Medium Range Discussion Winter 2011-12

[ORH_wxman]

You don't think the pattern changes the SSTAs? Knowing ENSO precedes changes in the PDO? The -AO/-NAO pattern I'd think would enhance the -PDO North Pacific warm pool with the more poleward Aleutian ridge and -NAO block "feeding back" in flow, no? Maybe that is why the -AO is much more frequent in the -PDO, with long +AO periods rarely occuring except early in the -PDO phases. With the +PNA we have seen this winter [[and it looks to continue]] with the -PDO what would be creating that anomaly? The pattern over the North Pacific still argues to represent the -PDO "look" but the ridge is more elongated with the strong +AO which is why I think powerful +AO or strong Polar Vortexes usually do not coincide with a -PNA.

I don't disagree on the initial displacement of the Polar Vortex before the potential split, but how can a long range EPO or Polar Vortex config forecasts be used with any confidence right now? The SIberian snowcover count in October was near average overall, it was below average early on I think but towards the last week of October and into November it went above average if I remember correctly.

AO and PDO

Disagree with this...it definitely looks like we will be entering a -PNA period for the latter part of January and probably into February. GEFS are trying to keep it more positive but I think that flies in the face of typical Nina/-PDO climo and flies in the face of the Euro ensembles which have it going negative. A flexed Aleutian ridge teleconnects pretty good to a -PNA as well.

[usedtobe]

Disagree with this...it definitely looks like we will be entering a -PNA period for the latter part of January and probably into February. GEFS are trying to keep it more positive but I think that flies in the face of typical Nina/-PDO climo and flies in the face of the Euro ensembles which have it going negative. A flexed Aleutian ridge teleconnects pretty good to a -PNA as well.

plus usually when you get high latitude ridging it retrogrades to the west which also would favor a -PNA. The cross polar flow means more cold air should get into the conus but it likely will be aimed west. You guys could do OK, south of 40N I could see us still staying warm even with move shots of cold air.

[donsutherland1]

At this point in time, the idea that the eastern half of the U.S., along with southern Ontario and Quebec, will see the first half of January average above to much above normal in terms of temperatures looks to be on track. The farther north one goes, the warmer the anomalies will be during this period in time.

Afterward, it appears that the major teleconnection indices will undergo a change. It still remains unlikely that the kind of regime change that is needed to bring and sustain severe cold in the areas experiencing the warmth is likely during the January 16-23 timeframe. The turn toward colder readings is likely to be gradual. As a result, much of the East will likely remain at least somewhat milder than normal during that timeframe, but pockets of near normal readings, particularly in the Southeast may occur courtesy of a transient cold shot. Stronger and more sustained cold might be building into the Northern Plains from western Canada and that could be sufficient for that part of the U.S. to have colder than normal readings for the period.

Here are the temperature anomalies for all days during January 15-25 period (1950-2011) during La Niña events with ENSO R3.4 anomalies in the -1.5°C to -0.7°C range, AO in the -2.00 to 0.00 range and PNA in the -1.00 to +0.25 range:

If one looks at the objective analogs generated by the GFS ensembles (centered around 1/17), among the years showing up are 1954 and 1984. Both years saw very warm February anomalies. The raw temperature data for all the years generated saw February have a mean temperature that was close to normal in the Mid-Atlantic region. However, if one adjusts the readings for the observed warming that has occurred by standardizing the base period to the current one (1981-10), the outcome was 1°-2° above normal.

Both the GFS and ECMWF take the MJO through Phase 8 (ECMWF keeps it weak and in the so-called "circle of death"). The GFS goes into Phase 1. If the timing on the GFS is correct and if the MJO progresses at a fairly average pace with no "short cuts" or reversals--two big "ifs"--the MJO could return to Phase 4 sometime during the first 7-10 days in February. Phases 4-7 are typically warm in the East, with Phases 6-7 being cold in the West (typical PNA- pattern). The bottom line is that the MJO forecasts might also be offering a hint of a plausible warm outcome in February.

The CFSv2 ensemble system is also hinting at a warm outcome in February. Run-to-run continuity has been very good for North America.

The actual outcome for February will depend on the continuing evolution of the La Niña and the teleconnections. For now, there are some hints from the objective analogs and also MJO forecasts that a mild February, at least in the East, is a possibility. Things can still change, as February is well in the future. What does appear to be a higher confidence idea is that even after mid-month, the January 16-23 timeframe will likely see milder readings outduel cooler ones in areas that are likely to have been warm to very warm during the first half of this month.

[usedtobe]

At this point in time, the idea that the eastern half of the U.S., along with southern Ontario and Quebec, will see the first half of January average above to much above normal in terms of temperatures looks to be on track. The farther north one goes, the warmer the anomalies will be during this period in time.

Afterward, it appears that the major teleconnection indices will undergo a change. It still remains unlikely that the kind of regime change that is needed to bring and sustain severe cold in the areas experiencing the warmth is likely during the January 16-23 timeframe. The turn toward colder readings is likely to be gradual. As a result, much of the East will likely remain at least somewhat milder than normal during that timeframe, but pockets of near normal readings, particularly in the Southeast may occur courtesy of a transient cold shot. Stronger and more sustained cold might be building into the Northern Plains from western Canada and that could be sufficient for that part of the U.S. to have colder than normal readings for the period.

Here are the temperature anomalies for all days during January 15-25 period (1950-2011) during La Niña events with ENSO R3.4 anomalies in the -1.5°C to -0.7°C range, AO in the -2.00 to 0.00 range and PNA in the -1.00 to +0.25 range:

If one looks at the objective analogs generated by the GFS ensembles (centered around 1/17), among the years showing up are 1954 and 1984. Both years saw very warm February anomalies. The raw temperature data for all the years generated saw February have a mean temperature that was close to normal in the Mid-Atlantic region. However, if one adjusts the readings for the observed warming that has occurred by standardizing the base period to the current one (1981-10), the outcome was 1°-2° above normal.

Both the GFS and ECMWF take the MJO through Phase 8 (ECMWF keeps it weak and in the so-called "circle of death"). The GFS goes into Phase 1. If the timing on the GFS is correct and if the MJO progresses at a fairly average pace with no "short cuts" or reversals--two big "ifs"--the MJO could return to Phase 4 sometime during the first 7-10 days in February. Phases 4-7 are typically warm in the East, with Phases 6-7 being cold in the West (typical PNA- pattern). The bottom line is that the MJO forecasts might also be offering a hint of a plausible warm outcome in February.

The CFSv2 ensemble system is also hinting at a warm outcome in February. Run-to-run continuity has been very good for North America.

The actual outcome for February will depend on the continuing evolution of the La Niña and the teleconnections. For now, there are some hints from the objective analogs and also MJO forecasts that a mild February, at least in the East, is a possibility. Things can still change, as February is well in the future. What does appear to be a higher confidence idea is that even after mid-month, the January 16-23 timeframe will likely see milder readings outduel cooler ones in areas that are likely to have been warm to very warm during the first half of this month.

Don, according to Stu Osto and Joe Lundberg the euro weeklies also forecasting that late Jan into Early Feb will average warmer than normal.

[donsutherland1]

Don, according to Stu Osto and Joe Lundberg the euro weeklies also forecasting that late Jan into Early Feb will average warmer than normal.

That's definitely something to consider. It might be awful, but even the coldest period in January could still wind up somewhat above normal. I hope that won't be the case.

[Met1985]

Great write up Don. Not what a lot of people are looking for but it is what it is.

[Snowstorms]

That's definitely something to consider. It might be awful, but even the coldest period in January could still wind up somewhat above normal. I hope that won't be the case.

Amazing write-up man. At this point in time the models seem to bring the MJO into the circle but there continues to be quite the spread on the MJO forecasts with some members showing it entering Phases 3-6 in early February which could spell yet another torch to the seemingly endless Fall.

Based on NATL. SST's I don't think we can develop a prolonged period of a -NAO anomaly thru the reminder of this Winter but I argue against this point for March as I think March will end up quite cold across the East relative to normal.

The deeply negative PDO anomaly/La Nina anomaly in the Pacific calls for a continuation of a -PNA anomaly and perhaps a developement of a -EPO anomaly as the Aleutian Ridge anomaly looks to build back mid month. As for the second half of January I do think the second half will feature more cold shots than what we've been seeing but given the gradient pattern that may set-up, its quite possible areas West of the Lakes will end up near normal-slightly below normal normal depending how cold it gets to erase the extreme warm anomalies within the first 10-12 days with possible cold anomalies building around Jan 15th.

I think 99-00, 74-75, 64-65, 49-50 and/or 55-56 are decent analogues for the remainder of the Winter. Again these analogues are useful for temperature anomalies not precip IMO.

Surely Winter is no where to be seen ANYWHERE across the board, this is just astounding. I mean Calgary the other day was 60F, unbelievable! This Winter f***king sucks!

[winterymix]

The European model holds onto La Nina at least until early springtime.

Klaus Wolter's group is even more assertive about La Nina conditions hanging

on for a while.

. La Niña appears to have staged a comeback similar to 2008, and consistent with expectations formulated right here more than one year ago: big La Niña events have a strong tendency to re-emerge after 'taking time off' during northern hemispheric summer. Based on current atmosphere-ocean conditions, I believe the odds for this La Niña event to continue right through early spring (March-April 2012) are just about 50%. Beyond that, it is worth noting that of the ten two-year La Niña events between 1900 and 2009, four ended up as a three-year event, so I would put the odds for this to occur in 2012-13 at 40% right now.

[Srain]

Meanwhile Winter Storm Watches are hoisted for New Mexico and Special Weather Statements are flying for winter weather from El Paso, Midland/Odessa to Amarillo.

[40/70 Benchmark]

I'm numb at this point....Don's post would have devastated me a month or so ago, but regardless....this dreadful season is half way over.

The CFS can't take that away from us.

[BethesdaWX]

Disagree with this...it definitely looks like we will be entering a -PNA period for the latter part of January and probably into February. GEFS are trying to keep it more positive but I think that flies in the face of typical Nina/-PDO climo and flies in the face of the Euro ensembles which have it going negative. A flexed Aleutian ridge teleconnects pretty good to a -PNA as well.

Maybe you're right and I'm wrong, I'm just not sold on the idea of any worthwhile -PNA anytime soon. "Climo" definitely has not worked out well at all this winter, which La Nina winters with warm Decembers and strong +AO from November through January seem to come in a decadal cycle, and in the -PDO phase cycle, all Ninas that torched over most of the US in October, November, December and January, except 1, have seen a flip in February sometime, and there are many of those years that all occur just before the solar maximum.

Weak and/or mixed QBO phases seem to occur when the Interplanetary Field is weak and ready to flip, which happened in (1956/57, 1967/68, 1978/79, 1989/90, 1999/00), which have all come up as good analogs this winter.

I don't usually look at ensembles with any seriousness after day 7 especially for the MJO which varies wildly, nor use long range models to forecast during a period when a pattern change may be in store because often it isn't picked up until the 6-10 day range if it is of vague causation.

[Damage In Tolland]

Don...most of the energy mets/traders are going balls to wall cold for late Jan and much of Feb. AO is tanking and it looks like we'll have Cahir's connection along with cross polar flow. You may want to rethink things

[DaculaWeather]

Don...most of the energy mets/traders are going balls to wall cold for late Jan and much of Feb. AO is tanking and it looks like we'll have Cahir's connection along with cross polar flow. You may want to rethink things

OK... new term for me. Can you please explain Cahir's connection...? But I'm with you all the way!

[donsutherland1]

Don...most of the energy mets/traders are going balls to wall cold for late Jan and much of Feb. AO is tanking and it looks like we'll have Cahir's connection along with cross polar flow. You may want to rethink things

My thinking is only through 1/23 and recent runs of the GFS have now come in line with that scenario. There is a possibility that the last 10 days of January/first week or so of February could be the coldest period this winter, though that does not necessarily mean sustained cold, just the coldest average period relative to normal. That is not a slam dunk e.g., if the PNA- sets in with a vengeance, the cold would be focused in the West. The East should be colder, on average, than it has been this winter if things work out, but the worst of the cold might stay to the West.

As for February, the MJO progression would argue against much of the month being cold. It's still very early, so much can change. But this has been a winter where cold forecasts e.g., for December, have been shattered very badly. In fact, even the first week of January that was modeled very cold is going to average warmer than normal despite a short cold shot. Strong warmth is outdueling the cold. Not every winter flips dramatically like 2006-07, which was not a La Niña winter, had a PDO+ with persistent PNA+, and an AO that went negative. All that had to happen in that setup was for blocking to return and then the cold would come.

It's not so clear-cut this time around. Winter 2011-12 is a La Niña winter with a strong PDO- (correlates to more frequent PNA-). Unlike 2006-07, there is no strong assurance that the PNA will be positive during any episodes of blocking that might show up. That would lead to a very different outcome.

[NorEaster27]

Don...most of the energy mets/traders are going balls to wall cold for late Jan and much of Feb. AO is tanking and it looks like we'll have Cahir's connection along with cross polar flow. You may want to rethink things

wrong, no one is going for big cold. Looks very transient 1-3 day cold shots followed by warm ups and rain.

[Ginx snewx]

OK... new term for me. Can you please explain Cahir's connection...? But I'm with you all the way!

Theory that, when a ridge develops over Central Russia from the Caspian Sea North towards the Urals, it leads to a positive PNA over NA a week later.

[DaculaWeather]

Theory that, when a ridge develops over Central Russia from the Caspian Sea North towards the Urals, it leads to a positive PNA over NA a week later.

Thank you sir!

[donsutherland1]

I argue against this point for March as I think March will end up quite cold across the East relative to normal.

At this time, I lean toward a cooler than normal March. So, meteorological spring could start on the cool side. Of course, that's way out there and if some of what I expect to take place doesn't, things could change.

Surely Winter is no where to be seen ANYWHERE across the board, this is just astounding. I mean Calgary the other day was 60F, unbelievable! This Winter f***king sucks!

I saw that. I share those sentiments. Little is more painful than a warm and relatively snowless winter. Hopefully, there will be at least one significant snowstorm from the Great Lakes into Ontario. Farther east, I do not believe a KU storm is likely this winter, but the Midwest into Ontario and perhaps even parts of Quebec can salvage something.

[donsutherland1]

A quick point to illustrate the importance of a PNA+. The PNA+ is the most important teleconnection for the Mid-Atlantic region when it comes to severe cold during La Niña events. As the temperatures have warmed in recent decades, its importance has grown.

As an example, I defined severely cold days as those days on which the minimum temperature fell below 10°F in Philadelphia during any month when the ENSO Region 3.4 anomaly was -0.50°C or lower. I used the 1951-1980 base period (33.3° mean December-February temperature and 31 severely cold days) and compared it to the 1981-2010 base period (35.4° mean December-February temperature and 22 severely cold days). The former period saw 71% of severely cold days occur when the PNA was positive. The latter saw 77% of severely cold days occur when the PNA was positive.

The scatter diagrams for the two base periods are below:

[Feb]

My thinking is only through 1/23 and recent runs of the GFS have now come in line with that scenario. There is a possibility that the last 10 days of January/first week or so of February could be the coldest period this winter, though that does not necessarily mean sustained cold, just the coldest average period relative to normal. That is not a slam dunk e.g., if the PNA- sets in with a vengeance, the cold would be focused in the West. The East should be colder, on average, than it has been this winter if things work out, but the worst of the cold might stay to the West.

As for February, the MJO progression would argue against much of the month being cold. It's still very early, so much can change. But this has been a winter where cold forecasts e.g., for December, have been shattered very badly. In fact, even the first week of January that was modeled very cold is going to average warmer than normal despite a short cold shot. Strong warmth is outdueling the cold. Not every winter flips dramatically like 2006-07, which was not a La Niña winter, had a PDO+ with persistent PNA+, and an AO that went negative. All that had to happen in that setup was for blocking to return and then the cold would come.

It's not so clear-cut this time around. Winter 2011-12 is a La Niña winter with a strong PDO- (correlates to more frequent PNA-). Unlike 2006-07, there is no strong assurance that the PNA will be positive during any episodes of blocking that might show up. That would lead to a very different outcome.

While i respect your opinion, and i am starting to have some doubts myself about how much colder it does get, you are on shaky ground using the GFS two weeks out to back up your forecast.

[Ellinwood]

While i respect your opinion, and i am starting to have some doubts myself about how much colder it does get, you are on shaky ground using the GFS two weeks out to back up your forecast.

Do you mean the very same Euro which in an early 6-10 outlook this past week had me getting 18" of snow? I'm not to concerned with one run of the euro. Besides i hear the Euro Ensembles are beginning to look a bit better in the long range.

I believe the last two weeks of January and most of February will see a big turn around here in the east. I believe you are in the warm camp for February but i believe February could actually be a very cold and stormy. Of course if i'm wrong, this winter will have been one of the biggest duds in history for the east.

So Don can't use the Euro or the GFS to support his ideas, and now when he goes cold for the end of Jan into early Feb, a period in which you were also thinking there would be cold, you turn around and tell Don that it's not going to be that cold. Within these arguments, Don has made many posts to defend his arguments, and you have provided zero evidence to support your conclusions.

You're awesome.

[keggwx]

I'm not completely convinced that the PNA will be all that negative. Especially when the d8-10 models are pretty clear with a more impressive ridge from AK to the Arctic which risks PV displacement towards the Hudson.

[Srain]

Once again, as we saw in December, these closed cold core upper lows are a forecasting challenge at best. This morning we see Winter Storm Watches hoisted for New Mexico with Special Weather Statements for winter weather from El Paso, Midland/Odessa, to Amarillo. San Angelo has joined in the question of whether they will see wintery mischief across their area and even Dallas/Ft Worth is mentioning the possibility of a wintry mix to their W as the upper low treks E. Further S, rains and storms look likely beginning late Sunday into Tuesday morning. The SPC is mentioning even a possible tornado or two for S Texas as a Coastal Low develops. It does appear that heavy rains and storms are likely for Central/SE TX Sunday night into Monday night/early Tuesday morning. There still remain some uncertainty on the exact track of the U/L and precip could linger into Tuesday as the closed cold core upper low passes. The focal point for heavy rains will be along a stalled frontal boundary draped across Central/SE TX and wide spread 1-2 inch amounts, with isolated 4+ inch amounts possible where any training of heavy showers/storms develop.

A stronger push of colder air should follow on Thursday as a complex Winter Storm develops near the Great Lakes/Upper Mid West and a Canadian front dives S into the Plains in the wake of our passing storm early next week. Model volatility returns yet again with what happens with yet another upper low to our W on Wednesday/Thursday and just when that feature will eject E. Sound familiar? Various solutions and day to day, run to run solutions are offered by the various guidance and a very changeable forecast lies ahead regarding late next week. What is developing via guidance is heights increasing near/over Alaska and a break down of the Alaska Vortex that has brought record cold and snows to Cordova/Prince William Sound and cold temps are pushed into Western Canada and Arctic high pressure builds in the 1048-1055+ range and extends to the N Pole.

What often happen when a whole sale pattern change occurs are guidance flip flops and various solutions will change like the hands on a clock. It does appear we are entering a period where cold air intrusions are becoming more likely as we head into mid January. There still remain indications the a favorable MJO in phase 7-8, albeit weak will allow tropical forcing to keep the Pacific pattern active for us before relaxing later this month. A -AO/-EPO regime with a waffling +/-PNA is conducive to a cold and active pattern for the Western 1/2 to 2/3 of the North America while the East Coast remains warm with a +NAO or lack of Greenland blocking. The SE ridge tends to hold the cold air intrusions W as storm systems trek NE into the Ohio Valley or W of the Appalachians. All that said, stay tuned! We are entering a very changeable period and cold air intrusions well S into Mexico cannot be ruled out as a cross Polar flow may develop and depending on exactly where the Alaska Vortex is displaced, or takes up shop in Canada. My hunch is we are entering a very interesting period.

[Ellinwood]

Well i see my original post to you was deleted. By the way, how many times have you changed your monthly outlooks this winter?

I saw your original post, so don't worry about that. I issued my winter outlook once in August, made a mid-October update (which did not change from the August call that much), and I have issued a "final" forecast for each month as they come up (ie my final Dec forecast was made Nov 31st and my final Jan forecast was made Dec 31st). Two changes (with only one significant change) over a 5-6 month period.

As for your original reply, despite forecasters occasionally using the operational models to back up their thoughts, this does not mean they're incorrect. Other support from the ensembles and from using teleconnections has been provided in addition to discussing the operationals. While the operationals do not provide very accurate medium-range forecasts, they are sometimes useful in this range. It takes experience to know when an operational run does provide viable output, and when it does it can be integrated into the discussion.

I'm not completely convinced that the PNA will be all that negative. Especially when the d8-10 models are pretty clear with a more impressive ridge from AK to the Arctic which risks PV displacement towards the Hudson.

Agreed... the PNA has been forecast to go decently negative more than once this winter, but a notably -PNA signal has failed to appear since mid-November.

Over the last couple of days the Euro and GFS ensembles have been trending towards the more positive direction (EDIT: not into positive range as much as holding closer to neutral), which helps support this line of thinking.

[donsutherland1]

While i respect your opinion, and i am starting to have some doubts myself about how much colder it does get, you are on shaky ground using the GFS two weeks out to back up your forecast.

The GFS, specifically the change that has occurred in its extended range, was used to point to at least one model's shifting toward the idea I had posted. Earlier runs had been quite cold after mid-month (a few even hinted at a moderate snow event). I'm not counting on its precise anomalies, just noting its shift.

We'll see what happens in the end.

[Snowstorms]

At this time, I lean toward a cooler than normal March. So, meteorological spring could start on the cool side. Of course, that's way out there and if some of what I expect to take place doesn't, things could change.

I saw that. I share those sentiments. Little is more painful than a warm and relatively snowless winter. Hopefully, there will be at least one significant snowstorm from the Great Lakes into Ontario. Farther east, I do not believe a KU storm is likely this winter, but the Midwest into Ontario and perhaps even parts of Quebec can salvage something.

Most La Nina years I've analyzed have started a late spring across the East and most of them showed a cool and wet spring so it would seem reasonable to assume March wil end up colder than normal across the East but I'm not 100 % confident on that statement as I would like to see how February progresses first in terms of the teleconnection pattern.

The last time I saw a storm of over 10" was in 2007-08 so tell me what's there to be happy about lol? 2008-09 was a sick Winter, featured alot of overruning events but 2009-10/2010-11 were crap across my region despite last Winter achieving above normal snowfall here. Starting to focus on next Winter as a result.

Extreme pattern flips like in 06-07 arent always common in every winter that resembled that particular Winter but I do foresee a more Winter like pattern for the remainder of Winter. Its amazing how much difference one year makes in terms of the teleconnection pattern. I think 64-65 and 49-50 are decent analogues for Mid Jan-mid March.

[bluewave]

The Euro day 10 ensemble mean has the look of 1/17/50.

[Feb]

I saw your original post, so don't worry about that. I issued my winter outlook once in August, made a mid-October update (which did not change from the August call that much), and I have issued a "final" forecast for each month as they come up (ie my final Dec forecast was made Nov 31st and my final Jan forecast was made Dec 31st). Two changes (with only one significant change) over a 5-6 month period.

As for your original reply, despite forecasters occasionally using the operational models to back up their thoughts, this does not mean they're incorrect. Other support from the ensembles and from using teleconnections has been provided in addition to discussing the operationals. While the operationals do not provide very accurate medium-range forecasts, they are sometimes useful in this range. It takes experience to know when an operational run does provide viable output, and when it does it can be integrated into the discussion.

Agreed... the PNA has been forecast to go decently negative more than once this winter, but a notably -PNA signal has failed to appear since mid-November.

Over the last couple of days the Euro and GFS ensembles have been trending towards the more positive direction (EDIT: not into positive range as much as holding closer to neutral), which helps support this line of thinking.

Ok, thanks for the explanation. I just know from reading the boards some mets have always said don't put much into the operational runs in the long range. And as an example the 12z run has flipped colder and stormier in the long range compared to the 0z and 6z run. A lot of uncertainity for sure.

[KEITH L.I]

The Euro day 10 ensemble mean has the look of 1/17/50.

sort of fits in with this sad winter..49-50 however did have a decent february with some blocking..could be a great analog

[CoastalWx]

I saw your original post, so don't worry about that. I issued my winter outlook once in August, made a mid-October update (which did not change from the August call that much), and I have issued a "final" forecast for each month as they come up (ie my final Dec forecast was made Nov 31st and my final Jan forecast was made Dec 31st). Two changes (with only one significant change) over a 5-6 month period.

As for your original reply, despite forecasters occasionally using the operational models to back up their thoughts, this does not mean they're incorrect. Other support from the ensembles and from using teleconnections has been provided in addition to discussing the operationals. While the operationals do not provide very accurate medium-range forecasts, they are sometimes useful in this range. It takes experience to know when an operational run does provide viable output, and when it does it can be integrated into the discussion.

Agreed... the PNA has been forecast to go decently negative more than once this winter, but a notably -PNA signal has failed to appear since mid-November.

Over the last couple of days the Euro and GFS ensembles have been trending towards the more positive direction (EDIT: not into positive range as much as holding closer to neutral), which helps support this line of thinking.

I think though, that with an Aleutian high like that, it will have a tendency for troughing in sw Canada and into the Pac NW. That may give rise to more zonal flow or enhanced se ridging out ahead of it. However if the GEFS are right, it could retrograde enough to help form weak ridging across CA. The EC has also had a tendency to be too -PNA happy at times recently, but the pattern shows does seem to argue for some troughing in those areas mentioned earlier.