DROUGHT WATCH IN EFFECT FOR NEW JERSEY

It is once again that time of year where snow lovers across the Northeast and Mid Atlantic have one question and one desire.  Will my back yard see plenty of white or brown mud?  

Before I go into detail about my winter forecast, I want to explain how I developed and produced the theory for this winter’s predominant characteristics.  

In today’s long range forecasting, the ability and skill of the long range forecaster has dramatically increased over the past few decades.  Think back to the 1970’s and consider there was no internet, no readily available satellite data.  No way to watch the developing ENSO states or look at the temperature and pressure changes of the stratosphere.  With all this new technology, we have seen an explosion of new or revised teleconnection indices and a better understanding of how each index can have an impact on certain regions of the globe.  For example, any person can now look at over 13 different index readings describing the various states of the atmosphere.  How was do all these different indices mean when they play off each other?  That is the issue at hand when many forecasters and weather enthusiast start to get stuck on look at the PDO and only the PDO or just the ENSO state.  What we all must try to grasp is how all of these synoptic features work in concert with each other.  After all, the atmosphere is not a stand alone model.  All features have direct and indirect impacts throughout the Earth.  

Noting that important aspect of understanding the atmosphere, I will attempt to tie together the developments and trends of Pacific pattern, stratospheric temperature and height anomalies and trends, and the trends and develops of the Atlantic pattern.  Also, by learning from mistakes from previous years along with this year, I will attempt to give a view of the winter pattern along with a few various storm tracks that I think are likely.  

So get some hot chocolate or coffee and lets take a peak into the winter of 2008/9!

Top Of The World

Last year I learned an important lesson on how the stratosphere can play a huge role in determining how the winter will play out over North America.  This time, I started my winter forecast at the stratosphere over the North Pole.  This is why I waited until the end of the month to post this winter forecast.

This year’s temperatures to this point are much warmer than last year and have not shown any hint of going extremely below normal as last year.  This observation is extremely important.  

When the stratosphere is warm, the layer pushes down on the troposphere.  This action compresses the lower atmosphere and produces a favorable environment for cold air to develop.  This is a very basic explanation, however I want everyone to keep this in mind.  

This year, the trends at the stratosphere in late October have kept the coldest air over Siberia, while the warmer air temperatures have been found over northern Canada.  This would suggest a potential for warmer conditions at the surface over Siberia and a more likely potential for a ridge to be sustained at 500 MB over this location.  

Meanwhile, the warmer air at the stratosphere over Canada would support a cold air mass at the surface and a negative Arctic Oscillation.  

So we start with the idea this winter that the upper atmosphere will be more conducive for a negative AO over North America and better support for a ridge over Siberia.  This would lead to a sustained trough over central Europe and eastern Asia.  I also hypothesis that the coldest air over northern Hemisphere will be over North America this year and not over Asia like last year.  A strong reminder that last year when the warmest stratospheric temperatures were over Asia, that China had one of the worst winters in history for that region.  

The observations over the stratosphere will be extremely important going into November and any substantial fall of temperatures below normal will drastically alter the winter forecast.  However, at this time I have not seen any trend that would indicate the extreme conditions from last year nor any sign of the drastic cooling from other years.

The Eastern Pacific Oscillation:

Now I’m going to take another step forward.  With the assumptions I have laid out above, we can assume that a ridge will be a constant feature over Siberia, which would support a trough over the eastern coast of Asia.  

The trough over eastern Asia is also supported by features at the surface, namely sea surface temperatures.  The sea surface temperature anomalies along the eastern coast of Asia are all above normal, which suggest an impressive area of rising air.  With the idea that a constant clash of the relatively colder air over central Asia interacting with the warm waters over the western Pacific, there will be a high potential for strong cyclogenesis off of eastern Asia and over the Japanese coast line.   

The potential for a constant trough position over eastern Asia and Japan produces a negative EPO index.  When the EPO index falls into the negative, a trough is the result over the eastern United States.  

Due to the high potential for a constant “clash” of strong air masses over this region of the world, I hypothesis that we will continue to see a strong negative EPO through this winter, which will be an important indicator on when to expect cold out breaks and winter storms.

THE ENSO AND THE PDO:

The most important development in the Pacific this year is the lack of a defined ENSO phase as the Pacific features neither an El Nino nor La Nina.  The fact that there will be no driving ENSO impact on North America means that other key features like the Arctic Oscillation, the North Atlantic Oscillation, and the Eastern Pacific Oscillation will be more important features to keep an eye on.

However, the atmosphere is still feeling the effects from the strong La Nina experienced just a few months ago.  This has produced a strong negative PDO, which will be a very important feature for North America.

However, before we go into the PDO, let’s look at what is occurring right now around the  Northern Hemisphere.  This year we see a lot stronger blocking features setting up over the northern Atlantic and over the Pacific.  In years where the Pacific jet stream blasts through the Pacific and into the western coast of North America, these blocking features can not materialize.  With weaker trade winds this year, the ability for the Pacific jet stream to intensify will be diminished.  

What does the negative PDO suggest though?  

Currently, the PDO appears to be entering into a “cool” phase which can last up to 20 years.  The cool phase of a PDO has an underlying La Nina impact on the entire upper level pattern of the Pacific and North America.  

Under the cool phase of the PDO, the sub tropical jet stream does become more active, which will lead to the potential of several disturbances cutting through the Gulf Coast and over the Southeast.  The PDO state will be a key factor in my opinion however, I wanted to compare what the atmosphere looks like in a cool phase of the PDO and a more “active Atlantic” period.

THE ATLANTIC MULTIDECADAL OSCILLATION (AMO)

The AMO, like the PDO, is a 30 to 35 year phase of warmer/cooler waters over the Atlantic ocean.  In a warm phase, which we have been in since 1995, the potential for more major hurricanes increases due to above normal water temperatures over the Atlantic.

A positive AMO produces a strong Gulf Stream along the eastern North American coast line, which produces a strong thermal gradient.

When I started this forecast, I wanted to see if there is any link to the influence of stronger tropical disturbances and blocking over the North Atlantic.  I think I found that link in this case.  

When the AMO is positive, the potential increases for more storms over the western Atlantic and a higher potential for blocking.  The blocking usually comes in the form of a negative NAO.  

The pattern of a positive AMO tends to force tropical disturbance towards the north in the late fall and winter months, which can enhance the upper low at the 50/40 bench mark.  Thus the connection between an active tropical Atlantic and the pattern in the north Atlantic.  This is only a theory, but I think this will play out to be an important influence this year given the lack of a strong Pacific jet to break up the blocking over the northern latitudes. 

A NEGATIVE PDO AND A POSITIVE AMO IMPACT

When combining the influences of a negative PDO regime (active subtropical jet stream) with a positive AMO regime, the result is a high potential for precipitation along the East coast, including a higher potential for Nor’ Easters.  Usually, the trend in these periods is for more coastal storms, which can lead to a lack of precipitation over the Ohio Valley through the Great Lakes.  

In a negative PDO, positive AMO environment; a trough is more likely along the east coast with a higher potential for cyclogenesis due to the strengthening thermal gradient.  The warmer air over the Gulf of Mexico and Atlantic coast will produce strong rising air currents at the lower and mid levels, which will produce a favorable environment for cold air to rush towards the coast line.  

The year that best matches the current stratospheric conditions, PDO conditions, and AMO conditions continues to be 1960/61, which is one of the top 10 snowiest winters in the forecast area.  

The North Atlantic Oscillation

The phases of the North Atlantic Oscillation (NAO) is going to be extremely important this winter.  The North Atlantic Oscillation, when negative, produces a strong blocking regime over eastern Canada and the north Atlantic.  When negative, strong Canadian high pressure tends to lock over New England, produce strong cold air damning.  Meanwhile, low pressure systems along the coastal plain tend to move slower and closer to the coast.  The combination of the cold air along the coastal plain and the warm waters of the Gulf Stream produces a strong thermal gradient that can lead to significant intensification of the surface lows.  

This year, I believe we will see a negative NAO regime.  The positive AMO pattern combined with a negative Arctic Oscillation will lead to a favorable negative NAO pattern.  The potential for strong storms to develop off the East coast will support the potential for those storms to build a strong ridge over Greenland and eventually northeastern Canada.  

The idea here is that the constant feed back of this pattern will lead to a sustained block over northeastern North America.

The Arctic Oscillation:

The Arctic Oscillation this October is extremely positive right now, which is great news for winter lovers over the East.  A positive Arctic Oscillation in October or late fall tends to be followed by a volatile, negative baring Arctic Oscillation through the winter month of December through March.  The data from 1950 to 2000 is rather impressive.  In just taking years where the AO was positive in October, the following winter months had a negative AO 54% of the time.  I wanted to take this a step further, so I limited the data to years that corresponded to a negative PDO phase along with a positive AMO phase, which was last seen from 1950 to 1965.  In those years a positive AO was observed in October 9 times and 8 of those observations was followed with a negative, volatile AO for December through March.  That’s 89% of the time.  Finally, I took one more step and only took years where there was a neutral ENSO, a negative PDO phase, and a positive AMO phase, which had 3 years of a positive AO in October.  Two of those years had been followed with a strong negative AO.  

So given the data and climatology, I think there is a clear signal that there is a highly probable chance of a negative Arctic Oscillation this winter.  When the Arctic Oscillation is negative, there is a more favorable environment for a negative NAO.  

I should also note that a positive AO in October over northern Canada is more conducive for snow growth and building the cryosphere over northern Canada.  The more snow that can build over Canada now, the colder the air masses that can develop for December, January, February, and March.

The pieces are coming together.

Combining All The Pieces:

Now I think it is time to combine all the pieces and put this forecast together.  

I believe first that the stratosphere this winter will be much more favorable for high latitude blocking and specifically supporting a negative phase of the Arctic Oscillation and North Atlantic Oscillation this winter.  Given the trends this late fall of the coldest stratospheric temperatures over Siberia and western Asia, there will be strong support for above normal temperatures and a persistent ridge over the north-central Asia.  

The strong ridge over central Asia, which is supported by stratospheric conditions, will also lead to the development (in fact this has already been seen the past month) of a constant negative Eastern Pacific Oscillation (EPO).  A negative EPO is a strong indicator and teleconnection of a ridge over the western coast of North America and a trough over the eastern third of North America.  

The negative PDO regime strongly suggests a more active sub tropical jet stream.  Due to the blocking that will be supported at higher latitudes, we can expect to see a defined split in the Polar Jet stream, with a great deal of moisture and disturbances moving through Mexico, the Gulf of Mexico, and into the Southeast.  We have already seen hints of the developing sub tropical jet stream this fall when looking at the water vapor satellite images the past few weeks.  

The negative PDO regime along with the positive AMO phase has been shown to support enhanced high latitude blocking and increase cyclogenesis off the East coast, specifically from the Carolina coastal waters towards the Canadian Maritimes.  

The warm or positive phase of the AMO also exhibits more energetic tropical disturbances, which enhances mid and high latitude low pressure systems.  The enhancement, in theory, should also strengthen the upper low over the Northern Atlantic which would build the ridge over Greenland and thus produce a strong negative NAO structure.  

The positive AMO phase also produces a stronger thermal gradient along the East coast, which leads to more intense coastal storms should other factors contribute to favorable atmospheric conditions.  

The closest year that matches all of the described ingredients going into this winter is 1958/59 and 1960/61 although neither is a perfect match.

Expected Storm Tracks:

No winter has one constant storm track as pattern usually relax after a period of significant amplification.  As a result, I wanted to cover a couple of basic patterns that I think we will see from November on through March for 2008/09.  

+PNA, -NAO Pattern:

This pattern keeps the subtropical jet stream suppressed over Mexico, but can have some interaction with the northern branch of the jet stream over the Gulf Coast and Southeast.  Disturbances in this pattern have the potential to move through the CONUS and specially over the Southeast much slower, which gives ample time for the potential of phasing or optimal development of conveyor belt structures in the storms.  

The strong blocking over northern Canada supports strong cold air damning along the Eastern sea board, which gives the Northeast and Mid Atlantic the most optimal potential for heavy snowfall.

The negatives with this pattern is that timing is essential with the sub tropical and polar disturbances.  In some cases, there will be times where the trough axis may be too far east or west for an optimal storm track for the I-95 corridor.  

-PNA and + NAO patterns

This pattern can be expected generally after a strong -NAO phase in the pattern.  In this pattern, the eastern United States will be able to warm dramatically.  The – PDO La Nina like influence on the overall pattern will take hold and allow for the weak ridge that will be present through the winter over Cuba to build throughout the Northeast.    The storm track will usually begin over southern California towards the central Plains and off towards the central Great Lakes.  This type of storm track usually will “reload” and amplify the blocking mechanisms over the higher latitudes and allow for a negative NAO to redevelop.  

I don’t expect this type of pattern a lot, but the most likely time period for this set up will be in early to mid January.

Sub Tropical Disturbance Madness Pattern:

This pattern is what will likely drive models, meteorologist, and winter weather enthusiest completely mad this winter.  In this pattern, a strong sub tropical disturbance will drive under the strong PNA ridge in place over the western Canadian coast.  The negative NAO blocking structure will continue to be in place, which will support a persistent trough over the eastern third of the United States.  This means that disturbances from the northern branch, like clippers for example, will still continue to drive from the northern Plains towards the Mid Atlantic coast along with fresh Polar/Arctic air.  

The question with this pattern is how does the upper low or strong disturbance from the southern branch interact with the northern branch of the Polar jet stream.  There are several possible out comes with this type of pattern.  Naturally, the most popular and highly hoped for will be the “perfect” phase, where the two disturbances remain separate at least until the trough axis get past the Mississippi Valley.  Then a monster storm is formed with fresh cold air over the forecast area and a moisture loaded low pressure system moving right into that cold air.  

However, there is also just a good of a chance that one disturbance will “kick” the other disturbance to the east with no such storm at all.  Or the phasing ends up canceling the disturbances out due to the negative NAO being too strong, thus leading to strong subsidence down through the Mid Atlantic.  Then there is the nightmare of snow lovers that there potential monster snow storm gets “pulled” to the northwest by the northern branch thus turning a promising snow event into a wash out.  In this set up, all of these scenarios will be possible and you can bet the model guidance will be jumping like a hot potato trying to iron out the details.  

Cold, Dry, And Boring:

This pattern is another transition pattern, but in the cold regime.  This pattern will take place when a strong Arctic or Polar high pressure will build down through much of the Eastern two-thirds of the United States.  In this pattern, the negative NAO will be strongly negative, but will be trending back towards neutral.  This pattern will exhibit fast moving “clipper” low pressure systems take can produce the occasional surprise moderate snowfall and the even rarer heavy snow fall over localized coastal locations.  

Overall though, this pattern is cold and dry with characteristics of dangerous wind chills and possibly record setting low temperatures.  This pattern is usually followed by the active pattern described +PNA/-NAO.  

CONCLUSION:

This winter will be the first winter in which we will be in a cool phase of the PDO and a warm phase of the AMO, which will likely lead to some very interesting winter storms this year.  High latitude blocking and a split Polar Jet stream will be the many themes this winter along with the question of timing disturbances with each event.

I expect that the New York City and Philadelphia metro will have a winter with slightly below normal temperatures overall from December through March.  I expect a period of brief warm conditions in early January followed by a return to cold conditions for late January through March.  There is a high potential for above normal snowfall for both the New York City and Philadelphia metro areas this winter.  This year will also exhibit more coastal storms and an important influence on coastal front structures for each coastal storm event.  In other words, cold air damning processes will be very important in the meso-forecasting aspect of these storms.  

I don’t like to give snow fall totals for specific locations cause I think these are a shot in the dark to be honest.  However, for the sake of avoiding the questions I’ll get ahead of time, I think that Philadelphia and the New York City metro areas will average 35 to 50 inches this year, on the lower side of that range along the coast and higher over the interior.