hope you found this enjoyable and educational.  


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