Winter 2014-2015 Medium-Term Discussion

[mrgolf]

I also wanted to add that at what point this winter can we give up on a SSW event not happening? Do we want to see the qbo rise from its current position to feel confident in one occurring before winter is over? I apologize for all the questions but I think a SSW would be a game changer for us

[GaWx]

Here is the latest daily update (as of day 363):http://www.cpc.ncep.noaa.gov/products/stratosphere/strat-trop/gif_files/time_pres_TEMP_ANOM_OND_NH_2014.gif

Though continuing to warm, this is not warming as fast as that prog from Saturday had suggested. To get a strong SSW, it usually needs to be faster than this (say, ~4 C/day). The warmest anomaly warmed only from ~+12-13 C yesterday to ~+14 C today, only ~1.5 C rise (though absolutes would be warming more due to the rather significant rise in normals in very late December). This not so fast rise tells me that it may not get close to the brown/+28+ threshold that would make it a top 12 SSW per that criterion. However, there's still time, especially if the warming accelerates over the next couple of days. I think that the earliest it would max out would be the map two days from now (for 12/31) and some progs suggest it may not max out for at least a few days after that.

This current warming is not going to allow it to get anywhere close to the brown color (+28+) per the brand new update. This shows at least a temporary anomaly maxing out only near +14 C, which suggests that that prog from Saturday was way overblown. Unless there is a sudden strong rewarming very soon (some runs didn't have a max for several more days) this SW is done, nowhere near a major SSW, and is a big disappointment to me vs my expectations based on Saturday's progs, which had shown (as posted here) a whopping 37C absolute warming (and ~31C anomaly warming) at 5 mb by today's update vs what actually looks like only about a 20ish absolute warming so far!

http://www.cpc.ncep.noaa.gov/products/stratosphere/strat-trop/gif_files/time_pres_TEMP_ANOM_OND_NH_2014.gif

[donsutherland1]

Currently, the Arctic Oscillation (AO) is +2.619. The ensemble forecasts continue to indicate that the AO could reach or exceed +3 during the 1/1-10 timeframe. Typically, that is a signal for below normal snowfall in parts of the eastern U.S., especially after low snowfall in December.

 

For illustrative purposes, the following charts show the latest ensemble forecasts and January snowfall outcomes for Boston.

 

 

Needless to say, there can be exceptions. One such exception, which featured a remarkable turnaround from a strongly positive AO to a persistently negative one was 2005. 2005 saw 43.3" snow fall at Boston. However, December 2004 saw 7.2" snow fall at Boston. December 2014 registered just 0.3".

 

For now, a severely negative EPO has delivered a lot of cold to North America.

[Weathergun]

This current warming is not going to allow it to get anywhere close to the brown color (+28+) per the brand new update. This shows at least a temporary anomaly maxing out only near +14 C, which suggests that that prog from Saturday was way overblown. Unless there is a sudden strong rewarming very soon (some runs didn't have a max for several more days) this SW is done, nowhere near a major SSW, and is a big disappointment to me vs my expectations based on Saturday's progs, which had shown (as posted here) a whopping 37C absolute warming (and ~31C anomaly warming) at 5 mb by today's update vs what actually looks like only about a 20ish absolute warming so far!

http://www.cpc.ncep.noaa.gov/products/stratosphere/strat-trop/gif_files/time_pres_TEMP_ANOM_OND_NH_2014.gif

 

Heat/momentum flux has peaked with wave 1. Flux and temps may rise again with wave 2 in a few days. But models show 10hpa vortex consolidating again over north pole in the 7-10 day period. So this is probably not major event and will likely not result in large -AO through mid-January. The strong -QBO at 30mb and geomagnetic activity from the sun appears to be playing role quick recovery of polar vortex. Wave-breaking activity is reduced.

 

 

[Absolute Humidity]

Heat/momentum flux has peaked with wave 1. Flux and temps may rise again with wave 2 in a few days. But models show 10hpa vortex consolidating again over north pole in the 7-10 day period. So this is probably not major event and will likely not result in large -AO through mid-January. The strong -QBO at 30mb and geomagnetic activity from the sun appears to be playing role quick recovery of polar vortex. Wave-breaking activity is reduced.

 

 

Prob doesn't mean much but all is quiet now.

[donsutherland1]

Morning thoughts...

 

1. The AO has now reached +3.096. An AO that reaches or exceeds +3 during the first 10 days of January has often occurred in winters with below normal January snowfall in the Middle Atlantic and southern New England regions. Winter 2004-05 was a notable exception, as the AO went strongly negative after mid-month.

 

2. The guidance is now more strongly indicating that the EPO will go positive toward mid-month. The PNA is forecast to go positive by that time, as well.

 

3. The sensible weather impact will likely be a colder than normal first 10-12 days of January (with some exceptions) across much of the CONUS and Canada, especially as Arctic air will be involved for a time. The western third of the CONUS will probably wind up warmer than normal. Moderation might begin to develop as the calendar approaches mid-month if the AO remains positive.

 

4. Since November 1, the longest EPO+ duration was 10 days. If the return of the EPO- occurs as it has since then, the EPO- period could be temporary.

[Chinook]

Talking about a positive AO, how about a positive NAO. The SLP in Portugal could be 1046mb while the SLP in Iceland could be 946mb next week. (18z GFS)

[donsutherland1]

Talking about a positive AO, how about a positive NAO. The SLP in Portugal could be 1046mb while the SLP in Iceland could be 946mb next week. (18z GFS)

It will be interesting to see if this verifies. If so, perhaps the NAO will reach +2 for the first time since April 23, 2013.

[Absolute Humidity]

Morning thoughts...

 

1. The AO has now reached +3.096. An AO that reaches or exceeds +3 during the first 10 days of January has often occurred in winters with below normal January snowfall in the Middle Atlantic and southern New England regions. Winter 2004-05 was a notable exception, as the AO went strongly negative after mid-month.

 

2. The guidance is now more strongly indicating that the EPO will go positive toward mid-month. The PNA is forecast to go positive by that time, as well.

 

3. The sensible weather impact will likely be a colder than normal first 10-12 days of January (with some exceptions) across much of the CONUS and Canada, especially as Arctic air will be involved for a time. The western third of the CONUS will probably wind up warmer than normal. Moderation might begin to develop as the calendar approaches mid-month if the AO remains positive.

 

4. Since November 1, the longest EPO+ duration was 10 days. If the return of the EPO- occurs as it has since then, the EPO- period could be temporary.

A bit of AO reversal starting to show up near mid month. This would support Cohen's thoughts of AO flipping to negative after this well predicted positive period.

[donsutherland1]

A bit of AO reversal starting to show up near mid month. This would support Cohen's thoughts of AO flipping to negative after this well predicted positive period.

Hopefully, but a measure of caution is needed, especially given how difficult it has been to sustain blocking so far.

 

There have been other January cases where the AO plunged 3 or more standard deviations from a reading of +3 or above over a 5-day period that saw the blocking fail to take hold. Some examples include January 1976, January 1984, January 1992, and January 1993. Some cases saw blocking take hold or become predominant. Those cases are January 2005 and January 2006.

[mrgolf]

Don....happy new year!! This winter hasn't gone to plan like a lot of forecasters envisioned. I know the ao and nao haven't helped, but what's causing them to stay so positive and what's likelihood of them trending negative later? Basically, do we need a SSW event to materialize fairly soon and qbo weaken before we run out of time? Thanks

[donsutherland1]

Don....happy new year!! This winter hasn't gone to plan like a lot of forecasters envisioned. I know the ao and nao haven't helped, but what's causing them to stay so positive and what's likelihood of them trending negative later? Basically, do we need a SSW event to materialize fairly soon and qbo weaken before we run out of time? Thanks

SSW events can help. But sometimes such events occur after a period of intense blocking, so blocking is not dependent on the occurrence of SSW events. A lot is still not sufficiently understood about the AO. Its seasonal predictability may not be as good as the initial promise for the SAI had indicated. Time will tell on that matter.

[Isotherm]

The tropospheric AO regime should begin to turn increasingly negative post January 15th, and particularly by the 20th / thereafter. I believe this will occur b/c of a variety of forcing mechanisms, stratospheric trends inclusive.

 

Keep in mind, a stratospheric warming event does not need to be classified as "major" to have impacts in the troposphere. The current situation is in fact a sudden stratospheric warming event of at least moderate magnitude. The development of a warm / very warm stratosphere substantially increases the probability for the persistence and / or initiation of a more perturbed tropospheric vortex. This is evidenced by the fact that the vast majority of winters in which the precursor stratosphere pattern was warm / perturbed led to increased propensity for negative AO conditions in the ensuing winter.

 

Poleward heat flux is now reaching daily maximum levels of approximately 25-26 K m/s, quite analogous to the early 2004 heat flux as depicted below:

 

Current:

 

 

 

2004:

 

 

 

 

The 2004 SSW event peaked at slightly warmer than -55C for the 90 to 65N region at 70mb:

 

 

 

Currently we continue to warm rapidly at 70mb, and based upon forecasts, I think we warm a bit more over the next couple days w/ a peak at approximately -58C or so.

 

 

 

 

Tropical forcing, while on the weaker side, is becoming rapidly more favorable for the development of a classic Nino regime in the medium term w/ increased PNA ridging / Aleutian troughing. For the first time this autumn and cold season, we should see more sustained favorable forcing. The control run of the ECMWF is just beginning to detect the possibility for negative AO onset in the 15th-20th period. Any negative NAO development would probably wait until after the 20th.

 

Take this with a grain of salt, though I believe it has decent accuracy and support from other signalling: The long-term tropical forcing based geopotential height forecast suggests a strong negative NAO / Greenland blocking signature in early February.

[GaWx]

Isotherm,
Very interesting post. So, in summary, are you saying that the suddenness of strat warming isn't nearly as importance as the overall level and persistence of warming? If that's the case, then the importance of actual SSW events, even major ones, has probably been exaggerated to a degree. After all, isn't there cooling behind SSW's, regardless?
Anyway, I have noticed that the AO sometimes doesn't drop later even if there is a SSW. Maybe your reasoning is the answer to why that is the case?
Have you done a study of how the overall strat temp. has or has not correlated well with a -AO year by year?

Edited several times

[winterymix]

...A lot is still not sufficiently understood about the AO...

Don:  my hunch is that this seasonal pattern in the East of warm + wet vs. cold + dry has a reasonable probability of persisting.  The ENSO pattern is forecast (by ensemble) to be quite stable and seems devoid of volatility.

 

 

Furthermore, the MJO oscillation is trending towards phases 5 through 8 which may be favorable for winter weather in the East.  However, consideration of the vapid strength of the signal is a concern.

 

 

The flies in the ointment are potential unforeseeable surprises.  The winter of late 1982 into early 1983 was warm but with a single blockbuster KU storm.

 

On a tangential note, are there any inferences we can draw about equatorial Western Pacific tropical forcing near Indonesia?  The AirAsia crash was likely affected by tropical convection.  This pattern has persistence as the salvage crews struggle to catch a break in the stormy pattern.

[GaWx]

Don:  my hunch is that this seasonal pattern in the East of warm + wet vs. cold + dry has a reasonable probability of persisting.  The ENSO pattern is forecast (by ensemble) to be quite stable and seems devoid of volatility.

 

Furthermore, the MJO oscillation is trending towards phases 5 through 8 which may be favorable for winter weather in the East.  However, consideration of the vapid strength of the signal is a concern.

 

statphase_full.gif

 

The fly in the ointment are unforeseeable surprises.  The winter of 1983 was warm but with a single blockbuster KU storm.

 

 The interesting thing I've learned over the last week through my own analysis of January daily Atlanta temperature data since 1975 is that a weak MJO going through the outer half of the COD or barely outside the COD through phases 6-7-8-1-2-3 (especially 7-8) has been on average the coldest for Atlanta (and supposedly for at least the bulk of the SE US and probably much of the East) in January as opposed to a strong MJO going through those same phases.

 I don't know why that has been the case. This is based on a very large sample of days: 1,240 of them to be exact. Anyone have any ideas as to why that would be the case?

 

 Also, does anyone know why the GFS/GEFS MJO forecasts haven't updated over the last few days? Those maps are blank although the EPS/Euro/JMA/UKMET have updated as of yesterday. Also, I find it very strange that both the Euro and the JMA initialized the MJO in the COD phase 6 whereas it is supposedly around a 1.5 amplitude in phase 5. What gives?

 

GEFS forecast: not there for last few days

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/ncpe.shtml

 

 

EPS forecast: initialized yesterday in COD

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/ECMF_phase_MANOM_51m_full.gif

 

JMA forecast: initialized yesterday in COD

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/jman.shtml

 

But we're not in the COD and in a moderate phase 5 if you believe this:

http://www.bom.gov.au/climate/mjo/graphics/rmm.phase.Last40days.gif.small.gif

 

**Edited several times**

[Isotherm]

Isotherm,

Very interesting post. So, in summary, are you saying that the suddenness of strat warming isn't nearly as importance as the overall level and persistence of warming? If that's the case, then the importance of actual SSW events, even major ones, has probably been exaggerated to a degree. After all, isn't there cooling behind SSW's, regardless?

Anyway, I have noticed that the AO sometimes doesn't drop later even if there is a SSW. Maybe your reasoning is the answer to why that is the case?

Have you done a study of how the overall strat temp. has or has not correlated well with a -AO year by year?

Edited several times

 

 

Larry -- I have. Using the data since 1979, I've found an R value of 0.71 as far as the correlation between warmer (cooler) than normal stratospheric temperatures at the 70mb level and positive (negative) AO mean conditions in the troposphere. There are plenty of cases with an apparent disconnect, but overall, there is a strong tendency for increased tropospheric blocking when the stratosphere is perturbed / warmer than normal. The atmosphere doesn't know whether or not we've reached an artificial classification, though certainly the greater the magnitude of the warming event, the higher the probability of downwelling into the troposphere. However, there is a strong propensity for cool stratosphere / +AO and warm stratosphere / -AO conditions. Thus, the strong warming at all levels of the stratosphere coupled with improving trends in tropical forcing (thereby inducing a more Nino-like Pacific H5 configuration) lead me to believe that the totality of forcing mechanisms should tilt the AO negative in the second half of January. I have less confidence in the NAO state.

[winterymix]

Heather Archambault came up with a wonderful idea.

 

I think it is going to come down to this:

 

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CDMQFjAC&url=http%3A%2F%2Fcstar.cestm.albany.edu%2FCAP_Projects%2FProject2%2FCool-Season_Regime%2FH.Archambault%2520Thesis%2520Presentation_042205.ppt&ei=zKmpVIjmCILhggS6-4PQDA&usg=AFQjCNH39l2ZaiF-HK41iGbfDRS3zINflA&sig2=3sb3Og1gs-xAObL0-m-FTQ&bvm=bv.82001339,d.eXY

 

The overall signal if for persistence.

However, if we get at particular phase shift where the MJO, AO and NAO all coincide, we can get a KU snow.    A great many "ifs".

 The interesting thing I've learned over the last week through my own analysis of January daily Atlanta temperature data since 1975 is that a weak MJO going through the outer half of the COD or barely outside the COD through phases 6-7-8-1-2-3 (especially 7-8) has been on average the coldest for Atlanta (and supposedly for at least the bulk of the SE US and probably much of the East) in January as opposed to a strong MJO going through those same phases.

 I don't know why that has been the case....

Larry -- I have. Using the data since 1979, I've found an R value of 0.71 as far as the correlation between warmer (cooler) than normal stratospheric temperatures at the 70mb level and positive (negative) AO mean conditions in the troposphere. There are plenty of cases with an apparent disconnect, but overall, there is a strong tendency for increased tropospheric blocking when the stratosphere is perturbed / warmer than normal....

[donsutherland1]

Don:  my hunch is that this seasonal pattern in the East of warm + wet vs. cold + dry has a reasonable probability of persisting.  The ENSO pattern is forecast (by ensemble) to be quite stable and seems devoid of volatility.

 

sstsa.gif

 

Furthermore, the MJO oscillation is trending towards phases 5 through 8 which may be favorable for winter weather in the East.  However, consideration of the vapid strength of the signal is a concern.

 

statphase_full.gif

 

The fly in the ointment are unforeseeable surprises.  The winter of late 1982 into early1983 was warm but with a single blockbuster KU storm.

 

On a tangential note, are there any inferences we can draw about equatorial Western Pacific tropical forcing near Indonesia?  The AirAsia crash was likely affected by tropical convection.  This pattern has persistence as the salvage crews struggle to catch a break in the stormy pattern.

I believe there is real risk of such an outcome. Certainly, for January odds likely favor below normal snowfall in the Middle Atlantic region. That has often been the case when the AO reached +3 or above during the first 10 days of January. AO- has been present at the start of 92% of January KU-type snowstorms, as well. Of course, January 2005 was an exception and the ENSO conditions are currently remarkably similar to those of 2005. How the MJO progresses may determine whether a snowier end to the month can occur.

[scottmartin49]

Heather Archambault came up with a wonderful idea.

 

I think it is going to come down to this:

 

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CDMQFjAC&url=http%3A%2F%2Fcstar.cestm.albany.edu%2FCAP_Projects%2FProject2%2FCool-Season_Regime%2FH.Archambault%2520Thesis%2520Presentation_042205.ppt&ei=zKmpVIjmCILhggS6-4PQDA&usg=AFQjCNH39l2ZaiF-HK41iGbfDRS3zINflA&sig2=3sb3Og1gs-xAObL0-m-FTQ&bvm=bv.82001339,d.eXY

 

The overall signal if for persistence.

However, if we get at particular phase shift where the MJO, AO and NAO all coincide, we can get a KU snow.    A great many "ifs".

Nice work. Crosstab that to AO and type of precip during winter and we'd have something to work with if the sample was large enough! 

[donsutherland1]

Brief morning update...

 

1. ENSO conditions remain remarkably similar to those at a similar point in time during winter 2004-05.

2. Some GFS ensemble members are suggesting a large decline in the AO similar to what happened in January 2005.

3. Both the Day 8 and Day 11 GFS ensemble analogs have a date from January 2005.

[LakeEffectOH]

QBO index for Dec. just in...

 

Dec. QBO at 30mb was a record -25.35.  The Nov. QBO was -23.65.

[Big O]

QBO index for Dec. just in...

 

Dec. QBO at 30mb was a record -25.35.  The Nov. QBO was -23.65.

 

Would this support more blocking (i.e., -AO and -NAO)?

[LakeEffectOH]

Would this support more blocking (i.e., -AO and -NAO)?

A negative QBO often supports more blocking, but a very negative QBO can possibly do the opposite by strengthening the polar vortex.  The winter of 2005-2006 (esp. Jan '06) is a good example.  The QBO so far this winter is similar to that of 2005-2006.

[Isotherm]

A negative QBO often supports more blocking, but a very negative QBO can possibly do the opposite by strengthening the polar vortex.  The winter of 2005-2006 (esp. Jan '06) is a good example.  The QBO so far this winter is similar to that of 2005-2006.

 

 

 

I've yet to read any literature on the detrimental effects of a strongly negative QBO insofar as it decreases the probability of a negative northern annular mode.  No one seems to have a paper on it. 2005-06 had a -28, -29, -29.5, -25 QBO for Sept / Oct / Nov / Dec respectively and the AO state was strongly negative for December, and still slightly negative Jan-Feb. What would be the physical reasoning for a very negative QBO precluding the initiation of blocking and/or limiting tropospheric vortex perturbation?

[LakeEffectOH]

I've yet to read any literature on the detrimental effects of a strongly negative QBO insofar as it decreases the probability of a negative northern annular mode.  No one seems to have a paper on it. 2005-06 had a -28, -29, -29.5, -25 QBO for Sept / Oct / Nov / Dec respectively and the AO state was strongly negative for December, and still slightly negative Jan-Feb. What would be the physical reasoning for a very negative QBO precluding the initiation of blocking and/or limiting tropospheric vortex perturbation?

It would be interesting to find out about what effect (if any) a strongly negative QBO has on the polar vortex.  I have only heard a couple of mets say that a strong - QBO is not conducive to blocking.

[Weathergun]

I've yet to read any literature on the detrimental effects of a strongly negative QBO insofar as it decreases the probability of a negative northern annular mode.  No one seems to have a paper on it. 2005-06 had a -28, -29, -29.5, -25 QBO for Sept / Oct / Nov / Dec respectively and the AO state was strongly negative for December, and still slightly negative Jan-Feb. What would be the physical reasoning for a very negative QBO precluding the initiation of blocking and/or limiting tropospheric vortex perturbation?

 

Some differences between that year and this one that we saw the -QBO descend more at 50mb early in fall 2005. When it descends we tend to see easterly QBO winds weaken at 30mb too. Geomagnetic activity has also been higher this winter. Both factors likely contributing to slower breakdown stratospheric vortex and development of high-latitude blocking this year.The good news is that is the -QBO has started to descend more the last two months. Hopefully the sun will calm down as well:

Sept/Oct/Nov/Dec 2005 QBO at 50mb:

-10.20 -11.39 -12.29 -12.18 -12.42

 Sept/Oct/Nov/Dec 2014 QBO at 50mb:

-0.15  -1.03  -2.32  -5.24  -8.61

 

Jan 1-5 2006 KP-Index

 

 

Jan 1-5 2015 KP-Index

 

[Isotherm]

10mb temperatures have now surged up to near record levels at about -40C, and 100mb poleward heat flux as exceeded the previous daily maximum at approximately 28 K m/s. Both occurrences tend to be precursors to tropospheric perturbation, particularly if we get another spike, which seems possible based upon current data.

 

 

 

 

 

 

A comparison to 2004 shows we had a double spike around -40c at 10mb. Poleward heat flux was actually slightly weaker.

 

 

 

 

[NJwinter23]

10mb temperatures have now surged up to near record levels at about -40C, and 100mb poleward heat flux as exceeded the previous daily maximum at approximately 28 K m/s. Both occurrences tend to be precursors to tropospheric perturbation, particularly if we get another spike, which seems possible based upon current data.

 

 

 

 

 

 

A comparison to 2004 shows we had a double spike around -40c at 10mb. Poleward heat flux was actually slightly weaker.

 

 

 

 

 

Hey Isotherm,

 

I wouldnt consider this particular warming event as a precursor to tropospheric blocking. Rather, it was primarily the tropospheric pattern that has been a precursor to the warming event, causing the vortex split from the bottom on up to 10mb peaking this week (it wasnt technically a ssw as you know)...The vortex  is actually going to gather itself back together after this week and will need another shot to hopefully get our ssw in the coming weeks.

[Isotherm]

Hey Isotherm,

 

I wouldnt consider this particular warming event as a precursor to tropospheric blocking. Rather, it was primarily the tropospheric pattern that has been a precursor to the warming event, causing the vortex split from the bottom on up to 10mb peaking this week (it wasnt technically a ssw as you know)...The vortex  is actually going to gather itself back together after this week and will need another shot to hopefully get our ssw in the coming weeks.

 

 

NJwinter -- I agree with the bolded, namely that this was a bottom-up event induced by strong tropospheric wave driving. I think we might be talking semantics as far as the stratospheric warming, but the current event is a minor to moderate warming as westerly winds slowed significantly for a few days in conjunction w/ rapid warming. But yes, we haven't had a major SSW yet which involves the complete reversal of 60N/10mb winds to easterly for 5 consecutive days or more. It appears we cool down over the next several days and attempt another wave 2 / vortex split in mid January. Remains to be seen if that one is major. However, from what I've researched, even minor to moderate stratospheric warming events substantially heighten the probability for the development of a more perturbed tropospheric polar vortex. Should be interesting to see how this month plays out.