Hi it’s Rebecca again, this blog will be about my initial thinking on the upcoming Winter of 2012 – 2013. I've learned a lot from last years winter outlook. As I told you in last years outlook. I start to look at the indicators around this time of year. Although it is still summer, I start to to turn my attention to the upcoming winter season. This post will stay away from most of the meteorological mumbo jumbo ...but some of it is necessary....I will try to show you how to read and interpret the data for yourself.
Before I get started I want to mention the years I'm using as analogues.... that I am using to try and get a handle on this winter's potential. I used these years where a weak to moderate El Nino followed two La Nina's in a row.
It should be noted that while some of these years could be called neutral, I was looking to see if they were still in negative territory and it seemed that the two years in question remained connected by the same La Nina event, by one way or another. I want to point out, this is in no way a long range winter forecast. Most likely some things will change between now and December. Because I wanted to keep the length of this post under control; I didn’t go into a lot of detail on the different oscillation’s. So if you want more information here is Last years winter outlook. Before I get started I want to briefly talk about last winter.
Why the lack of snow and cold last winter? The largest problem for snow lovers last winter wasn’t only the La Nina, but rather the temperature of the stratosphere and the Madden Julian Oscillation (MJO). Most forecasters pay attention to the troposphere, but there are many variables that go into a long range outlook. So when I looked at the stratosphere, I observed that it is beginning to warm slowly as compared to last year when it reached record cold levels, promoting a very warm troposphere. I will talk about this oscillation in more detail later….but for now I want to say that the MJO plays a major role in jet stream placement. But most of us should remember last winter we had a jet that stayed to the north and that was very fast, this kept the pattern zonal. This along with a positive NAO that prevented arctic air from making big moves into the Northeast, and most of the U.S. for that matter. OK lets get into the data a bit.
What is the North Atlantic Oscillation (NAO) index...it's an index that measures the state of the Atlantic...it involves the differentiation of pressure between Iceland and Greenland down to the Azores and over into Spain. This is just one of oscillations that is important to our winter weather . The NAO helps to create blocking and helps to bring cold air into the northeast when in the negative phase...now it's been in the negative phase Since mid June thru now. The question is will this continue into the winter.
Now many long range weather prognosticators are saying because it's been in the negative phase for so long this will continue...However, I've been looking at the data..... and I say, not so fast. I'm going to turn this into a teaching moment.....I'm going to show my current thinking and why I'm disagreeing about which phase the NAO will be in.
When the NAO is positive the Atlantic is in a westerly phase. This would mean high pressure around the Azores....And low pressure around Iceland...This would mean the winds would be westerly. The more intense the index, the stronger the NAO, the stronger the westerly winds.... So of course, a negative NAO is when there's high pressure over the Iceland and low pressure down around Azores with easterly winds moving over the Atlantic.
The important thing I want you to get out of this is it's not the winds that are driving the NAO... it's the weather that's driving the NAO... and not the NAO that's driving the weather.
I've been asked , how do you forecast the NAO? I look at the sea surface temperature anomalies in May into June. The reason we use the sea surface temperature anomaly in May is that they tend to reoccur during the Winter based on my observations .
In May you're looking for a positive anomaly in the tropical Atlantic and a negative anomaly in the Mid Atlantic around the US East Coast. Then you will have another positive anomaly just south of Greenland and Iceland. This would mean a warm band of water in the tropics, cold band in the middle Atlantic, and a warm band from Newfoundland to south of Greenland and Iceland.
So if you see that setup in May it's normally a good indication you will see the same setup during the Winter....that would consequently mean the NAO would be negative and that would imply an area of blocking high pressure setting up around Greenland and low pressure setting up south of the blocking high. Ok let's take a look at how the Index looked for May 2012. what we look at is an average of cold water anomalies.
Here are three maps of the SST anomaly for May 2012
5/9/2012, what we see is an average of cold water anomalies around the tropical Atlantic. and an average of warm water anomalies south of Greenland. There are warm SST from Newfoundland over to Greenland .... However, There is hardly any real warming in the tropical Atlantic.
5/16/2012 ,We see cooler than normal waters through the tropical Atlantic with no real band of warm water band setting up. East of Newfoundland and the Northeastern seaboard the SST has increased a bit. ..but the bottom line is there is not a lot of warm water in the tropics.
5/30/2012, Again there is no sign of a warm water anomaly around the equator in the tropical Atlantic. and again warm off of Newfoundland. This is basically telling me that we are most likely to see a positive NAO for the winter of 2012-2013.
Now before you send your cards and letters.....let me say the way I read the NAO is a theory and is experimental....but it is based on observations and patterns that have occurred in the past. This is just where my thinking is at this time.....It more than likely will change to some degree, as we get closer to the end of October and November.
When making a winter long range outlook; there are other things I look at as well.........The sea ice extent and how it behaves during the Summer, How quickly the snow builds in Siberia, ENSO (La Nina or El Nino), and the PDO. There are other things as well, but those are the main ones.
El Nino is a warming along the dateline of the Pacific equatorial waters off of Peru over to Indonesia . And the area that must see warming to get a designated El Nino is the mid equatorial region. this area must stay warm for five cognitive monthly recorders. when that happens we get an official El Nino declared.
Here's the latest Sea Surface Temperature Anomaly map.
When you look at the NOAA SST anomaly chart there is significant warming from Peru into the mid equatorial region of the pacific. It's not an intense warming There is no darker orange or red showing up....so this is telling me during the winter of 2012 -2012 will see a weak to moderate El Nino.
As a side note....if you look at the SST above you will see the water is warm from Newfoundland over to Greenland....As I said above I look at sea ice ... The warming around Greenland as as caused a lot of blocking in the atmosphere more most of the Summer near Greenland. Because of this there has been an awful amount of ice melt in Greenland this Summer....This could have implications on the winter of 2012-2013...but it's too early to talk about that....I will return to this at the end of September into the first part of October.
Unisys SST chart again you see the warm water temps off of Peru and extending well into the central equatorial Pacific. You can also see the cool SST in the Gulf of Alaska heading down into the waters of the Pacific Northwest and the Central northern Pacific.....This is showing the PDO in a positive phase. When you see Positive PDO during an El Nino....The El Nino has a hard time keeping a foothold......this is why we're not seeing more warming along the dateline.....This is telling me there won't be a strong El Nino this coming winter.
When I looked at the SST in the Pacific for the 80's and 90's....the El Nino's during that time were very intense.....that was because the PDO is in a negative warm phase....this allowed the El Nino's to strengthen much easier.
It's sort of like trying to get hot water out of the kitchen faucet when you also have the cold water tap on...
SST anomaly from Jamstec IOD This shows the warm water stretching all the way from Peru almost to Indonesia. This model is forecasting a moderate El Nino...This also shows the cold water from the Gulf of Alaska and along the Northwest coast. You can see that this El Nino looks to be east based.
If you continue into Dec to Feb it shows the El Nino is better organized....this is normal because El Nino typically get's stronger around Christmas time. But you can see the water temperature is starting to cool off near Peru.
Now you can see the cooling is very evident out into the middle equatorial area.
Most of the ensembles are showing a weak to moderate El Nino. CFS v1 and CFS v2 show a long duration weak El Nino. When the SST is at 1 degree Celsius it’s showing a weak to borderline moderate...under 1 degree C is weak....over 1 to 1.5 degree C is moderate.... anything above 1.5 to 2 or 2.5 degree C is strong to very strong ....The CFS V2 is not showing anything getting into the strong category.
The atmosphere is still not into a El Nino state....it's still more or less still into a La Nina state...but that should chance in 6 to 8 weeks....but the bottom line is a weak to borderline moderate El Nino is very likely.
As I said, the PDO is going into a positive phase. (waters in the northern Pacific will be colder) There have been La Nina years that have been very lean ( as we saw last year).There have been El Nino years where we received a lot of snow. The reason for all this are variations is the PDO. Last year, we had a moderate to strong La Nina....however the PDO was negative.
When we have a negative PDO the storms coming into the Northeast don't have a lot of cold air to work with. With the PDO heading into positive territory...this should allow the cold to infiltrate farther south than it did last year. Therefore the East Coast and again the Northeast could see more cold air outbreaks than we saw for the winter of 2011-2012 (that wouldn’t be too hard considering how warm it was).
The Madden Julian Oscillation (MJO):
The Madden Julian Oscillation will be shunted into Octets 8-1. This is significant, because the MJO is a measure of pressures and temperatures over the Indian Ocean, which because of the amount of energy contained in that ocean control the global weather patterns..including jet stream patterns and SST’s. The MJO is one of many factors that contribute to the development of tropical cyclone The El Nino will become west based driving (Left- an example of a west-based El-Nino in 2003) the MJO into a favorable pattern for pushing the moisture stream into the west coast, and may result in the formation of more storms. This oscillation will also balance the core of warmth over Alaska and Siberia, as compared to last year when it was incredibly cold and snowy and the east coast was kept into a ridge of higher pressure.
Winters with weak-to-moderate cold, or La Nina, episodes or ENSO-neutral conditions are often characterized by enhanced 30–60 day MJO activity. A recent example is the winter of 1996–97, which featured heavy flooding in California and in the Pacific Northwest. The winter of 1996-1997 has become the bench mark that all other winters are judged against. That winter saw several Midwest and Northeast snowstorms including the Blizzard of 96 on January 6-8, 1996 and the March 31 - April 1 1997 Blizzard.
Given the aforementioned factors, This will translate into a ridge further west, mainly west of the Mississippi River, resulting in warmer than average temperatures, and below average precipitation, further worsening the drought situation. The far west coast, may have to deal with a consistent stream of weak to moderately strong storms which may dip further south. Depending on how cold it gets the Northeast could see more than a few storms. This also potentially gives the southeast a better shot of ice storms as the jet stream sags further south delivering a few major cold snaps.
Ok what does all of this mean?
Weak El Nino’s on average have a much greater effect on the east coast ..especially the Northeast. weak El Nino typically brings slightly below average temperatures to the country, while bringing more precipitation to the East Coast and below normal rainfall for the Southeast.
Normally during a El Nino the temperatures along the East Coast are below average Dec-Feb With this being said, I expect this Winter to not be like a typical El Nino, especially with regards to precipitation trends. This will largely be as a result of the cool phase of the PDO and the suppression of the subtropical jet further south. Snow in the eastern US would occur mostly from North Carolina north. With Ice in the more likely in parts of Texas, into the Tennessee valley and parts of the Southeast.
If the NAO does go positive we might not see much of a Greenland high. We wouldn’t see a pattern as zonal as we saw last year…but it would cut down on precipitation amounts. We would see a few Nor’easters; just not as many as we would see in a normal El Nino winter. However, if we see the NAO go negative then SE NYS and southern New England would end up seeing above average precipitation. This would include the Mid Atlantic.
But right now I think most of New York State and northern New England will see average to slightly above average precipitation, with southern New England and Southeast NYS seeing average to slightly below average precipitation. I think there is no doubt we will see more cold weather during winter 2012-2013. I’m not 100% sure how cold it might be. Right now, I feel we will see a slightly colder than average. I hope you notice I'm using the word precipitation and not snow......winter precipitation includes rain, snow, ice, and freezing rain.
I want to close with this. Most of the data I’ve seen is pointing toward the possibility of seeing a decent winter cold and snow wise…The analogs show that back to back La Nina’s followed by a Weak El-Nino saw very substantial winters 60% of the time. The only thing that’s keeping me from thinking that... is the fly in the soup...THE NAO...the NAO I saw in July. remember many times that pattern repeats again in December or January. However if the NAO does stay negative we could be in for a brutal winter. I will be back with an updated winter outlook in six to eight weeks……..BUT remember these were just my initial thoughts on the upcoming Winter of 2012 – 2013.
I hope you learned a thing or two…and most of all enjoyed reading this post…….I will be happy to answer any questions anyone has.
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