The Sudden Stratospheric Warming 2011/2012

We are currently in the middle of a forecast period with the upper to mid stratosphere undertaking a remarkable warming up when we compare to early winter.

I have to say that I have kept quiet on the model thread recently, as I have found the daily difference of stratospheric modeling inconsistent with being able to give a reasoned tropospheric forecast.

Overall the picture is very promising but when analysing in more detail there are areas of the forecast that could be better - but there is still change for that.

The GFS gives an easier, more straightforward forecast to explain. Here we see the forecast upper warming completely reverse the vortex at the top of the stratosphere (1hPa).



ECM close to agreement here and mean zonal mean wind reversal is forecast on both.



Moving down the stratosphere the forecast displacement seen on the vortex differs. At 10 hPa the ECM suggests that the vortex is trying to reclaim pole position - whereas the GFS is holding the vortex at bay - both suggest further warming





I think the bif=g difference here may be due to different modelling of the E-P flux - suspect that the GFS forecast (if we could see it ) is less equatorwards than the ECM and that could be critical for downwards polar propagation.

As a result the forecast warming at 30 hPa (GFS) looks the most promising that we have seen yet and more central than the ECM.



So looking towards the troposphere, I feel that there is very little to be gained looking further than 6-8 days ahead.

If one scrolls down the folowing link it is possible to see a section of the vortex become sectioned east of Scandinavia and head south before weakening.

http://wekuw.met.fu-...ast=all&lng=eng

It leaves an opening in this process for height rises to develop over Scandinavia from days 6-7 and that is what is being modeled. I suspect how far south this segment of vortex is critical - the further south it reaches the better chance of tropospheric undercutting.

GFS is similar but with differences in keeping a large segment of vortex over the Canadian Arctic. Promising as the weakend vortex has split allowing those rare Svalbard height rises.



I now feel that a great opportunity to get winter started is coming into a closer timeframe and hopefully patience will be rewarded.

c

I expect forecast to be a bit tricky in the 8 to 10 day range as the displacement of the stratospheric vortex might or might not end. Perhaps I can show in charts what I mean about the end of the displacement.

Notice how in this chart the blue low area is centered towards the UK. Now a couple of days later the forecast chart looks like this.

The blue low area is shifting back towards the pole, or perhaps splitting. Not quite sure whether this evolution is right or whether we have a different kind of warming. The following chart suggest perhaps a split at the lowest level.

Notice how the warmer air at the lowest level of the straophere on this chart is making its way round towards the UK from the US. That to me suggests a higher risk of high pressure in the atlantic and towards the UK. The following stratosphere vorticity chart out at tend days suggests a negative AO.


So interpretting this and putting any sort of confidence on things is difficult. Because of the potential transition I would give a low confidence on my thougths which are :
Perhaps ironically the end of the stratospheric warming is giving us a chance of colder weather. Because the colder weather is not really stratospheric warming induced the chance of sustained blocking is limited. My best guess is that we will get a chance at some northerly weather followed by an easterly period. At this point without further changes to the stratosphere I cannot see the cold spell lasting more than a week.
So do we get another warming or not and here I am trending towards saying Yes based on the fact that we should have had some wave breaking over Greenland recently. Charts perhaps give hints but its too early to tell.



Still some variation on Windy and mostly wet will be nice however long it lasts (probably going to regret saying that, I usually do). The old Maxim that whatever the east coast of the US gets, we get soon after might actually hold true for once in the 8 -16 day range, so perhaps worth watching their weather for once. Beyond that I would be guessing, but I think another cold spell in February is likely.




Some feed back on the above post


I just don't trust the ECM 8-10 day forecasts. The T+240 chart, that looks like a scream mask, looks to send the vortex back to a more central position too quickly and I suspect it may be because of the difficulties in modeling a vortex under strain at this point.

Will be interesting to see tomorrows update.



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The heights that we are seeing on the synoptic charts that are building across the Arctic on the eastern side from
the bering sea area are surely a response to the warmings we have and are seeing. I know lower down in the
stratosphere they show up as lower pressure but maybe as they down well from 10 and 30 hpa into the
tropopause they are being displaced further west.


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I suspect that they are - the feedback from before the New Year. It was always going to be a case of when the ball started rolling it would carry on gathering momentum.

Morning all... Just a few thoughts from me on the current situation and unfortunately from my analysis and understanding the outcome is leaning more towards bad news than good news, but it could be somewhere 'down the middle'.

Starting with the following chart however, a piece of good news and of actual observation of the temperature at 30hPa over the N Pole;

http://ds.data.jma.go.jp...RAT/html_e/pole30_n.html

For the first time this winter the temperature has finally risen above the climate average and clealry when compared with late December and the majority of early January it is clearly quite a rise in temperature, but still nothing really 'major'. Clearly what has to be acknowledged here is that some 'factor' has caused this warming and clearly that has been discussed in depth in recent days and weeks and clearly that is primarily down to discussed warming within the stratosphere that has taken place over the last 7 to 14 days. So the current state of affairs is that compared with December the strat is warmer, not majorly so, but it is clearly warmer and without question that has and is having an affect on the PV compared with conditions evident through December and also into early January.

Now some general analysis and overall I'm not seeing a huge amount of positives at the moment. Clearly the other thing to note is that like any forecast, the information below is subject to change, to either a better scenario or worse etc.

http://wekuw.met.fu-berl...forecast=all&lng=eng

If you follow through the series of charts on that linke, despite evident warming at the 10hPa the main vortex becomes relocated over the polar region once again now by day 9 and day 10, with the centre almost directly over the N Pole at the 240hr, not an ideal situation.

http://wekuw.met.fu-berl...ll&var=u&lng=eng

The zonal wind, whilst reversing and becoming negative near day 3 and day 4, by the latter half of the forecast period actually goes back the other way now, particularly above 10hPa and near 60N to 70N, signal a renewed threat that perhaps the zonal wind will strengthen.

http://wekuw.met.fu-berl...ar=ta1&lng=eng#fig11

Wave 1 temperature prediction is also on the wane as well towards the back end of the forecast period, further negative signs.

http://wekuw.met.fu-berl...&alert=1&lng=eng


The above link does highlight things very well also. Notice that whilst the 1hPa ZW is near 0, the more important 10hPa and 30hPa values are forecast to rise towards the middle and latter half of January. Clearly they are lower than throughout December, but there is no sign of any reversal of any kind. The other important factor as well is that the EPV (bottom image) is poor, the EP vectors a forecast to drop away now and no only that there is little sign for any poleward direction to the EP flux and they continue to be on an angle.

http://wekuw.met.fu-berl...&alert=1&lng=eng

In according with the the Wave 1 temp prediction above you can see on the above imagery as well, that Wave 1 in particularly is forecast to decline through the forecast period as well. In sort of comparison mind, the GFS in particular looks very promising in terms of temperature rises over the polar at the 10hPa level at 240hr;

http://www.cpc.ncep.noaa...iles/gfs_t10_nh_f240.gif

So in my opinion the the latest forecast data isn't as promising as to was say 5 to 7 days ago. There have been factors involved which have helped to destabilise the PV compared to what it was like in December, that goes without question, but equally the latest forecast data does seem to suggest a less than favourable environment to really disrupt the PV within the medium to long term.

Clearly forecast data can and does change, but those hoping for a significant SWW event within the near future will likely be dissapointed as I can't see it happenning.

Matt.


Matthew Hugo BSc(Hons), FRMetS
Meteorologist
Weather Commerce Ltd
On Twitter @MattHugo81

Today's update in full.

So far this winter we have seen an extremely cold stratosphere dominate proceedings. This has led to a protracted period of zonality caused by the vortex intensification that resulted from the cold.

Around Christmas time we had the first signs that things would change and sure enough just under a month later the changes are working there way through to the tropospheric output. These changes resulted from a series of remote wave breaking events at the top of the stratosphere introducing warmer air that has taken time as it has propagated nodally down the stratosphere.

We are now at a situation where currently we are seeing a warming into the core of the vortex far closer to the troposphere than encountered so far this winter - at the 30 hPa level.

The upper warnings so far have had the net effect of dragging the mean zonal negative winds equator wards which has somewhat inhibited the effect felt in northern latitudes tropospherically with the stratospheric polar vortex reducing but still present.



However this could change with the positioning of the next warming at 30 hPa:



And we are likely to see a far greater lower negative anomaly of mean zonal winds by the end of the month:



So we can compare the forecast for the mean zonal winds and look to see that the polar vortex has reduced dramatically in intensity as we are not too far away from a technical SSW.



So what does this mean for us on the ground?

Well to get a better idea we need to be looking at the charts for the lowest part of the stratosphere at around 100 hPa

Both the GFS and ECM are modelling a weaker less stable vortex that is constantly on the shift. In fact there has been some suggestions of splitting by day 10





If this occurs then any Siberian vortex could exert some pressure on the Siberian High pushing the Russian high further west towards the UK followed by a Greenland pressure rise after that. This also fits in nicely with the GWO rather than working against this.

The troposphere models are coming up with these scenarios. Finally, the slow drip feed of the stratospheric change into the troposphere is coming close to bearing fruit.

c

Latest Update.

We still have encouraging signs filtering down from the stratosphere both for the short term and longer term outlooks.

Let's start long term. It looks like the upper strat forecasts are indicating another round of warming in around 10 days time. This is supported by both the GFS and ECM. Remember that the stratosphere hash't regained it's former strength yet so theoretically we shouldn't need as strong a warming to tip the scales this time.





This seems to be initiated by an increase in wave number two activity - the vortex splitting wave , perhaps being set off by an expected strong mountain torque. This will be useful further down the line - if the cold spell kicks off, a split could aid in prolonging this type of scenario. We see a split being forecast by the GFS at T+240 and 30 hPa.



So, carrying on we need to look at the shorter term.

The possibility of a Scandi block is well supported by the lower stratospheric charts. The only uncertainty remains in how much energy can get under the block to keep it sustained for the long term.

At T+168 the 100 hPa chart is very favourable for there being enough energy.



The T+240 has changed a lot since yesterdays run so we will need to wait until tomorrow for that.


The GFS 10 Day chart suggests a healthy Svalbard block and is trending towards a major split confirmed by the earlier 30 hPa chart.



Even if the easterly doesn't hit big time I suspect a below average February will be on the cards - maybe even significantly so!

Just been having a through look at the stratospheric charts to see if we can get an idea of where we are heading.

Firstly it should be stressed that the polar vortex is very much weakened since the recent warming back in January and that this state is likely to persist through February. We are already seeing high latitude blocking through the extension of the Siberian high, and the continued weakened state of the stratosphere is likely to persist and lead to further HLB's developing over the northern hemisphere.

Those who continually suggest that we are about to see a return to the increased strength of polar vortex witnessed during December are likely to be not looking at the bigger picture. The odd run may suggest more zonal conditions but these are unlikely to verify. Do look at NH charts and don't rely on Atlantic segmented charts.

So, looking at day five we can see when looking at the 100hPa charts why the Atlantic is pushing the block back west. Both the GFS and ECM suggest a trough extending into the north of Greenland temporarily dropping heights to our northwest.





It is from this point on that divergence emerges in the stratospheric profile and this is influencing tropospheric output.

After this point the polar vortex is likely to split due to increased wave number 1 and 2 activity. How this split is modeled will depend on where the remaining segments of polar vortex and increased potential vorticity occur. And also where HLB's are likely to occur.

The split looks likely to occur around the Alaskan region from around day 8. The GFS goes for a straightforward split from Alaska to Siberia leaving an elongated lobe of vortex over Greenland and a likely flatter jet stream over the Atlantic.



This is not what we would like to see!

The ECM solution is more complex, with the Greenland vortex section splitting over Greenland and the Azores high attempting to link up with the Alaskan high.



This is far the more favourable option.

Higher up the stratosphere the increased wave activity is likely to lead to further vortex disturbances. The forecast vortex strength at 30hPa is less than 5m/s and this fits in well with another downwelling of negative mean zonal winds that has just restarted.





Even if the GFS solution is correct I would still think that further along the line that the positioning of the vortex lobes will change, and I would far rather see a very disturbed polar vortex than the extremely strong one that we saw due to the cold stratospheric start to winter.