Winter 2012-13 Preliminary Thoughts & Further Discussion

The Winter of 2011-2012 was a winter many of us will never forget . Essentially this winter started off with a BANG with delivering a Historical East Coast Blizzard across portions of the Northeast..delivering 6.8 inches of snow to Allentown Bethlehem Easton Airport on October 29th. This storm had set all kinds of records and many of us thought that this would set the stage for a snowier and colder winter. After all it got off to an early start.
However as winter went along we realized that the Alaskan Vortex was to strong and that blocking was not going to make it down to the lower atmosphere or surface which is where we need it to occur. So we ended up with a very warm winter and snowless winter instead. The winter of 2011-2012 ended up a La Nina Enso status. Matter of fact it was a two year La Nina. Since that time we have now gone to a Neutral Status but the question is where do we go for the winter ahead? This leads us to ENSO status and where it looks to be heading.
The El Niño-Southern Oscillation (ENSO) is a naturally occurring phenomenon that involves fluctuating ocean temperatures in the equatorial Pacific. The warmer waters essentially slosh, or oscillate, back and forth across the Pacific, much like water in a bath tub. For North America and much of the globe, the phenomenon is known as a dominant force causing variations in regional climate patterns. The pattern generally fluctuates between two states: warmer than normal central and eastern equatorial Pacific SSTs (El Niño) and cooler than normal central and eastern equatorial Pacific SSTs (La Niña).
Often, sea surface temperatures (SSTs) are used to identify this oscillation, but it is important to understand that changes in sub-surface ocean temperatures are the first to respond to an oncoming change in the ENSO phase. For instance, when ENSO is transitioning into a warm phase the sub-surface temperatures begin to warm above average, while a shallow layer of near average temperature remains at the surface. Eventually, the surface ocean temperatures will respond to the warming of the sub-surface temperatures, and a warm phase of the ENSO cycle ensues. The same cycle occurs, only opposite, for the cool phase of ENSO. When temperatures in the ENSO region of the Pacific are near average it is known as ENSO neutral, meaning that the oscillation is neither in a warm nor cool phase. Typically, atmospheric patterns during ENSO neutral are controlled more by other climate patterns (NAO, PNA) that vary on shorter timescales;



According to the two images above it looks like we are heading into an El Nino for the winter ahead. What exactly is an El Nino?

El Niño (Warm Phase)
The warm phase of the ENSO cycle features warmer than normal SSTs across the central and eastern equatorial Pacific
along with:
Weaker low-level atmospheric winds along the equator
Enhanced convection across the entire equatorial Pacific
Effects are strongest during northern hemisphere winter due to the fact that ocean temperatures worldwide are at their warmest. This increased ocean warmth enhances convection, which then alters the jet stream such that it becomes more active over parts of the U.S. during El Niño winters.
So lets look at the history of past El Ninos, the years they covered and whether they were warm or cold. First the years:
Previous El Niño Years
1902-1903
1905-1906
1911-1912
1914-1915
1918-1919
1923-1924
1925-1926
1930-1931
1932-1933
1939-1940
1941-1942
1951-1952
1953-1954
1957-1958
1965-1966
1969-1970
1972-1973
1976-1977
1982-1983
1986-1987
1991-1992
1994-1995
1997-1998
2002-2003
2006-2007
2009-2010
We will look at the warm years first in which there were 12 warm years.












Now lets take a look at the colder years..














Now..we can see that the cold years slightly outweigh the warm years with 14 of the winters colder then normal across the east.
Things get a little more interesting when you narrow things down to El Ninos that followed La Nina's…

These are temperature anomalies for years that had an El Nino that was following a La Nina, the years that are included in it are: 1951-52, 1957-58, 1965-66, 1972-73, 1976-77, and 2006-07
So as you can see we have a colder outlook across the USA for el Ninos that have followed a La Nina.
However.. experience and knowledge also tells us that there are other factors that we have to look at ..
One of these factors it the North Atlantic Oscillation.
North Atlantic Oscillation (NAO)
The North Atlantic Oscillation (NAO) consists of two pressure centers in the North Atlantic: one is an area of low pressure typically located near Iceland, and the other an area of high pressure over the Azores (an island chain located in the eastern Atlantic Ocean). It is important to note that these two locations are most commonly used to measure the NAO, but studies have found that the pressure centers move around on a seasonal basis, and other locations have also been used for measuring this index. Fluctuations in the strength of these features significantly alters the alignment of the jet stream, especially over the eastern U.S., and ultimately affects temperature and precipitation distributions in this area. It is also important to note that the AO and NAO are two separate indices that are ultimately describing the same phenomenon of varying pressure gradients in the northern latitudes and the resultant effects on temperature and storm tracks across the continent.



Positive NAO
During a positive NAO there is a strengthening of the Icelandic low and Azores high. This strengthening results in an increased pressure gradient over the North Atlantic, which cause the westerlies to increase in strength. The increased westerlies allow cold air to drain off the North American continent rather than letting it build up and move south.
Above average geopotential heights  are observed over the eastern U.S., which correlates to above average temperatures
The eastern U.S. often sees a wetter pattern with stronger storms during the winter season in this phase due to increased upper level winds


Negative NAO
A negative NAO indicates weakening of both the Icelandic low and Azores high, which decreases the pressure gradient across the North Atlantic. This decreased pressure gradient results in a slackening of the westerlies. The decrease in the westerlies allows cold air to build up over Canada, and this combined with below average heights (troughing) over the eastern U.S. gives the cold air a greater chance to move south and affect the eastern United States.
Below average geopotential heights  are often observed over the eastern U.S. during the negative phase of the NAO, which correlates to below average temperatures
The eastern U.S. typically receives colder, drier air masses during the winter season in this phase
When the Icelandic low and Azores high are weaker, above average 500mb heights are located near Iceland, and below average heights near the Azores Islands. This results in a phenomenon referred to as high latitude blocking, which allows cold air to drain from Alaska and Canada into the U.S. and become entrenched, resulting in cold air outbreaks and below normal temperatures.

Positional Effects
Favorable positioning of the geopotential height anomalies within the negative phase of the NAO appears to enhance snowfall potential in the eastern U.S. When negative NAO anomalies are positioned such that an area of high pressure is located near Greenland and a polar vortex (area of low pressure) is somewhere near 50°N 50°W, we find an increased potential for winter weather along the U.S. east coast.
Atmospheric features in a “west-based” negative NAO disrupt the polar jet stream, causing it to buckle and move southward into the Southeast
Allows cold, Arctic air to be transported south and increases the likelihood of interaction between the northern and southern jet streams
Jet stream interactions often result in a combining of energy (phasing), which leads to rapid, intense surface cyclogenesis over the southern U.S.
Another area we need to look at is the Arctic Oscillation.


Arctic Oscillation (AO)
The Arctic Oscillation (AO) is a climate index of the state of the atmospheric circulation over the Arctic. It consists of a negative phase, featuring below average geopotential heights , which are also referred to as negative geopotential height anomalies , and a positive phase in which the opposite is true. In the negative phase, the polar low pressure system (also known as the polar vortex) over the Arctic is weaker, which results in weaker upper level winds (the westerlies). The result of the weaker westerlies is that cold, Arctic air is able to push farther south into the U.S., while the storm track also remains farther south. The opposite is true when the AO is positive: the polar circulation is stronger which forces cold air and storms to remain farther north. The Arctic Oscillation often shares phase with the North Atlantic Oscillation (NAO) (discussed below), and its phases directly correlate with the phases of the NAO concerning implications on weather across the U.S.


The next area we have to look at is the Pacific North American Oscillation index.
The Pacific/North American teleconnection pattern (PNA) is one of the most recognized, influential climate patterns in the Northern Hemisphere mid-latitudes beyond the tropics. It consists of anomalies in the geopotential height  fields (typically at 700 or 500mb) observed over the western and eastern United States. It is important to note that the PNA has been found to be strongly influenced by the El Niño-Southern Oscillation (ENSO) phenomenon. The positive phase of the PNA pattern tends to be associated with Pacific warm episodes (El Niño), and the negative phase tends to be associated with Pacific cold episodes (La Niña).

Positive PNA
The positive phase consists of above normal geopotential heights over the western U.S. and below normal geopotential heights over the eastern U.S. This correlates to ridging over the western U.S., and deep troughing over the east. The net result of the height field pattern in this phase is that it forces cold air residing in Canada to plunge southeastward, which results in below normal temperatures over the eastern U.S. and above normal temperatures over the western U.S.
In the positive phase, above average geopotential heights are seen over the western U.S., and below average geopotential heights are seen across the eastern U.S. This results in warm air moving much farther north than normal over the western U.S., while cold, Canadian air is forced southward over the eastern U.S. resulting in below normal temperatures.

Negative PNA
The negative phase features troughing and below normal geopotential heights over the western U.S. and ridging with above normal geopotential heights over the eastern U.S. The result is below average temperatures for the western U.S., and above average temperatures over the eastern U.S.
The negative phase of the PNA pattern features below average geopotential heights over the western U.S., and above average geopotential heights across the eastern U.S. This results in deep troughing over the western U.S., which allows cold air from western Canada to drain southward into this region. In the eastern U.S., warm, moist air from the Gulf of Mexico and the Atlantic Ocean is able to travel northward, often resulting in above normal temperatures and more humid conditions.
As you can see there is a lot to look into when putting together a winter forecast. There are still yet two more teleconnections we need to look at .. The next one is the Pacific Decadal Oscillation or PDO.

The Pacific Decadal Oscillation (PDO) is a pattern of Pacific climate variability similar to ENSO in character, but which varies over a much longer time scale. The PDO can remain in the same phase for 20 to 30 years, while ENSO cycles typically only last 6 to 18 months. The PDO, like ENSO, consists of a warm and cool phase which alters upper level atmospheric winds. Shifts in the PDO phase can have significant implications for global climate, affecting Pacific and Atlantic hurricane activity, droughts and flooding around the Pacific basin, the productivity of marine ecosystems, and global land temperature patterns. Experts also believe the PDO can intensify or diminish the impacts of ENSO according to its phase. If both ENSO and the PDO are in the same phase, it is believed that El Niño/La Nina impacts may be magnified. Conversely, if ENSO and the PDO are out of phase, it has been proposed that they may offset one another, preventing "true" ENSO impacts from occurring.


Warm PDO
The broad area of above average water temperatures off the coast of North America from Alaska to the equator is a classic feature of the warm phase of the Pacific Decadal Oscillation (PDO). The warm waters wrap in a horseshoe shape around a core of cooler-than-average water. Impacts from the PDO depend in part on how it is aligned with the ENSO cycle; if the cycles are in opposite phases, then effects will be weakened. However, when both the PDO and ENSO are in the warm phase, meaning ENSO would be in the El Niño phase, expected impacts on the southeast include:
Below average winter temperatures
Above average winter precipitation

Cold PDO
Opposite of the warm PDO, the expansive area of below average water temperatures off the coast of North America from Alaska to the equator signals the cold phase of the PDO. The area of warmer-than-average sea surface temperatures in the central Pacific are surrounded by below average temperatures near the North American continent. Expected impacts from a cold PDO and ENSO (La Nina) phase on the southeast include:
Above average winter temperatures
Below average winter precipitation
Where are we now with the PDO?

We are clearly in a negative phase with the Pacific Decadal Oscillation..
This leaves us yet to look at the QBO or the Quasi Biennial Oscillation.
The quasi-biennial oscillation (QBO) is a quasi-periodic oscillation of the equatorial zonal wind between easterlies and westerlies in the tropical stratosphere with a mean period of 28 to 29 months. The alternating wind regimes develop at the top of the lower stratosphere and propagate downwards at about 1 km (0.6 mi) per month until they are dissipated at the tropical tropopause. Downward motion of the easterlies is usually more irregular than that of the westerlies. The amplitude of the easterly phase is about twice as strong as that of the westerly phase. At the top of the vertical QBO domain, easterlies dominate, while at the bottom, westerlies are more likely to be found.
Effects of the QBO include mixing of stratospheric ozone by the secondary circulation caused by the QBO, modification of monsoon precipitation, and an influence on stratospheric circulation in northern hemisphere winter (the sudden stratospheric warming's).
Current QBO
-25.90 (click here)
So with what we are looking at right now we can say with certainty we know the following:
1. We are heading into a weak to moderate El Nino. There is nothing indicating that we are going to be heading into a strong El Nino.
2. With a present negative PDO ..this would indicate a warmer winter across the southeast region with less precipitation. Of course if the PDO were to go to a warm phase this would change that scenario and we are only in the month of July…
What we do not know at this point and time:
1. What the state of the NAO will be come winter 2012-2013.
2. What the state of the PNA will be come winter 2012-2013
3. What the state of the AO will be come 2012-2013.
These teleconnections are ultimately important for the outcome of winter. At the present time this is what the JAMSTEC seasonal model is showing for the December thru Feb time frame..

This closely resembles 2003 except the below normal temperatures are not as far west as 2003 was.
The purpose of this is to lay the foundation for the actual forecast once the teleconnections become more clear as to whether we will be dealing with a + NAO or a –NAO ..+ PNA or – PNA and + AO or – AO.
Perhaps one more thing to keep in mind is that when the Summer is hotter then normal.. a lot of times this can indicate a colder and snowier winter. A lot of variables to come into play this winter .
We will be updating this during the month of September when some of the teleconnections should be more clear

September 2012 Update...

Temperature Outlook for December to Feb 

Precipitation Outlook 

These two maps are what we think will entail the winter of 2012-2013. While it is to early to know what the AO & NAO & PNA will be like we looked back thru weather history to 1950 for El Ninos that followed at least a 2 year La Nina ...

First year we come across is 1957-1958 and that winter looked like this:

That winters precipitation...

The next El Nino that were to follow at least a 2 year La nina would be 1972-1973

And that precipitation was as follows:

Both 1957-1958 and 1972-1973 were strong El ninos...

The next year on the list would be 1976-1977 in which the temperature departures looked like this..

Precipitation for that year looked like this:

1976-1977 was a Weak La Nina ...

The final time that this has happened and as you can see it has not happened often at least since 1950 was 2002-2003..

And precipitation for the year was as follows:

It is obviously a small sample package that we have to work with this winter season but essentially what we have done is taken a blend of all the years above with more leaning on a blend of 1976-1977 and 2002-2003.. The first one being a weak El nino and the latter being a Moderate El nino. We think the winter of 2012-2013 should end up being between a weak and a moderate El Nino.