October Pattern Index! Predicting Winter AO from October, with 90+% accuracy?

[donsutherland1]

 http://www.americanwx.com/bb/index.php/topic/41639-seasonal-winter-20132014-forecast-based-on-opi-index/

Thank you.

[Typhoon Tip]

Why not perform this same statistical science for September and November ?  Temporally, is there a physical reason why October is special -- like, "Up, it's November 1, OPI no longer has any bearing,"  seems rather short sighted.   Some years, snow advance begins earlier, and there is also some stochastic variance intra-seasonally, where it may slow and speed up.  

 

It's impressive, sure, but it also seem very generic.  I think it's a great start, where a deeper spectral analysis should then take place.

 

Also, rightfully so, we see that this OPI has a similar trend-line as the AO going back a few decades.  We also note that the AO curve is passing into negative, and that combined with +SAI (part of the OPI root), not sure how that signals a +AO for this ensuing cold season.  

 

[skierinvermont]

Tip,

 

The SAI is indicating a moderately positive AO this winter.

 

The noveber stratosphere over Asia is also frigid, this is also a very strong correlation with a +AO winter.

 

All indicators point to a +AO winter.

[donsutherland1]

Why not perform this same statistical science for September and November ?  Temporally, is there a physical reason why October is special -- like, "Up, it's November 1, OPI no longer has any bearing,"  seems rather short sighted.   Some years, snow advance begins earlier, and there is also some stochastic variance intra-seasonally, where it may slow and speed up.  

 

It's impressive, sure, but it also seem very generic.  I think it's a great start, where a deeper spectral analysis should then take place.

 

Also, rightfully so, we see that this OPI has a similar trend-line as the AO going back a few decades.  We also note that the AO curve is passing into negative, and that combined with +SAI (part of the OPI root), not sure how that signals a +AO for this ensuing cold season.  

 

OPI_kiss.jpg

The OPI graph you referenced only goes through October 2012. The October 2013 value was around +1.6 (not shown on the chart). The +1.6 value would indicate a positive AO winter is ahead.

[HM]

Again, October is an important time of year and a fine temporal scale for AO predicting. Several things change around the globe from the old summer regime to the new winter regime during October. It is perfectly fine to use parameters during this month to see how fast or slow we are progressing toward winter. It is also ridiculous to think that the rate of change in snow cover during September will somehow affect the SAI to favor a more -AO. This myth has been debunked time and time again.

 

Finally, neither the SAI or OPI explain anything about decadal NAM variability, despite their correlations. Suddenly, you have new questions about why the OPI or SAI have trended a certain way overtime, now. The recent decadal spike in the AO during the 1980s-1990s has been explained with processes that make physical sense, such has halogen-killing ozone, volcanic activity etc.

[DTWXRISK]

 I have been following the OPI  thing for a  while.
 
their  work is   SERIOUS BS    because it has  fatal  flaw in the reasoning.

Tautology

 

Actually, the long-term r^2 value for OPI vs AO is around 0.83, which, while very strong signal, isn't a guarantee. Technically, 1 in 6 years have had a departure from the OPI's predicted value.

 

Granted, this isn't much comfort to winter lovers.

[DTWXRISK]

HM

 

Earlier this week a leading  weather energy forecasting  firm    issued a seasonal forecast which essentially said that there is little chance of a cold winter over North America and especially over the U.S.   And  they  made that analysis forecast based upon   a  piss poor   understanding of the SAI .

Their argument in a nutshell was that because there was early snowfall in late September before October 1...  The southward rate of increase in the Siberian snow cover  --  the  SAI --   was not impressive.

 Lets say that it is true  that   October 1 the snow cover was already as far south as it normally is on ,say , October 20 .. and therefore    the  snow did NOT expand  that   far south .

 What Judah Cohen found was a PROCESS  which exists between the rate of snow cover  buildup in Siberia   and how it impacts the phase of the AO.   It is the process  that is important here ...  NOT the fact that  the snow  fell on September 26 vs. October 2.
 
To suggest otherwise   is arguing that the process   has a  "magical start date "   of October 1  and ends of OCT 31.
 I do not see WHY   the snow  falling Siberia on one side of October 1   -- say  SEPT 26  is detrimental  to the  SAI  but if the same snow   falls   4 or  5  days later -Say OCT 2...   has a totally different and significant  implications for the SAI.
 

 

 

Again, October is an important time of year and a fine temporal scale for AO predicting. Several things change around the globe from the old summer regime to the new winter regime during October. It is perfectly fine to use parameters during this month to see how fast or slow we are progressing toward winter. It is also ridiculous to think that the rate of change in snow cover during September will somehow affect the SAI to favor a more -AO. This myth has been debunked time and time again.

 

Finally, neither the SAI or OPI explain anything about decadal NAM variability, despite their correlations. Suddenly, you have new questions about why the OPI or SAI have trended a certain way overtime, now. The recent decadal spike in the AO during the 1980s-1990s has been explained with processes that make physical sense, such has halogen-killing ozone, volcanic activity etc.

[DTWXRISK]

Sorry folks I aint impressed

  in this case   what   Ricardo  et al have done is  found an  extremely  warm winter  --- 2005-06    where the AO  was  strongly positive  all winter LONG and in OCTOBER . 

IN other words  warm winters  are warm because  they  are  warm winters. 
Golly... some   breakthrough .  

 Someone  get Dr Heidi Cullen on the phone.      

Are  these folks  ACTUALLY  saying  that the AO phase on OCT  NEVER  changes or flips in the Winter ? 
REALLY... and why would  any one   accept  that argument ?
 

 all they are doing is finding  winters with   strong +AO  and  finding  OCT with + AO...
then   are amazed at the connection.

 if you Look   for evidence for the Loch ness Monster  you  WILL find it. That doesnt  mean  Nessie is real.



 

 

 

 

 

Rip off of Cohens work:

Cohen says:

Step 1: October snow advance causes
Step 2: Perturbation in Siberia ie pattern change and
Step 3: Upward energy flux
Step 4: Disrupt PV
Step 5: Predict DJF AO/NAO 81% variability

Ricardo...
I am a genius I have discovered that at the end of October a Pertubation in Siberia causes a pattern change and upward energy flux that disturbs the PV and predicts 83% variability of DJF AO!

Ricardo demand the Nobel Prize lolololol!

 

I suggest you to read carfully this paragraph:

 

 

WINTER 2005-06

 

"In this new episode of the analyze another great winter season, very fruitful also in the Italian: we speak of the 2005-06 season.

We proceed in the usual way, or imagine we are at the end of October 2005 and will try to trace the projection winter forecast on the basis of the new technique that stems from the recent discovery.

We start from the OPI value at the end of October it closes sharply negative settling on the exact value of -0.73. However, as regards the axis of the vortex, this is extremely inclined (almost on the values ​​of the exceptional 1980-81 season already analyzed). Once again, therefore, it has to do with a very particular month of October, in virtue of the high degree of ellitticizzazione of VP despite it lies on an axis extremely tilted. Below the paper hemispheric 500 hPa geopotential anomalies relative to is highlighted in the axis of the VP axis (black)

 

 

 

 

 

As we see the axis (black line ), which is an output element of the software " Telemappa Next Generation" , it is very tilted and the two waves are obviously in position perpendicular to the axis itself. The latter are located in a very special and exactly :

- The wave 1 shifted much to the east (with respect to its natural peaceful ) and centered on the American continent ( the Hudson Bay area ) ;

- Wave 2 also shifted to the east and perfectly centered right on the Scandinavian Peninsula.

As we explained in our research , and as underlined in a previous appointment (analysis of 1980-81 season ) , when the axis is tilted so strongly , the level of intrusiveness of the waves is never over and the VP , even in situations of maximum planetary wave activity , maintains a certain level of "unity / unity " , never arriving to compete division (split ) .

Furthermore , always as anticipated in the episode dedicated to 1980-81 , in these situations in which the axis is very tilted , the SAI loses much ability to pattern playback Ottobrino significantly decreasing its predictive value sull'AO winter . This is because , despite the pattern Ottobrino is present very good ( rate ellitticizzazione high ) , because of an axis of the vortex strongly inclined lunges affect more the area peaceful / extreme Asia and Central Siberia keeps a field geopotential higher. In this regard for the season in analysis ( 2005-06 ), the SAI provided by a winter AO weakly positive while later there was a decidedly negative AO medium .

Ultimately, on the basis of these data inputs can be drawn the following conclusions for the winter season to come (2005-2006) :

- AO quarterly income totaled decidedly negative values ​​(range -0.5/-0.9 ) . In addition, in consideration of what was said above about the stability / compactness partial residual time of maximum wave action and by virtue of the development " chronological " the VP in October ( this very important topic will be treated well in the future) , it is exclude long periods of complete absence of wave activity ( "dead" periods ) and descents cold linked to planetary wave should occur at the level of time, fairly evenly , with greater preponderance in the middle phase of winter (on average, from late December to mid- February).

- With regard to the characteristics of any descents Arctic , this is clear from the scheme of the pattern perfectly Ottobrino ( see again figure on the previous pattern of October). In particular, as mentioned above, there is evidence of a wave Atlantic strongly centered on the Scandinavian Peninsula resulting in recurrence schema SCAND + , with frequent descents with the north- east .

 

Now , as we are not at the end of October 2005 but we are in 2013 then we see how it was the winter :

- Final value of the AO average of -0.81 and therefore close to the expected value of OPI .

- In addition , there has been countless runs cold distributed fairly evenly throughout the quarter and almost all characterized by a clear pattern SCAND + .

 Below is a long series of images ( downloadable from the archives meteociel cards NCEP ) in which it is clear once again a very strong correspondence between the pattern (pattern) of October and what has distinguished the best winter episodes ( episodes it is connected to maximum activity planetary wave ) , with evident recurrence PATTERN SCAND + .

 

 

also in this case any comment on the strong similarities / winter symmetries between the cards and that of October, would definitely compartment and superfluous .

 

In the future will present many more examples of the reanalysis forecast on forecasts made ​​on the basis of this new " technology forecasting ." However, after these first four episodes , emerges very clearly the extraordinary nature of this new approach in terms of improving forecasting capabilities upon forecsast winter season .Is in fact evident as well , in addition to having a highly reliable information on the exact value of the average compactness of VP winter ( milestone unthinkable a short time ago) , it risecano to obtain with ease information relating to the dominant pattern during the winter season already in October , which was not possible (at least with this level of detail ) using the traditional predictive tools (from which we could only get maximum information ) . In addition, combining the final value of OPI to other important considerations that will make public in the next few days, you can get incredibly truthful information about the chronological development of the dynamics winter . And the ease of use of this technique will make it accessible to everyone ( even the less experienced ) the "world of teleconnections " and seasonal forecasts . And of course everything is based on what is most important to the scientific world , or the demonstration of a strong correlation between the VP in its first stage of development and the VP in the same phase of maximum expression and maturity ( this factor may open an important horizon for institutions to calculate the development of more accurate models to forecast seasonal ) .

Finally, we anticipate even now that in the future we will have the ability to implement more about our software applications that allow us to achieve a level of detail and precision even wider ".

 

 

 

In this page you can read the other analysis:

 

http://www.centrometeotoscana.it/forum/index.php?topic=7371.0

 

So in these you can feel the differences between our work and Coehn Work. First our correlation is very most strong; second our work has more consequences both for the actually prediction abilyties and for the future scentific researh development (to understand that the correlation is internal to the polar vortex and that the snow-cover-winter AO is "only" a derivative correlation, rapresent a very important step to improve the forecast model). So our work is a "natural" important  development of Cohen work (as said into the our research).

To conclude I rember you that other authors and I are simple amaterus that have worked only six months in this research (of course during the little free time because of the "real life obbligations"). Instead Cohen is a very important researcher that has been worked about "snow cover phenomena" since 1990.

 

Goodbye

 

 

Riccardo

 

 

 

 

 

 

 

 

[DTWXRISK]

.........To conclude it is important to remark that there is a STRONG correspondence between the october pattern (when the NEW winter VP is being born) and the winter pattern (when the VP ITSELF is "adult") and that the correlation between snow cover-winter AO is only a derivative correlation. I think that this discovery can be useful in order to improve the GCM (climatic global model)..................

 

 

um what if OCT  pattern  is not the  real winter pattern?

[donsutherland1]

Sorry folks I aint impressed

  in this case   what   Ricardo  et al have done is  found an  extremely  warm winter  --- 2005-06    where the AO  was  strongly positive  all winter LONG and in OCTOBER . 

IN other words  warm winters  are warm because  they  are  warm winters. 

Golly... some   breakthrough .  

 Someone  get Dr Heidi Cullen on the phone.      

Are  these folks  ACTUALLY  saying  that the AO phase on OCT  NEVER  changes or flips in the Winter ? 

REALLY... and why would  any one   accept  that argument ?

 

 all they are doing is finding  winters with   strong +AO  and  finding  OCT with + AO...

then   are amazed at the connection.

 if you Look   for evidence for the Loch ness Monster  you  WILL find it. That doesnt  mean  Nessie is real.

 

Dave,

 

Hopefully, the paper will be published soon, so we'll know more about the details involved. The coefficient of correlation seems promising and it will be useful to see how things fare in a forecasting situation. Certainly, I hope that their work stands up, as anything that reduces the degree of uncertainty in seasonal forecasting would be a welcome development.

 

I agree with you that the October AO phase does not assure the predominant winter phase, though a strongly negative October AO (-0.5 or below for the monthly average) has a high rate of a December-February AO-. The same does not hold with strongly postive October AO figures (+0.5 or above). FWIW, below are the 1950-2012 statistics:

 

October AO:

-0.5 or below: 13/16  (81%) winters had a negative average

Above -0.5 and below +0.5: 19/31 (61%) winters had a negative average

+0.5 or above: 8/16 (50%) winters had a negative average

 

1950-2012: 40/63 (63%) winters had a negative average

[Mallow]

HM

 

Earlier this week a leading  weather energy forecasting  firm    issued a seasonal forecast which essentially said that there is little chance of a cold winter over North America and especially over the U.S.   And  they  made that analysis forecast based upon   a  piss poor   understanding of the SAI .

Their argument in a nutshell was that because there was early snowfall in late September before October 1...  The southward rate of increase in the Siberian snow cover  --  the  SAI --   was not impressive.

 Lets say that it is true  that   October 1 the snow cover was already as far south as it normally is on ,say , October 20 .. and therefore    the  snow did NOT expand  that   far south .

 What Judah Cohen found was a PROCESS  which exists between the rate of snow cover  buildup in Siberia   and how it impacts the phase of the AO.   It is the process  that is important here ...  NOT the fact that  the snow  fell on September 26 vs. October 2.

 

To suggest otherwise   is arguing that the process   has a  "magical start date "   of October 1  and ends of OCT 31.

 I do not see WHY   the snow  falling Siberia on one side of October 1   -- say  SEPT 26  is detrimental  to the  SAI  but if the same snow   falls   4 or  5  days later -Say OCT 2...   has a totally different and significant  implications for the SAI.

 

 

Which is all fine and dandy, except that it has already been noted several times that even if you shift the start date back four days and calculate the "SAI" based on that, it still strongly supports a +AO winter. This is (partly) because the SAI is calculated as a regression line through all 31 days, so it's not strongly sensitive to shifting the window around by a few days.

 

On top of that, you mention that Cohen suggests a process (a five-step process, to be precise). Indeed he does, and so far the atmosphere has been responding as expected to the October SAI. In other words, the signs we are seeing so far through November continue to strongly point to a +AO winter. And lest you misread that, a +AO winter does not mean the AO must be positive the entire winter--nobody here has ever suggested that.

 

If you want to latch on to something that supports your argument, it can't be the SAI. Instead, you could use Cohen's earlier work, the average Eurasian snow cover extent (SCE) during October. That was a little above normal this October, which would weakly support a -AO winter. Just be careful in doing so, since the correlation between that index and winter AO is much less convincing than the correlation between the SAI and the winter AO. And with the fact that things so far in November are supporting the SAI over the SCE, I'd be even more cautious about latching onto the SCE.

 

 

 

EDIT: Also, re: your last paragraph, statistically speaking, snow falling on October 2nd (or even October 8th) is detrimental to the SAI. There is no great change on October 1st where snowfall goes from being detrimental to the SAI to it being a boon. Since a regression line is fit through the days, the "best case scenario" is for generally low snow early on (say in the first half of the timeseries) and then high snow later (in the second half). That's why shifting the start date this year doesn't actually improve the SAI number.

[skierinvermont]

DT,

 

The SAI is very positive no matter when you pick the start date.

 

Pick any start date you want. The SAI is POSITIVE.

 

Plus, the correlation IS strongest with an OCT 1 start DATE.

[skierinvermont]

Nov 1 thru 16 has had a very cold Asian stratosphere. This has a strong correlation with a +AO winter.

 

 

 

[tacoman25]

Nov 1 thru 16 has had a very cold Asian stratosphere. This has a strong correlation with a +AO winter.

 

Nov 1 to 16.gif

 

Looks like the biggest anomalies by far are over the Aleutians. Any known significance to that?

[skierinvermont]

Looks like the biggest anomalies by far are over the Aleutians. Any known significance to that?

 

Cold aleutians still correlates to a +ao but it's on the edge. Strongest correlation is over east asia, where it is also cold. I wouldn't try to read too much into the details. When the November Asian stratosphere is this cold, the DJ AO is almost always ++AO

[toronto blizzard]

Cold aleutians still correlates to a -ao but it's on the edge. Strongest correlation is over east asia.

So then maybe the AO won't be too positive.

[Mallow]

So then maybe the AO won't be too positive.

 

Skier meant +AO, as you can see in his map (negative correlation means cold => +AO).

[skierinvermont]

yes, fixed.

[Jonger]

While we trade ideas back and forth on this, the long range models look excellent for cold.... I'm liking what I'm seeing on the upcoming period.

Major Lake effect outbreak coming this weekend possibly, brief moderation and then a real solid trough.

[Ginx snewx]

yes, fixed.

I believe your theory was debunked last year.

[skierinvermont]

I believe your theory was debunked last year.

 

You are mistaken. 

 

First of all, it isn't a theory it is an observed mathematical correlation with a large sample size which is not 'debunked' by one year. The December AO is 1.09 higher and the January AO 1.79 higher following a 'cold' November Asian stratosphere than a 'warm' one. Years where it remains negative the entire month have an even stronger correlation. If the asian stratosphere is cold at the end of November, it basically guarantees a -AO because it takes time for SSW to propagate. I didn't break it down into this level of detail.

 

Second of all, the method correctly predicted a -AO last winter. For much of November the signal was mixed, but if you break November down by week, you see the second half of November had a warm asian stratosphere, which indicated a -AO winter. The last week of November had a large warming event which indicated a very -AO winter. 

 

Third, I never predicted a +AO winter. I spent much of November saying the signal was mixed and we needed to wait until the end of November. On November 24th I said that if the late November SSW event came to fruition, we would have a -AO winter:

 

 

Complete stratospheric vortex split by D7 look at the massive warm anomalies at 70mb over Asia. If anything like this comes to fruition, it bodes extremely well for the first two months of winter.

 

 

 

The split came to fruition and we had a -AO winter. 

 

In 2012 this method correctly predicted the sign of the DJ AO by November 24th (possibly earlier if you believed stratosphere forecasts from Nov 19th onward).

 

Checking my posts from 2011, In 2011 this method correctly predicted the sign of the DJ AO by November 17th. 

 

So as a predictive method the past two years, the method is 2/2. If the PV is intact by the end of November you will have a +AO DJ (2011-2012). If it is disrupted by the the end of November you will have a -AO DJ (2012-2013). 

 

 

For 2013, I am not ready to declare a +AO based on asian stratosphere temperatures (although it is looking that way). Time remains for an SSW to save us. But SAI and OPI are both indicating a +AO. While their lead time is longer, the correlation is not as great. If the PV remains intact 2 weeks from now, we can be more certain of a +AO winter.

[Jonger]

The AO might be postive, but its not the death knell on winter....

 

Last December, which sucked, was running an AO of -3.50 around the time the eastern US was torching.

 

The pacific will dictate your winter more than the AO.

 

The AO is somewhat over-rated north of 40.

[tacoman25]

The AO might be postive, but its not the death knell on winter....

 

Last December, which sucked, was running an AO of -3.50 around the time the eastern US was torching.

 

The pacific will dictate your winter more than the AO.

 

The AO is somewhat over-rated north of 40.

 

This is what I've been trying to tell people. So much emphasis on the AO, and while it certainly is a major factor for winter (especially further south as you said), EPO blocking often has more direct correlations for the CONUS temperatures.

[Jonger]

This is what I've been trying to tell people. So much emphasis on the AO, and while it certainly is a major factor for winter (especially further south as you said), EPO blocking often has more direct correlations for the CONUS temperatures.

 

The AO being positive, definitely loads the dice in favor of a warmer winter, but the Pacific is the real factor that can override any AO index.

[donsutherland1]

This is what I've been trying to tell people. So much emphasis on the AO, and while it certainly is a major factor for winter (especially further south as you said), EPO blocking often has more direct correlations for the CONUS temperatures.

AO is one big piece to the puzzle, but most definitely not the only one. Sometimes extreme AO situations can overwhelm other variables. But the Pacific is also important. An extreme EPO can also dominate the pattern.

 

Finally, it should be noted that as one goes north, blocking can lead to warmer outcomes, not colder ones, as the anomalously cold air is driven southward.

[easternsnowman]

A negative AO will help those NYC south,look at some recent winters where they got colder more snowier years than us further north , then look at 2007-2008 where  those N of NYC got big snows while south of 40 had single digit snowfall totals!

[tacoman25]

A negative AO will help those NYC south,look at some recent winters where they got colder more snowier years than us further north , then look at 2007-2008 where  those N of NYC got big snows while south of 40 had single digit snowfall totals!

 

Yup, but then there was also 2010-11...which despite a massive -AO at times still favored those further north (at least along the East Coast). Last winter turned markedly colder for the CONUS overall after mid January when a sustained -EPO period set in. 2007-08 was a winter with very little -EPO. In addition, many of the coldest periods of 2008-09, 2009-10 and 2010-11 happened during -EPO. The cold in the eastern US this month is -EPO driven (despite a raging +AO).

 

There are many winters where CONUS cold is much more closely correlated to the EPO than the AO.

[HM]

HM

 

Earlier this week a leading  weather energy forecasting  firm    issued a seasonal forecast which essentially said that there is little chance of a cold winter over North America and especially over the U.S.   And  they  made that analysis forecast based upon   a  piss poor   understanding of the SAI .

Their argument in a nutshell was that because there was early snowfall in late September before October 1...  The southward rate of increase in the Siberian snow cover  --  the  SAI --   was not impressive.

 Lets say that it is true  that   October 1 the snow cover was already as far south as it normally is on ,say , October 20 .. and therefore    the  snow did NOT expand  that   far south .

 What Judah Cohen found was a PROCESS  which exists between the rate of snow cover  buildup in Siberia   and how it impacts the phase of the AO.   It is the process  that is important here ...  NOT the fact that  the snow  fell on September 26 vs. October 2.

 

To suggest otherwise   is arguing that the process   has a  "magical start date "   of October 1  and ends of OCT 31.

 I do not see WHY   the snow  falling Siberia on one side of October 1   -- say  SEPT 26  is detrimental  to the  SAI  but if the same snow   falls   4 or  5  days later -Say OCT 2...   has a totally different and significant  implications for the SAI.

 

 

I think your issue is with the forecasting firm not the research. But it is also clear that you unfairly criticized the research, too, as others have pointed out.

 

If your problem is that people are suggesting a warm winter based solely on the SAI...fine (I think any sensible forecaster would agree that it's not too bright to base a temperature forecast on 1 variable)... but if you actually think the SAI suggests a -AO this year, you are seriously misreading the variable.

 

Here's the facts on the actual, physical processes right now: there aren't too many autumns as suggestive as 2013 for a +AO. Even if you take away the OPI and SAI, the wave/jet behavior is classic leading to a +NAM. The anomalous PV-cyclonic streamfunction over Siberia with poleward anticyclones are ugly for -AO predictions. The SAI / OPI just elucidate these observations. While there have been wave disturbances, none of these can be traced back to the actual snow cover, especially that of the late September period since the vortex is still forming!

 

The vortex really comes on in October and peaks in January, strength-wise. Upwelling waves in early autumn are basically useless in affecting the NAM state.

[HM]

Here is the current poleward eddy heat flux at 100mb:

Despite the "early start" with wave genesis, the flux has been average to below average. As we have gotten closer and closer to winter and the PV has gotten stronger and stronger, the waves have had less and less impact. Womp...

In 2009, on the other hand, it looked pretty good at this point (and remember, November 2009 was pretty warm):

[DTWXRISK]

 SORRY  SKI   and HM  but  JUDAH  COHEN says I am right ...sort of  

you know the   guy who developed and  found the  SAI / AO connection 
 

http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/11/20/judah-cohens-winter-outlook-a-downer-for-east-coast-winter-weather-lovers/

 

But there’s one wrinkle this year, Cohen says. Even though Siberian snow advanced much more slowly than normal this October, its overall extent was substantially above normal. Such a mixed signal makes this year’s AO forecast more uncertain, Cohen stresses.

 

QUOTE FROM  COHEN
 

 This October was highly anomalous in that the snow cover extent [sCE] and the snow advance index [sAI] strongly diverged. The SCE was well above normal, which is a robust prediction of a negative winter AO while the SAI was well below normal, which is a robust prediction of a positive winter AO. This has never happened over the forty years that we have calculated both indices. I view the SAI as the more reliable predictor but I also think it would be a mistake to dismiss the high Siberian SCE from this past October. How the two predictions evolve this winter should be interesting.