Winter 2014-2015 Thread

[clskinsfan]

It's a joke, designed to be a joke.  

 

Ah. Makes sense now. Figured it had to be with all of the bread and milk stuff.

[wildweatherman179]

I'll take an order of #2, #9 and #10 with a side order of #13. Lol

[EastCoast NPZ]

It's a joke, designed to be a joke.  

 

I know, which is why I said it's good for a laugh.  The headline ticker stories at the top of the page (Poltergeist possession of microwave, and KKK wizard using membership card for grocery store discounts) kind of gave it away.  LOL.

[mattie g]

Earliest snow on record for Rapid City SD

https://twitter.com/NWSRapidCity/status/510083127213973504

Of course, it was only a matter of tweets before some douchebag made a comment on global warming/climate change.

[StudentOfClimatology]

I like a blend of 1951-52/1958-59/1968-69/1979-80 this winter. Stratospheric analogs I'm using suggest a warm

Sep-Oct-Nov overall, questionable progression into Nov/Dec, but are all clear on a major SSW/subsequent drop in the AO come late Dec or Jan.

January could be the month this year. Very worthwhile data on the stratosphere here: http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/northpole/index.html

C= Major Mid-Winter warming/SSW

CW= Canadian Warming (rare nowadays)

FW= Final Warming

TRT= Transition time to summer PV state from winter PV state. Well correlated to Mar/Apr NAM/temps

[GaWx]

I like a blend of 1951-52/1958-59/1968-69/1979-80 this winter. Stratospheric analogs I'm using suggest a warm

Sep-Oct-Nov overall, questionable progression into Nov/Dec, but are all clear on a major SSW/subsequent drop in the AO come late Dec or Jan.

January could be the month this year. Very worthwhile data on the stratosphere here: http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/northpole/index.html

C= Major Mid-Winter warming/SSW

CW= Canadian Warming (rare nowadays)

FW= Final Warming

TRT= Transition time to summer PV state from winter PV state. Well correlated to Mar/Apr NAM/temps

 

SoC,

 I honestly think 1951-2 and 1968-9 shouldn't be considered because of their strong -PDO during winter. I feel that a +PDO is quite likely for this winter averaged over DJF.

[StudentOfClimatology]

SoC,

I honestly think 1951-2 and 1968-9 shouldn't be considered because of their strong -PDO during winter. I feel that a +PDO is quite likely for this winter averaged over DJF.

Possibly, but I'm personally skeptical. Though I agree the pattern over lower-48 shouldn't resemble 1951-52 at all. I'm mostly using these analogs to determine the progression in the NAM/AO.

My research suggests the PDO is, for the most part, overrated. The SSTs over the NPAC lag the atmospheric circulation there by several months, and ENSO/tropical forcings seem to govern the entire PDO dynamic.

Static thermodynamics suggests you'd generally get additional lift over warm SSTs, visa versa over colder SSTs...not the other way around. The tropical forcings that govern the NPAC circulations seem to govern the PDO, rather than a pseudo-reverse coupling of sorts.

The 1960s & 1990s winter illustrate this case very well. The 1989-1995 era was loaded with +PDOs/Niños, yet we know how that turned out. Same goes for the late 1950s/1960s winters. What you're seeing are ENSO/QBO/Ozone/Solar forcings.

[GaWx]

Possibly, but I'm personally skeptical. Though I agree the pattern over lower-48 shouldn't resemble 1951-52 at all. I'm mostly using these analogs to determine the progression in the NAM/AO.

My research suggests the PDO is, for the most part, overrated. The SSTs over the NPAC lag the atmospheric circulation there by several months, and ENSO/tropical forcings seem to govern the entire PDO dynamic.

Static thermodynamics suggests you'd generally get additional lift over warm SSTs, visa versa over colder SSTs...not the other way around. The tropical forcings that govern the NPAC circulations seem to govern the PDO, rather than a pseudo-reverse coupling of sorts.

The 1960s & 1990s winter illustrate this case very well. The 1989-1995 era was loaded with +PDOs/Niños, yet we know how that turned out. Same goes for the late 1950s/1960s winters. What you're seeing are ENSO/QBO/Ozone/Solar forcings.

1) Very interesting. I've often wondered & occasionally mentioned the possibility of somewhat of a chicken-egg aspect of PDO. However, if the PDO SST pattern were to go deep down enough into the subsfc, then I could see PDO being more of the driving force & not other way around.

2) I've gotten the impression that PDO Regime (not phase) & Enso phase sort of influence each other. I've noticed more strong Ninos during +PDO regimes for one & more weak Ninos/Nina in general w/-PDO.

3) I see strong correlation between +PDO & colder E US winter when Niño weak as well as some other ENSO.

[StudentOfClimatology]

Nice post.

I think the chicken-egg thing tricks a lot of people, myself included for awhile. Just like ENSO, the PDO SST signature is governed by wind-driven upwelling/downwelling. A cold PDO is generally associated with a deeper -AAM like circulation originating in the tropics (Walker Cell/MJO) and long term trends in the PDO can be attributed/correlated to long term shifts in global circulation...not just NPAC circulation.

On shorter timescales, I think tracking every blip in the PDO is silly, because you're really just looking at what's already happened, IE: the atmosphere's influence on those SSTs.

[AvantHiatus]

Nice post.

I think the chicken-egg thing tricks a lot of people, myself included for awhile. Just like ENSO, the PDO SST signature is governed by wind-driven upwelling/downwelling. A cold PDO is generally associated with a deeper -AAM like circulation originating in the tropics (Walker Cell/MJO) and long term trends in the PDO can be attributed/correlated to long term shifts in global circulation...not just NPAC circulation.

On shorter timescales, I think tracking every blip in the PDO is silly, because you're really just looking at what's already happened, IE: the atmosphere's influence on those SSTs.

SSTs feed back on themselves, hence why the Eastern US has been constantly overun with cool airmasses this summer/spring. Despite this, many areas have averaged slightly warm. I don't really have any high hopes for this winter to be honest. It will largely depend on the NAO and Canadian snowcover.

[StudentOfClimatology]

SSTs feed back on themselves, hence why the Eastern US has been constantly overun with cool airmasses this summer/spring. Despite this, many areas have averaged slightly warm. I don't really have any high hopes for this winter to be honest. It will largely depend on the NAO and Canadian snowcover.

In a static thermodynamic model, you get additional lift/evaporation/convection over warmer SSTs and sinking air over cold SSTs (lower surface pressures over warm SSTs, higher surface pressures cold SSTs).

There is no feedback mechanism that would force ridging over warm SSTs, and visa versa over cold SSTs. The reason we see this occur is because the ridging is forcing the warm SSTs...troughing/winds/clouds force the negative SSTs.

In the tropics, you see this occur constantly w/ the MJO biased towards the warmer SSTs/influenced by ENSO. Why would this relationship magically reverse over the NH?

The mid latitude circulations are governed by the heat-loaded tropical forcings, and other aspects too like the QBO/solar forcing on the PV/AO.

[Bob Chill]

Nice post.

I think the chicken-egg thing tricks a lot of people, myself included for awhile. Just like ENSO, the PDO SST signature is governed by wind-driven upwelling/downwelling. A cold PDO is generally associated with a deeper -AAM like circulation originating in the tropics (Walker Cell/MJO) and long term trends in the PDO can be attributed/correlated to long term shifts in global circulation...not just NPAC circulation.

On shorter timescales, I think tracking every blip in the PDO is silly, because you're really just looking at what's already happened, IE: the atmosphere's influence on those SSTs.

True, but I'm mostly interested in the multi-month decline and whether it continues to fall or rebounds. Being in an overall -pdo period makes the anomalous +pdo periods important to watch for. Especially considering the string of dogs we had post 09-10. Last year was the first time the pdo flipped + after 3 straight ghastly years following 09-10.

I don't focus on the PDO with temps much at all. That can easily be overcome with a favorable ao/nao. But it definitely affects precip patterns and storm track. The short version is miller A's are much less common during -pdo winters than + ones. If we end up with a -pdo on the means this coming winter I we'll likely end up with cutters, runners, clippers, and jumpers. Congrats NE.

[Bob Chill]

I just went back and looked at DCA's top 10 snowstorms. 9 out of 10 were during +PDO months. The only outlier was Feb 1979. 78-79 was a nino hangover year and featured lots of blocking to keep our area cold. I'm much rather rely on a favorable Pac vs crappy Pac and pray the Atl cooperates.

[StudentOfClimatology]

True, but I'm mostly interested in the multi-month decline and whether it continues to fall or rebounds. Being in an overall -pdo period makes the anomalous +pdo periods important to watch for. Especially considering the string of dogs we had post 09-10. Last year was the first time the pdo flipped + after 3 straight ghastly years following 09-10.

I don't focus on the PDO with temps much at all. That can easily be overcome with a favorable ao/nao. But it definitely affects precip patterns and storm track. The short version is miller A's are much less common during -pdo winters than + ones. If we end up with a -pdo on the means this coming winter I we'll likely end up with cutters, runners, clippers, and jumpers. Congrats NE.

Thanks for the reply.

I totally agree with the correlations you've observed, I see them too. I just don't think the NPAC SSTs are the forcing mechanism...rather the circulations/tropical forcings responsible for the SST shifts seem to be the culprit behind the wave train differentials as well.

I remember when that big SSW/-AO occurred in January 2013, we had that big MJO wave erupt in response to the cooling of the tropical stratosphere that resulted. That MJO wave battled with the Niña-esque Walker Cell for awhile, but eventually won out, and forced that big -EPO ridge that I thought would never return.

Turns out that January 2013 event sparked a major shift, as ridging/warm SSTs have dominated the NPAC since then, and can be attributed to the new tropical forcing regime that has dominated since then.

[GaWx]

I just went back and looked at DCA's top 10 snowstorms. 9 out of 10 were during +PDO months. The only outlier was Feb 1979. 78-79 was a nino hangover year and featured lots of blocking to keep our area cold. I'm much rather rely on a favorable Pac vs crappy Pac and pray the Atl cooperates.

 

For the several dozen major ATL S/IP, the average PDO was ~+0.50. So, there has, indeed, been a partial correlation of major ATL S/IP with +PDO though not a strong correlation. Note, however, I said correlation rather than causation. I can't prove that the higher PDO, itself, actually causes increased S/IP tendencies even though it is quite possible. In deference to what SoC said, it may just be that the world atmospheric conditions that lead to +PDO's also tend to increase ATL S/IP. The correlation to -NAO has been stronger since avg. NAO was nearly down to -1. I suspect that the -NAO/major ATL S includes some sort of indirect causation element and not just correlation.

[millwx]

1) Very interesting. I've often wondered & occasionally mentioned the possibility of somewhat of a chicken-egg aspect of PDO. However, if the PDO SST pattern were to go deep down enough into the subsfc, then I could see PDO being more of the driving force & not other way around.

2) I've gotten the impression that PDO Regime (not phase) & Enso phase sort of influence each other. I've noticed more strong Ninos during +PDO regimes for one & more weak Ninos/Nina in general w/-PDO.

3) I see strong correlation between +PDO & colder E US winter when Niño weak as well as some other ENSO.

GaWx,

 

Haven't posted on here in a long time (years!), but I've been lurking.  Given my fairly extensive research on this, I feel compelled to post...

 

1)  I'd disagree somewhat with SofC on his assertion that the PDO is a result, not a cause.  To be clear, I'm NOT trying to throw him under the bus.  He is absolutely correct, on some level (see his comments further downthread); and, in fact, it why the ridging does not set up directly overhead of the warm SST pool.  Furthermore, one of the beauties of meteorology is that it is still evolving... we are still studying and trying to understand things.  Also, from a mechanical wind forcing mechanism, just as it is trade wind anomalies which are largely the culprit in ENSO forcing, some studies have also shown the PDO resulting from wind forcing.  To that end, it IS the result of a pattern.  BUT... the suggestion (and I know that SofC did not say this directly... again, I'm NOT really trying to contradict him... just trying to offer an alternative angle) that the PDO does not, in turn, influence North American weather - that it is merely the result of the already established pattern makes little physical sense AND is not supported by the statistics.  Why it makes no physical sense is that the water has a much higher heat capacity, DOES interact with the atmosphere (which is why the newer, better models are ocean-atmosphere coupled), and is upstream from North America.  It is completely implausible that the PDO would yield zero influence on U.S. weather.  Furthermore, it is not supported by the data.  The highest correlation between PDO and U.S. weather is winter to winter, which is, in fact, meaningless to my point... proves nothing.  BUT, autumn PDO to U.S. winter also has a relatively high correlation.  And, in fact, further upstream... NW Pacific SST anomalies to U.S. winter correlation peaks in autumn, not winter.  So, from a purely statistical standpoint - approaching it blindly, with no knowledge of physical processes - the PDO leads U.S. weather - does not lag it - which, implicitly, would indicate a causal relationship.  And I'll say it again... NOT really/entirely disagreeing with SofC - he raises some excellent, valid, correct points.  I am merely stating that, even if the PDO is the result of the pattern, it does at least, in turn, have some feedback onto the pattern.  This is both logical (even SofC implies as much in his downthread post when he points out how the warmer SSTs have atmospheric influences) and supported by the statistics.

 

2)  To your PDO/ENSO relationship point... you are absolutely correct.  This has actually been studied before.  There is a positive correlation between PDO and ENSO.  It is absolutely no coincidence that ever since we entered a the negative PDO cycle that La Ninas have dominated over El Ninos.  It is also no coincidence that the reverse was true when we were in a positive PDO cycle prior to that.  In turn, it should not shock anyone that, despite being in a negative PDO AND La Nina-dominated phase, we appear to be set up to achieve BOTH a positive PDO *and* El Nino in the same winter.  Mind you, the correlation is FAR from 100% of course.  It's easy to get opposing signals at any given time.  But, as a general rule, there is a positive correlation.

 

FYI, some background on me since I've not posted here in so long... I'm a met in the energy field (and contrary to the implications - I think in the New England thread - we did not ALL miss last winter, hehe ;-) ...and if you're wondering about my own thinking for this winter... A) it's a little early; still waiting for some things to be settled; as a good energy met, I don't leak my forecast in public forums, hehehe; C) but I will just tell you that my PRELIMINARY assessment is in general concurrence with what seems to be the most common expectation for the winter - you can probably successfully read between the lines there).  Been in that sector for about 10 years.  Prior to that I was doing research met for almost 15 years.  Damn, I'm getting old.  Lol.

[StudentOfClimatology]

GaWx,

Haven't posted on here in a long time (years!), but I've been lurking. Given my fairly extensive research on this, I feel compelled to post...

1) I'd disagree somewhat with SofC on his assertion that the PDO is a result, not a cause. To be clear, I'm NOT trying to throw him under the bus. He is absolutely correct, on some level (see his comments further downthread); and, in fact, it why the ridging does not set up directly overhead of the warm SST pool. Furthermore, one of the beauties of meteorology is that it is still evolving... we are still studying and trying to understand things. Also, from a mechanical wind forcing mechanism, just as it is trade wind anomalies which are largely the culprit in ENSO forcing, some studies have also shown the PDO resulting from wind forcing. To that end, it IS the result of a pattern. BUT... the suggestion (and I know that SofC did not say this directly... again, I'm NOT really trying to contradict him... just trying to offer an alternative angle) that the PDO does not, in turn, influence North American weather - that it is merely the result of the already established pattern makes little physical sense AND is not supported by the statistics. Why it makes no physical sense is that the water has a much higher heat capacity, DOES interact with the atmosphere (which is why the newer, better models are ocean-atmosphere coupled), and is upstream from North America. It is completely implausible that the PDO would yield zero influence on U.S. weather. Furthermore, it is not supported by the data. The highest correlation between PDO and U.S. weather is winter to winter, which is, in fact, meaningless to my point... proves nothing. BUT, autumn PDO to U.S. winter also has a relatively high correlation. And, in fact, further upstream... NW Pacific SST anomalies to U.S. winter correlation peaks in autumn, not winter. So, from a purely statistical standpoint - approaching it blindly, with no knowledge of physical processes - the PDO leads U.S. weather - does not lag it - which, implicitly, would indicate a causal relationship. And I'll say it again... NOT really/entirely disagreeing with SofC - he raises some excellent, valid, correct points. I am merely stating that, even if the PDO is the result of the pattern, it does at least, in turn, have some feedback onto the pattern. This is both logical (even SofC implies as much in his downthread post when he points out how the warmer SSTs have atmospheric influences) and supported by the statistics.

2) To your PDO/ENSO relationship point... you are absolutely correct. This has actually been studied before. There is a positive correlation between PDO and ENSO. It is absolutely no coincidence that ever since we entered a the negative PDO cycle that La Ninas have dominated over El Ninos. It is also no coincidence that the reverse was true when we were in a positive PDO cycle prior to that. In turn, it should not shock anyone that, despite being in a negative PDO AND La Nina-dominated phase, we appear to be set up to achieve BOTH a positive PDO *and* El Nino in the same winter. Mind you, the correlation is FAR from 100% of course. It's easy to get opposing signals at any given time. But, as a general rule, there is a positive correlation.

FYI, some background on me since I've not posted here in so long... I'm a met in the energy field (and contrary to the implications - I think in the New England thread - we did not ALL miss last winter, hehe ;-) ...and if you're wondering about my own thinking for this winter... A) it's a little early; still waiting for some things to be settled; as a good energy met, I don't leak my forecast in public forums, hehehe; C) but I will just tell you that my PRELIMINARY assessment is in general concurrence with what seems to be the most common expectation for the winter - you can probably successfully read between the lines there). Been in that sector for about 10 years. Prior to that I was doing research met for almost 15 years. Damn, I'm getting old. Lol.

Thanks for the input, though I think you've misinterpreted me to an extent.

I certainly don't think the SSTs have no effect on circulation (see ENSO), however most of the literature I've read suggests warmer SSTs lead to additional lift/vertical instability, hence reduced surface pressures, w/ a corresponding visa-versa tendency over the colder SSTs. This is how we interpret MJO forcing, tropical cyclogenesis, etc.

I've never heard anyone suggest warm SSTs force sinking, stable air, nor can I find it in any literature. For the PDO idea to work, you need higher pressures over the warm SSTs, and lower pressures over the colder SSTs.

Can you maybe link me to some literature suggesting this? I'd love to learn more about this apparent phenomenon.

Furthermore, if the PDO were a "cause", what causes it to change? Why does it oscillate over time, lagging the ENSO and the AAM integral by 4-8 months? The ocean currents we observe are largely wind driven...so it all seems like circular reasoning to me.

Thanks again for the reply.

[millwx]

Thanks for the input, though I think you've misinterpreted me to an extent.

I certainly don't think the SSTs have no effect on circulation (see ENSO), however most of the literature I've read suggests warmer SSTs lead to additional lift/vertical instability, hence reduced surface pressures, w/ a corresponding visa-versa tendency over the colder SSTs. This is how we interpret MJO forcing, tropical cyclogenesis, etc.

I've never heard anyone suggest warm SSTs force sinking, stable air, nor can I find it in any literature. For the PDO idea to work, you need higher pressures over the warm SSTs, and lower pressures over the colder SSTs.

Can you maybe link me to some literature suggesting this? I'd love to learn more about this apparent phenomenon.

Furthermore, if the PDO were a "cause", what causes it to change? Why does it oscillate over time, lagging the ENSO and the AAM integral by 4-8 months? The ocean currents we observe are largely wind driven...so it all seems like circular reasoning to me.

Thanks again for the reply.

I can't link to that, because I'm not suggesting that.  Hehehe.

 

I think we're talking past each other a bit.  We actually agree about 90% of the way through the process.  My argument, incorporating the physics that you describe, which I actually pretty much agree with, is this:  The warm SSTs cause rising motion, lower pressures and lower heights.  In doing so, the result is DOWNSTREAM ridging.

 

Notice in my original reply, I stated that the ridging does NOT occur directly over the warmer SSTs.  The ESRL correlation plots bear this out.  Apologies... kinda newbyish on this board (been here a long time, but never inserted imagery before... it is not self-explanatory), so I cannot show the image.  But I encourage you to go to the ESRL page: http://www.esrl.noaa.gov/psd/data/correlation/ and plot it up yourself - look at the height anomaly correlation w.r.t. PDO.

 

PDO ridging does not occur anywhere near the SST max.  So, no one is (or SHOULD) be arguing that warm SSTs are forcing a ridge overhead.  If anyone IS arguing that, then, frankly, they don't even know what pattern a positive PDO imparts.  If there were a ridge, with the axis centered over the central GOA, it would NOT yield a cold Eastern U.S.  The downstream trough would be over the West/Rockies and the East would be warm.  That is not at all what is seen under a positive PDO.  So, any suggestion that there would be ridging aloft, over the warm GOA SSTs is simply misinformed.

 

But - and this AGREES with your point - as the ESRL plot shows, the warm SSTs, in fact, do NOT yield ridging over the GOA.  Indeed, on balance, the GOA has BELOW normal heights (though the extreme east, near the coast, pushes above a bit... so, the mean for the GOA is pretty neutral, but it probably slightly negative).  The peak height anomaly is FAR to the east, inland over Canada.

 

So... this in no way conflicts with your description of how the SSTs should interact with the atmosphere.  In fact, it largely agrees with your assessment.  The lone difference between what you are arguing and what I am arguing is that you are saying the PDO is a result of the pattern, while I am arguing that the PDO is influencing the pattern.  Because the ridge placement actually conforms to your dynamic assertions - which I agree with - I think my argument is largely supported.  And, as I also noted, the statistics support that theory in that the autumnal PDO phase is a fair predictor of the winter North American pattern (albeit, the lag is clearly not THAT great, because the winter PDO phase is a superior predictor).

 

And to your point about the wind flow providing the forcing... to THAT we are actually in complete agreement.  Yes, something must cause the PDO fluctuations.  And there are studies showing that it is wind flow.  So, I'm not arguing that there isn't some preceding pattern that will force the PDO in one direction or the other.  In fact, that's unquestionable, in my opinion... after all, it's not magic!  So, we're in total agreement there.  The question - and our disagreement - is this... once the PDO is established, is that a significant influence on the subsequent weather patterns.  In my studies and estimation, the answer is a clear-cut, yes.

 

As an aside, as certain as I am of this, I nonetheless approach this with an open mind.  The beauty of meteorology is that our understanding is always changing.  It's a "living" science.  Take for example the relationship between the ENSO and the NAO.  Bluntly, I was unaware of ANY such relationship.  But recently, via their work on the GloSea5 model, the UKMET office discovered a connection between autumnal El Nino events and winter negative NAOs.  Even they punted on the issue of why... they said it was a matter for another publication (though they conjectured that it had to do with Hadley cell evolution).  We're always learning more... I've been wrong a million times before... and maybe I'm wrong on this too.  But, at least as of now, I've seen no evidence to the contrary and, in fact, your argument (warm SSTs should cause lower pressures/heights) is actually supportive of this notion (since that should impact downstream ridging, which is precisely what is seen).  BTW, these are perhaps some of the most complex and intriguing issues (sea-air interactions) to try to deal with in monthly/seasonal forecasting.  I don't think anyone understands them fully.  I've been doing this for almost 25 years and I sure don't.

[StudentOfClimatology]

Thanks, I really enjoy your posts. Please stay!

I went ahead and plotted the data in accordance to the the PDO.

I think you might be misinterpreting what the ESRL graph is saying, or perhaps I am. I believe it's highlighting the seasonal correlation w/ the PDO, not height anomalies themselves...so I reversed the color table to try and make this point less fuzzy.

The correlation differentials are largely centered right over the N-PAC:

Of course, NOAA tends to do this much better than me. Here are images depicting the typical PDO phases:

[millwx]

Thanks, I really enjoy your posts. Please stay!

I went ahead and plotted the data in accordance to the the PDO.

I think you might be misinterpreting what the ESRL graph is saying, or perhaps I am. I believe it's highlighting the seasonal correlation w/ the PDO, not height anomalies themselves...so I reversed the color table to try and make this point less fuzzy.

The correlation differentials are largely centered right over the N-PAC:

Of course, NOAA tends to do this much better than me. Here are images depicting the typical PDO phases:

 

Believe me, I'm not ragging on you at all with my disagreement.  I *love* this discussion.  One thing I hate about this board is the arrogant ignorance of some amateurs.  But one thing I *love* about this board is that some of the amateurs here are more well educated than some mets (don't get me started on many mets' using inappropriate LINEAR correlation data on ENSO to assume that El Nino = warm for the winter; many "amateurs" on here have gotten wise to that one already, while many professional mets still stick to that fallacy)!  I have no idea whether you're an amateur or a pro... but, either way, you're in the latter camp... clearly well versed, and I appreciate that.  I'm having and honest, up front, blunt, disagreement with you.  I'm not being arrogant (read: JB/DT) or disrespectful towards you.  And, in fact, I am in 90% agreement with you.

 

Now, with that, I'm gonna disagree with you again.  Lol!  I honestly don't know what you mean by me misinterpreting the ESRL data.  Your ESRL plot shows EXACTLY what I'm saying.  You've reversed the sign on your plot... blues/purples are positive 500mb height anomalies (for the record, I didn't mention using 500mb in my reply to you... but that is, in fact, what I meant... thanks for not confusing matters and using something else, lol).  The maximum positive height anomaly is focused over interior Canada.  Admittedly, when I did the plot - on a different projection & contour interval - it appeared even a bit more inland.  Perhaps that's why you think I'm misinterpreting?  But even on your map, the maximum positive height anomaly is clearly inland over Canada... well upstream of where the peak SST anomalies would be.  Meanwhile, though the NEGATIVE height anomalies (orange shading) are NOT focused over the maximum SST anomalies, they are at least centered over what is most certainly the maximum positive SST gradient.

 

Again, I'd tell you that we're in complete agreement 90% of the way through this.  I concur with 100% of what you say regarding the mechanical wind forcing mechanisms AND the thermodynamics of what's happening above the warm SSTs.  And, by that token, you even agree that those warm SSTs are, in fact, having some influence on the atmosphere.  So, our only disagreement is on the final step.  And I think that ESRL plot backs me up... and I appreciate you including it (once I become more adept, I'll figure out how to include those plots myself)... the peak ridging is occurring well downstream of the peak positive SST anomalies (for the record, I'm assuming the peak positive SST anomalies are in the central GOA... that's not necessarily a certainty given the manner in which the PDO is measured... but that should be approximately a fair estimation).

 

Let me just re-emphasize that we do agree for the most part.  Anyone arguing that warm SSTs impart ridging overhead is completely lost on this... it is neither thermodynamically reasonable, nor does it comport to the standard PDO pattern.  The only reasons I spoke up to dispute you is... 1) I do think the resultant SST anomalies do have a large influence on the pattern, and I think logic and statistics support this and 2) this is a major area of study for me... while most energy mets do seasonal forecasting almost as an aside, I happen to work for a company that really puts their money where their mouth is... so, this is a keen area of interest for me, and your post really piqued my interest. 

[StudentOfClimatology]

Thanks, I too have enjoyed this investigation.

I guess I'm a bit confused now, though. In the +PDO phase, the mean clearly features a vortex/low heights over the N-PAC. In the -PDO phase, the mean is strongly biased towards a N-PAC ridge. These are roughly in the vicinity of the PDO anomaly. The pressure gradients are what drive the flow, correct?

During winter 2013-14, that monster ridge sat right over the N-PAC, and warmed the SSTs beneath it. The ridging extended all the way from the Aleutians, to the West Coast of North America.

[wildweatherman179]

If I believe correctly, the positive sst anomalies existed as early as the 1st week of July 2013. I do not recall the persistent ridge being in place at that time. I sincerely apologize for inserting myself into your discussion but I am an observer of this as well who believes it to be a cause of a pattern in late fall/winter versus it being an effect.

[StudentOfClimatology]

If I believe correctly, the positive sst anomalies existed as early as the 1st week of July 2013. I do not recall the persistent ridge being in place at that time. I sincerely apologize for inserting myself into your discussion but I am an observer of this as well who believes it to be a cause of a pattern in late fall/winter versus it being an effect.

No worries, please join if you feel inclined.

However, that ridge did exist well before then. Here are the 500mb heights from January 2013 to June 2013.

The ridging actually started in January 2013, after the major SSW event led to a cooling of the equatorial stratosphere. This set off a major MJO wave, which beat back the Niña-esque Walker Cell, and eventually turned the global circulations on their head...or so I believe.

[StudentOfClimatology]

Also, notice how the SSTs responded to the ridging over several months. Went from a classic negative PDO signature in January 2013 to a muddled stew of warmth by June 2013:

Mid-Jan:

Mid-Feb

Mid-Mar:

Mid-Apr:

Mid-May:

Mid-June:

[millwx]

No worries, please join if you feel inclined.

However, that ridge did exist well before then. Here are the 500mb heights from January 2013 to June 2013.

The ridging actually started in January 2013, after the major SSW event led to a cooling of the equatorial stratosphere. This set off a major MJO wave, which beat back the Niña-esque Walker Cell, and eventually turned the global circulations on their head...or so I believe.

 

Indeed, but check out the SST anomaly at that time.  The max positive SST anomaly was NOT in the GOA... it was southwest of there and gradually shifted towards the GOA.  So, once again, the ridge was upstream... just as the correlations indicate.  So, we really are in zero disagreement here in terms of the raw data.  The ridge was, in fact, west of the typical +PDO ridge in 2013-14... very much because the +SST anomaly also was.  This SW displacement of the SST anomaly bled over into the Mantua box and provided a misleadingly negative PDO (see: http://jisao.washington.edu/pdo/PDO.latest).  It's one of the reasons (not trying to blow my own horn, just stating a fact) I nailed my seasonal forecast... I saw this immense warm pool migrating towards the GOA.  Too many mets blindly follow the indices without actually looking at what's physically going on.

 

Anyway, as you can see there, the PDO was NEGATIVE last year, because the +SST anomaly was a little too far west.  That's why your Z500 anomaly plot for last year has the positive anomaly centered well west of the normal +PDO center.  But, it was just far enough east - and migrating east over time - to allow for a cold winter Midcon/East.  Last season is a poor example if you just blindly look at the PDO index, because it wasn't even positive.  But, if you actually look at the SST anomalies, it still fits perfectly...

 

...e.g., your Z500 anom plot above is from Jan to Jun 2013.  Taking the midpoint (again, apologies for just providing the link, not the image), here's the late March SST anomalies: http://www.ospo.noaa.gov/data/sst/anomaly/2013/anomnight.3.28.2013.gif  The peak SST anomalies are (roughly... it's a pretty broad area) south of the Alleutians.  The ridge is, from your plot, and very much as expected... downstream... centered over the middle of (or perhaps, most accurately, the SSE portion of) the GOA.

 

No contradictions there.  No surprises.  The only real surprise to me is, using the dynamics you describe (which, as I've said, I completely agree with), is that the warm SSTs struggle to produce a low Z500 anomaly.  But, arguably, the heat imparted - expanding the air - is keeping something of an equilibrium, not allowing for lower heights over the warm water.  That's purely conjecture though.  But it makes sense, as the relative height anomalies do fit the dynamic expectations perfectly (ridging downstream).  Bottom line... I don't have all the answers either.  But I certainly see nothing abnormal about last year... as normal, the ridging was upstream of the warm SSTs.

[millwx]

Also, notice how the SSTs responded to the ridging over several months. Went from a classic negative PDO signature in January 2013 to a muddled stew of warmth by June 2013:

Mid-Jan:

Mid-Feb

Mid-Mar:

Mid-Apr:

Mid-May:

Mid-June:

 

Our replies crossed each other.  See my previous response.  There is absolutely nothing surprising about this under my explanation.  The ridge was downstream of the max SST anomaly.  The ONLY thing I will grant you is, if you do your ESRL Z500 anomaly for winter 2013-14 (again, sorry, I'd show it here if I was smart enough, lol) you will see that the peak 500 anomaly does NOT migrate East well, if at all, with the SST migration.  So, as that SST anomaly pushed ENE into the GOA, the Z500 anomaly did not shift inland into Canada.

 

However, given the Z500-PDO correlations we've shown above, that is obviously the exception to the rule (that is, the peak +Z500 anomaly is well inland over Canada with a +PDO).  So, I've honestly still seen nothing that alters my opinion.  In fact, everything I've seen so far, with the exception of the one aforementioned caveat, reinforces my interpretation... warm NPac SSTs cause downstream ridging.

[GaWx]

I must say that this is the most interesting PDO discussion as to how it typically affects the wx pattern I have ever read! This may solve some of the chicken-egginess that has bothered me at times about the PDO. I initially learned a lot about SST's effects on weather patterns from JB. This discussion is giving me a bit of a different angle on the same idea. Thanks especially to Millwx & S of C. Millwx, I hope you post much more often!

[StudentOfClimatology]

Indeed, but check out the SST anomaly at that time. The max positive SST anomaly was NOT in the GOA... it was southwest of there and gradually shifted towards the GOA. So, once again, the ridge was upstream... just as the correlations indicate. So, we really are in zero disagreement here in terms of the raw data. The ridge was, in fact, west of the typical +PDO ridge in 2013-14... very much because the +SST anomaly also was. This SW displacement of the SST anomaly bled over into the Mantua box and provided a misleadingly negative PDO (see: http://jisao.washington.edu/pdo/PDO.latest). It's one of the reasons (not trying to blow my own horn, just stating a fact) I nailed my seasonal forecast... I saw this immense warm pool migrating towards the GOA. Too many mets blindly follow the indices without actually looking at what's physically going on.

Anyway, as you can see there, the PDO was NEGATIVE last year, because the +SST anomaly was a little too far west. That's why your Z500 anomaly plot for last year has the positive anomaly centered well west of the normal +PDO center. But, it was just far enough east - and migrating east over time - to allow for a cold winter Midcon/East. Last season is a poor example if you just blindly look at the PDO index, because it wasn't even positive. But, if you actually look at the SST anomalies, it still fits perfectly...

...e.g., your Z500 anom plot above is from Jan to Jun 2013. Taking the midpoint (again, apologies for just providing the link, not the image), here's the late March SST anomalies: http://www.ospo.noaa.gov/data/sst/anomaly/2013/anomnight.3.28.2013.gif The peak SST anomalies are (roughly... it's a pretty broad area) south of the Alleutians. The ridge is, from your plot, and very much as expected... downstream... centered over the middle of (or perhaps, most accurately, the SSE portion of) the GOA.

No contradictions there. No surprises. The only real surprise to me is, using the dynamics you describe (which, as I've said, I completely agree with), is that the warm SSTs struggle to produce a low Z500 anomaly. But, arguably, the heat imparted - expanding the air - is keeping something of an equilibrium, not allowing for lower heights over the warm water. That's purely conjecture though. But it makes sense, as the relative height anomalies do fit the dynamic expectations perfectly (ridging downstream). Bottom line... I don't have all the answers either. But I certainly see nothing abnormal about last year... as normal, the ridging was upstream of the warm SSTs.

Okay, let's avoid the "downstream" problem altogether, and use 1000mb geopotential heights instead of 500mb geopotential heights.

Using near-surface pressures, the hypothetical SSTA forcing should exist right over the SSTs, or at least very close to the SSTs.

However, we see that this is not the case at all. It appears that, once again, the maximum surface pressures do not sync up with the supposed SST forcings:

[wildweatherman179]

I am in 100 percent agreement with millwx on this and everyone else seems to disagree. It would be much like proposing the question of cause versus effect of El Niño/La Nina.

[StudentOfClimatology]

I am in 100 percent agreement with millwx on this and everyone else seems to disagree. It would be much like proposing the question of cause versus effect of El Niño/La Nina.

ENSO is also primarily wind-driven. Look what happened to the developing Niño with the lack of WWB activity this year...it fizzled out. The dynamics are no different as far as PDO SSTs are concerned...the Pacific Ocean doesn't just decide to flip it's PDO randomly...it needs to be forced to do so.

Let's make this easy. I have plotted SSTs and SLP data each month from January-May 2013. The strong N-PAC ridging seems to have forced the warm SSTs...not the other way around.

January:

February:

March:

April:

May