January 2017 Discussion & Observations

[donsutherland1]

34 minutes ago, frd said:

Don , regarding the SSW event that took place in Feb 1989,  as well as the late month Atlantic City and Norfolk snowstorm, do you know if the sequence of events leading up to that mimics this year so far?

In regards to the forecasted rising AO , and the portrayed 500 mb pattern that you metion above with the progression of the pattern like 1989 do you think it is possible that the upcoming SSW ( depending of course on the final outcomes ) could cause a similiar event later this Feb., or early March.

Thanks

 

January 1989 experienced a sudden stratospheric warming of the upper stratosphere, which appears similar to what is unfolding now (generally above 10 mb). If there’s a difference, so far the bulk of the warming this time around has been confined to above 2 mb. Wind reversal is only forecast to occur at 1 mb (1/20 ECMWF).

In 1989, the warming gradually propagated lower. The warming reached 30 mb by mid-February 1989 and around 100 mb near the start of March. 

1989 Zonal Temperature Anomalies:
http://www.cpc.ncep.noaa.gov/products/stratosphere/strat-trop/gif_files/time_pres_TEMP_ANOM_ALL_NH_1989.gif

The 1989 event was not sufficient to bring an end to the extreme AO+ of winter 1988-89.  Typically, one needs a much larger event and one that affects far more than the top 5 mb-10 mb of the stratosphere to have a chance dramatically alter the state of blocking (or prolong it, if the SSW is a response to strong blocking that preceded it, as can happen).

The AO briefly dipped below zero on March 4, 1989 (-0.318) for the first time since December 25, 1988. It then went positive and remained positive until April 15. March 4 was the only day in the December 26, 1988-April 14, 1989 period (110 days) with a negative AO figure.
 

[donsutherland1]

19 minutes ago, bluewave said:

It would be great to know specifically how the record -AO in March 2013 appears to have shifted the AO to a more positive state. I guess there is much about

the AO that we just don't understand yet. The 46 month period from June 2009 to March 2013 featured 30 out of 46 months with a -AO. The most recent

46 month stretch form April 2013 to January 2017 has experienced 29 out of 46 months with a +AO.

I agree. Much research needs to be done to better understand the AO, much less reliably forecast its state on timescales beyond about two weeks. Forecasting toward the end of two weeks is also challenging, as one has seen the ensembles shift quite a bit over short periods of time. 

[snowman19]

5 minutes ago, donsutherland1 said:

January 1989 experienced a sudden stratospheric warming of the upper stratosphere, which appears similar to what is unfolding now (generally above 10 mb). If there’s a difference, so far the bulk of the warming this time around has been confined to above 2 mb. Wind reversal is only forecast to occur at 1 mb (1/20 ECMWF).

In 1989, the warming gradually propagated lower. The warming reached 30 mb by mid-February 1989 and around 100 mb near the start of March. 

1989 Zonal Temperature Anomalies:
http://www.cpc.ncep.noaa.gov/products/stratosphere/strat-trop/gif_files/time_pres_TEMP_ANOM_ALL_NH_1989.gif

The 1989 event was not sufficient to bring an end to the extreme AO+ of winter 1988-89.  Typically, one needs a much larger event and one that affects for than the top 5 mb-10 mb of the stratosphere to have a chance dramatically alter the state of blocking (or prolong it, if the SSW is a response to strong blocking that preceded it, as can happen).

The AO briefly dipped below zero on March 4, 1989 (-0.318) for the first time since December 25, 1988. It then went positive and remained positive until April 15. March 4 was the only day in the December 26, 1988-April 14, 1989 period (110 days) with a negative AO figure.
 

Nice post. The 1989 SSW was much more impressive than what is being modeled currently for this year

[bluewave]

6 minutes ago, donsutherland1 said:

I agree. Much research needs to be done to better understand the AO, much less reliably forecast its state on timescales beyond about two weeks. Forecasting toward the end of two weeks is also challenging, as one has seen the ensembles shift quite a bit over short periods of time. 

It seems like the EPS and CMC ensembles have been doing a better job with the +AO than the GEFS. The GEFS has been constantly backing off

-AO forecasts since November the closer in time we get to the forecast time verifying.

 

[frd]

6 minutes ago, donsutherland1 said:

January 1989 experienced a sudden stratospheric warming of the upper stratosphere, which appears similar to what is unfolding now (generally above 10 mb). If there’s a difference, so far the bulk of the warming this time around has been confined to above 2 mb. Wind reversal is only forecast to occur at 1 mb (1/20 ECMWF).

In 1989, the warming gradually propagated lower. The warming reached 30 mb by mid-February 1989 and around 100 mb near the start of March. 

1989 Zonal Temperature Anomalies:
http://www.cpc.ncep.noaa.gov/products/stratosphere/strat-trop/gif_files/time_pres_TEMP_ANOM_ALL_NH_1989.gif

The 1989 event was not sufficient to bring an end to the extreme AO+ of winter 1988-89.  Typically, one needs a much larger event and one that affects for than the top 5 mb-10 mb of the stratosphere to have a chance dramatically alter the state of blocking (or prolong it, if the SSW is a response to strong blocking that preceded it, as can happen).

The AO briefly dipped below zero on March 4, 1989 (-0.318) for the first time since December 25, 1988. It then went positive and remained positive until April 15. March 4 was the only day in the December 26, 1988-April 14, 1989 period (110 days) with a negative AO figure.
 

Great info as always Don. Thanks

Makes you wonder about multi years trends in  AO, (and the NAO ) including the relationship to solar cycle, and the QBO. 

 

 

 

[Stormlover74]

Gray dreary and 43. I feel like it's been this way for the past week

[donsutherland1]

12 minutes ago, bluewave said:

It seems like the EPS and CMC ensembles have been doing a better job with the +AO than the GEFS. The GEFS has been constantly backing off

-AO forecasts since November the closer in time we get to the forecast time verifying.

 

They have. The GEFS has had a tendency to consistently forecast a lower AO than has materialized in its extended range forecasts during the winter. Perhaps the most recent upgrade had an impact on its winter season forecasts?

[uncle W]

Feb. 1st 1989 was 67 degrees in NYC...This year could be a different story come Feb. 1st...

[donsutherland1]

1 minute ago, uncle W said:

Feb. 1st 1989 was 67 degrees in NYC...This year could be a different story come Feb. 1st...

We will probably be colder than normal on 2/1, but it's afterward the GFS ensembles move toward the mean 2/1-15/1989 500 mean pattern. Such a pattern won't be as warm as a large part of January has been, but it is less snowy than Climo. We may need to cash in before 2/7. For now, the 6z GFS teased us with a "bomb." 

[uncle W]

23 minutes ago, donsutherland1 said:

We will probably be colder than normal on 2/1, but it's afterward the GFS ensembles move toward the mean 2/1-15/1989 500 mean pattern. Such a pattern won't be as warm as a large part of January has been, but it is less snowy than Climo. We may need to cash in before 2/7. For now, the 6z GFS teased us with a "bomb." 

I always thought March would be the snowiest month or have the largest snowfall...the way this winter is going that could happen...early March 1989 had a snowfall and cold shot before Spring sprung...

[weatherpruf]

1 hour ago, donsutherland1 said:

January 1989 experienced a sudden stratospheric warming of the upper stratosphere, which appears similar to what is unfolding now (generally above 10 mb). If there’s a difference, so far the bulk of the warming this time around has been confined to above 2 mb. Wind reversal is only forecast to occur at 1 mb (1/20 ECMWF).

In 1989, the warming gradually propagated lower. The warming reached 30 mb by mid-February 1989 and around 100 mb near the start of March. 

1989 Zonal Temperature Anomalies:
http://www.cpc.ncep.noaa.gov/products/stratosphere/strat-trop/gif_files/time_pres_TEMP_ANOM_ALL_NH_1989.gif

The 1989 event was not sufficient to bring an end to the extreme AO+ of winter 1988-89.  Typically, one needs a much larger event and one that affects far more than the top 5 mb-10 mb of the stratosphere to have a chance dramatically alter the state of blocking (or prolong it, if the SSW is a response to strong blocking that preceded it, as can happen).

The AO briefly dipped below zero on March 4, 1989 (-0.318) for the first time since December 25, 1988. It then went positive and remained positive until April 15. March 4 was the only day in the December 26, 1988-April 14, 1989 period (110 days) with a negative AO figure.
 

Was this a problem in the 80's in general? I can remember only a handful of serious events, and the 89 one was suppressed by a northwest wind if I remember correctly, acting like a big blow dryer; at the time it was a huge bust because no one in this region saw a flake.

[weatherpruf]

11 minutes ago, uncle W said:

I always thought March would be the snowiest month or have the largest snowfall...the way this winter is going that could happen...early March 1989 had a snowfall and cold shot before Spring sprung...

I don't remember the March event Unc, when was it and how much? I know I had the boat in and we were fishing the Raritan for winter flounder already. The hot spot was just off Prince's Bay.

[uncle W]

9 minutes ago, weatherpruf said:

I don't remember the March event Unc, when was it and how much? I know I had the boat in and we were fishing the Raritan for winter flounder already. The hot spot was just off Prince's Bay.

 

I have a video of that day...my daughter was two at the time...and now shes 29...Time flies...

 

[snowman19]

46 minutes ago, weatherpruf said:

Was this a problem in the 80's in general? I can remember only a handful of serious events, and the 89 one was suppressed by a northwest wind if I remember correctly, acting like a big blow dryer; at the time it was a huge bust because no one in this region saw a flake.

The 1980-1990 winters were extremely hostile to any high latitude blocking, especially Atlantic and arctic blocking. That entire time period was just awful for snow here. It was either cold and dry or warm and raining

[EastonSN+]

1 hour ago, donsutherland1 said:

We will probably be colder than normal on 2/1, but it's afterward the GFS ensembles move toward the mean 2/1-15/1989 500 mean pattern. Such a pattern won't be as warm as a large part of January has been, but it is less snowy than Climo. We may need to cash in before 2/7. For now, the 6z GFS teased us with a "bomb." 

Thanks Don. Its disappointing to see the good signals on the long range guidence evaporate. However, this has been the patter since the start of December. Good news is that we seem to cash in on each cold snap, and if one were to follow the pattern we should have another cold snap early to mid March. We have a decent shot at normal snowfall IMO.

[donsutherland1]

With regard to the predominant state of the Arctic Oscillation (% of days <0 or >0 during meteorological winter, the positive phase has dominated in 7 of the past 10 winters. Winter 2016-17 is all but certain to have a dominant positive phase, as well. Whether it has a super-dominant phase (80% or more days in a given state) remains to be seen. Since winter 1950-51, there have been 11 such cases:

1959-60 Negative: 83.5% days
1962-63 Negative: 87.8% days
1968-69 Negative: 80.0% days
1969-70 Negative: 92.2% days
1972-73 Positive: 81.1% days
1976-77 Negative: 93.3% days
1985-86 Negative: 87.8% days
1988-89 Positive: 98.9% days
1992-93 Positive: 83.3% days
2009-10 Negative: 97.8% days
2012-13 Negative: 83.3% days

All of the positive cases with a super-dominant positive phase saw 15 or more days where the AO was >0 in February. However, 1992-93 saw only 5 days on which the AO was +1.000 or above in February. 1972-73 had 13 and 1988-89 had all 28.

[Isotherm]

Pattern update:

The anticipated wave-1 increase via the tropospheric precursor pattern and concomitant MJO propagation support has led to an enhanced convergence of energy at the vortex, resulting in sufficient forcing to temporarily displace the stratospheric vortex from the center of the pole. The vortex will be pushed toward Greenland at 50-10hpa by D 10. However, after which, wave-1 convergence begins to decline, and with no follow-up wave-2 assault, and so the resultant outcome may be a near miss; namely, the reduction of zonal winds at 60N/10hpa to weakly positive levels (no reversal). Right now, it appears the wave driving will be sufficient to induce a mean zonal wind reversal at the top of the atmosphere (1hpa), but not further down. Even in the case that zonal winds are temporarily reversed at 10hpa, there are a couple of significant issues: 1) This potential displacement event will likely not be one which results in the subsequent destruction of the vortex, but rather, a rapid reconsolidation and intensification of the PNJ; and, 2) Even if a SSW event were to occur, based upon my research, this would likely be an ineffectively propagating SSW event. In other words, the significant warming at the upper levels of the atmosphere will not induce meaningful alterations of the z500 northern annular mode.

What the near miss/borderline displacement will effectuate is a weaker stratospheric vortex, making it more susceptible to future assaults. The evolution of the tropospheric pattern is such that wave-2 should begin to increase by day 10, with potentially a robust spike by 2/10. Given an expected weaker vortex, a potent wave-2 attack could possibly induce a more meaningful stratospheric reversal toward mid February. However, of course, at that point, we are approaching late winter, and the effect of stratospheric warming events tends to be less dramatic. But there are examples in the data w/ analogous background conditions to this year which featured mid/late Feb SSW events. And I currently favor late winter (later in Feb into March) for the best opportunity for a genuine negative AO pattern in the troposphere. However, this is only one possibility. If the wave driving doesn’t progress, we could run the early February regime through March.

Now, what is the early February regime? The MJO aided ephemeral alterations with PNA spike and concomitant downstream trough in the East will rapidly transition into a retracted jet / Aleutian ridge / NW US trough pattern by early February – classic La Nina regime. There will be a transient window 1/28-2/3 for a deep coastal storm on the east coast which could produce snow, when the PNA is conducive. If we do not capitalize on that period, all hope is not lost. I think poleward ridging will develop in the Aleutians given tropical forcing progression and AAM/GWO tendencies. This will force the return of a NW US trough, but if there’s sufficient geopotential height rises extending into the Arctic and/or northeast Greenland from the Scandinavian side, the baroclinic gradient would be sufficiently suppressed to permit a wintry event down to our latitude. If there’s insufficient extension of the poleward ridge, the pattern will be similar to December with February climatology: a snowier pattern for much of New England but not necessarily that good from coastal SNE southward. Overall, Feb 1-15 looks normal to warmer than normal, but not blowtorch. There will be possibilities of snow, but it isn’t a great looking winter pattern. I do believe we will achieve at least one moderate or greater snow event in the 1/28-2/12 period.

Beyond that time, the determinants of a blocky pattern will be contingent upon MJO aid, stratosphere, and other factors. At this point, I would lean toward a continuation of the largely +AO/NAO regime with an initial +PNA transient, leading toward a –EPO/-PNA for most of the first half of February. The weakened state of the stratospheric vortex should permit the neutralization of geopotential heights in the Arctic such that the upcoming few weeks is more favorable than the winter thus far for the possibility of snow. It will favor the Lakes, New England and interior however.

A resurgence of wave-2 in early-mid February could eventually lead to genuine AO/NAO pattern for later Feb-March but that is still highly speculative, and I am not willing to attach significant confidence to the idea just yet.

In sum: it appears to be the type of pattern which will gradually inch us close to my seasonal numbers of 20-26" for NYC. It's not a great pattern for NYC but it could be occasionally "serviceable" with opportunities, given February climatology and sufficient poleward ridging. That's the type of regime which will continue to favor the northern tier / New England. Temperature wise, it looks near normal to above at times at our latitude following the cold shot.

[donsutherland1]

1 hour ago, Isotherm said:

Pattern update:

The anticipated wave-1 increase via the tropospheric precursor pattern and concomitant MJO propagation support has led to an enhanced convergence of energy at the vortex, resulting in sufficient forcing to temporarily displace the stratospheric vortex from the center of the pole. The vortex will be pushed toward Greenland at 50-10hpa by D 10. However, after which, wave-1 convergence begins to decline, and with no follow-up wave-2 assault, and so the resultant outcome may be a near miss; namely, the reduction of zonal winds at 60N/10hpa to weakly positive levels (no reversal). Right now, it appears the wave driving will be sufficient to induce a mean zonal wind reversal at the top of the atmosphere (1hpa), but not further down. Even in the case that zonal winds are temporarily reversed at 10hpa, there are a couple of significant issues: 1) This potential displacement event will likely not be one which results in the subsequent destruction of the vortex, but rather, a rapid reconsolidation and intensification of the PNJ; and, 2) Even if a SSW event were to occur, based upon my research, this would likely be an ineffectively propagating SSW event. In other words, the significant warming at the upper levels of the atmosphere will not induce meaningful alterations of the z500 northern annular mode.

What the near miss/borderline displacement will effectuate is a weaker stratospheric vortex, making it more susceptible to future assaults. The evolution of the tropospheric pattern is such that wave-2 should begin to increase by day 10, with potentially a robust spike by 2/10. Given an expected weaker vortex, a potent wave-2 attack could possibly induce a more meaningful stratospheric reversal toward mid February. However, of course, at that point, we are approaching late winter, and the effect of stratospheric warming events tends to be less dramatic. But there are examples in the data w/ analogous background conditions to this year which featured mid/late Feb SSW events. And I currently favor late winter (later in Feb into March) for the best opportunity for a genuine negative AO pattern in the troposphere. However, this is only one possibility. If the wave driving doesn’t progress, we could run the early February regime through March.

Now, what is the early February regime? The MJO aided ephemeral alterations with PNA spike and concomitant downstream trough in the East will rapidly transition into a retracted jet / Aleutian ridge / NW US trough pattern by early February – classic La Nina regime. There will be a transient window 1/28-2/3 for a deep coastal storm on the east coast which could produce snow, when the PNA is conducive. If we do not capitalize on that period, all hope is not lost. I think poleward ridging will develop in the Aleutians given tropical forcing progression and AAM/GWO tendencies. This will force the return of a NW US trough, but if there’s sufficient geopotential height rises extending into the Arctic and/or northeast Greenland from the Scandinavian side, the baroclinic gradient would be sufficiently suppressed to permit a wintry event down to our latitude. If there’s insufficient extension of the poleward ridge, the pattern will be similar to December with February climatology: a snowier pattern for much of New England but not necessarily that good from coastal SNE southward. Overall, Feb 1-15 looks normal to warmer than normal, but not blowtorch. There will be possibilities of snow, but it isn’t a great looking winter pattern. I do believe we will achieve at least one moderate or greater snow event in the 1/28-2/12 period.

Beyond that time, the determinants of a blocky pattern will be contingent upon MJO aid, stratosphere, and other factors. At this point, I would lean toward a continuation of the largely +AO/NAO regime with an initial +PNA transient, leading toward a –EPO/-PNA for most of the first half of February. The weakened state of the stratospheric vortex should permit the neutralization of geopotential heights in the Arctic such that the upcoming few weeks is more favorable than the winter thus far for the possibility of snow. It will favor the Lakes, New England and interior however.

A resurgence of wave-2 in early-mid February could eventually lead to genuine AO/NAO pattern for later Feb-March but that is still highly speculative, and I am not willing to attach significant confidence to the idea just yet.

In sum: it appears to be the type of pattern which will gradually inch us close to my seasonal numbers of 20-26" for NYC. It's not a great pattern for NYC but it could be occasionally "serviceable" with opportunities, given February climatology and sufficient poleward ridging. That's the type of regime which will continue to favor the northern tier / New England. Temperature wise, it looks near normal to above at times at our latitude following the cold shot.

Great discussion. I agree that an EPO-/PNA-/AO+ pattern increasingly appears likely to dominate during the 2/1-15 period.

[weatherpruf]

4 hours ago, uncle W said:

 

I have a video of that day...my daughter was two at the time...and now shes 29...Time flies...

 

Love those 80's cars! Can't remember it, perhaps it was not a thing over in NJ.

[weatherpruf]

3 hours ago, snowman19 said:

The 1980-1990 winters were extremely hostile to any high latitude blocking, especially Atlantic and arctic blocking. That entire time period was just awful for snow here. It was either cold and dry or warm and raining

Seriously, I only remember 4 events, Jan 82, because of the famous plane crash into the Potomac. the freak April 82 storm, the Feb 83 storm, and the wicked and badly forecast Jan 87 storm. There was nothing significant for several years after that last one. We have since been in a feast or famine cycle it seems.

[snowman19]

3 minutes ago, bluewave said:

Don, this looks like it will be only be the 4th La Nina since 1950 with such a strong Aleutian ridge coupled with a +AO pattern.

The previous 3 winters were 1949-1950, 1971-1972, and the 1988-1989 analog you mentioned.

 

 

 

It's the La Niña combined with the +QBO that supports the poleward Aleutian ridge pattern

[uncle W]

how has the neutral to weak negative winters that followed an el nino working out?...

snowfall...1959-60 had about 6" less in December in every other place but Central Park...

season...Jan 15th...After...total
1959-60......18.6"......20.6"......39.2"
1964-65......10.1"......14.3"......24.4"
1966-67........9.7"......41.8"......51.5"
1978-79........7.5"......21.9"......29.4"
1980-81........9.6"........9.8"......19.4"
1983-84........7.5"......17.9"......25.4"
1992-93........1.9"......22.6"......24.5"
1995-96......39.6"......36.0"......75.6"
2005-06......11.7"......28.3"......40.0"

2016-17......10.1"......

[Paragon]

16 minutes ago, bluewave said:

Don, this looks like it will be only be the 4th La Nina since 1950 with such a strong Aleutian ridge coupled with a +AO pattern.

The previous 3 winters were 1949-1950, 1971-1972, and the 1988-1989 analog you mentioned.

 

 

 

But will this officially even be considered a la nina?  Looking at all the rainfall over California (and now SoCal) it looks like what last year's El Nino was supposed to be delivering for them.

[Paragon]

Just now, uncle W said:

how has the neutral to weak negative winters that followed an el nino working out?...

snowfall

season...Jan 15th...After...total
1959-60......18.6"......20.6"......39.2"
1964-65......10.1"......14.3"......24.4"
1966-67........9.7"......41.8"......51.5"
1978-79........7.5"......21.9"......29.4"
1980-81........9.6"........9.8"......19.4"
1983-84........7.5"......17.9"......25.4"
1992-93........1.9"......22.6"......24.5"
1995-96......39.6"......36.0"......75.6"
2005-06......11.7"......28.3"......40.0"

2016-17......10.1"......

Yes, this is what I've been saying, it's more neutral than anything else.  More research needs to be done into "neutral"- maybe they have their own forcing and that's why we have this pattern.  Look at all the rainfall happening in California, that's more like what last winter was supposed to be out there and not a la nina pattern at all.

[Paragon]

7 minutes ago, uncle W said:

how has the neutral to weak negative winters that followed an el nino working out?...

snowfall

season...Jan 15th...After...total
1959-60......18.6"......20.6"......39.2"
1964-65......10.1"......14.3"......24.4"
1966-67........9.7"......41.8"......51.5"
1978-79........7.5"......21.9"......29.4"
1980-81........9.6"........9.8"......19.4"
1983-84........7.5"......17.9"......25.4"
1992-93........1.9"......22.6"......24.5"
1995-96......39.6"......36.0"......75.6"
2005-06......11.7"......28.3"......40.0"

2016-17......10.1"......

Some nice analogs there- we're actually somewhere in the middle.

Let's use median since the variance is so high that mean doesn't work all that well.

The median prior to Jan 15th is 9.7" and the median after is 21.9"   The median seasonal total is 29.4"

I see why you favor a backloaded snowfall season ;-)

 

[bluewave]

17 minutes ago, snowman19 said:

It's the La Niña combined with the +QBO that supports the poleward Aleutian ridge pattern

The QBO is different now from those previous events.

https://www.esrl.noaa.gov/psd/data/correlation/qbo.data

5 minutes ago, Paragon said:

But will this officially even be considered a la nina?  Looking at all the rainfall over California (and now SoCal) it looks like what last year's El Nino was supposed to be delivering for them.

It's a La Nina with an anomalously wet pattern twist for places like Northern California. The very strong ridge near the Aleutians has displaced the

fire house jet further south. 

[SnowGoose69]

Good news is it is beginning to look like an El Nino next winter.  No idea how strong though, some of the models are going stronger than I thought though.

[Paragon]

11 minutes ago, SnowGoose69 said:

Good news is it is beginning to look like an El Nino next winter.  No idea how strong though, some of the models are going stronger than I thought though.

I heard this last week and it's great news.  Another strong el nino?  Is it unprecedented to have two out of three el ninos be strong?

I like to temper my excitement about ENSO- no matter what that index is, if we don't have some blocking it doesn't matter.  Remember 1994-95 was a moderate el nino ;-)

 

[Isotherm]

Thanks Don. I think we may have a better opportunity rolling the dice with a southwest flow event as geopotential heights decrease in the West and the baroclinic zone lifts northward. The progged orientation of the PNA ridge in the 1/26-2/2 period is not conducive for tucked in coastal storms. We need it more Meridional and less SW-NE oriented, the latter of which tends to suppress / force short waves offshore. I'm not too optimistic about the 1/26-2/1 period. The gradient regime may give us a better shot, but I'm also worried about our area being too far south w/ SE Ridge issues in February.

[Isotherm]

IMO the Aleutian ridging hasn't been particularly impressive / poleward in the means thus far. There have been sufficient low geopotential heights intervals to counteract the signal. True poleward ridging winters should have been colder to date in terms of the temperature departures.