Stratosphere Temperature Watch

[kold weather]

I agree that a +ve AO signal seems to be more likely and the GFS ensembles does seem to be quite keen on bringing this in by day 10.

What could happen is what we see on the 12z GFS op run, where the jet stays far enough south and we see the so called sausage high which is a weak area of relative higher heights and the jet stays to the south...way too soon for that sort of call and indeed I've seen models not latch onto those till 96-120hrs out...Feb 07 is a great example of that.

[brogdale]

I would agree with that cc. Sometimes it is difficult to explain stratospheric processes in a clear and coherent manner. Keep your posts coming - you seem to have a clear idea of the synoptics - makes me think that you have been posting somewhere else previously!

Good post Brogdale. It is always difficult picking through these type of papers to get to the bare bones.

I am not as convinced as I was a couple of days ago that the current increased forecast wave 2 activity is going to lead to anything. Hopefully it will, but I am beginning to see signs in the forecasts that the stratospheric vortex is regrouping and regaining strength. Both the ECM and GFS suggest this with no significant warming on the horizon. However we still have a significantly cold tropical stratosphere which in theory should have an limiting effect on the strength of the vortex. In fact, when we look at the tropical stratosphere 30 hPa readings we see that the low temperatures are records for this time of year since the recordings began.

Looking from a stratospheric point of view at the possible breakdown of northern (Greenland) blocking I believe that we are still at least 10 days away judging by the GFS 100 hPa forecasts. At day 10 the vortex is reforming, but still showing signs of a declining Greenland high that may move westwards, with a Scandinavian trough and the UK in a probable northerly airflow.

The blocking forecast still looks good at this timeframe and supports this.

c

Hi Chionomaniac

I agree that any 'key day' is going to be some way off, but i do sense that we might be embarking on a 'growing stage' for another SSW.

Based on the paper I posted above, there are signs to indicate that any SSW that did develop over the next few weeks might well be a downward propagator.

This forecast:-

does appear to show the 'pre-conditioned' +ive zonal anomalies (50 - 80N) in the strat that preceed day -5 in a propagator There also appears to be good indications of another pre-condition for propogation; negative zonal anomalies in the upper trop.

Taken with the Wave 2 increases I thought it looks to be a situation of some hope?

[cooling climate]

Here we go again ties in with the zonal wind anomaly charts.

Hi Chionomaniac what a winter this is shaping up to be.

As far as posting goes...mainly on the Netweather site,occasionally on solar 24

and The weather outlook(two).

Excellent thread by the way.

[chionomaniac]

One can see the great negative zonal mean anomalies forecast the coming days. These are responsible for the easterly winds seen at our latitude and the northern blocking.

They look more favourable than those seen after the SSW last winter due to the split vortex originating lower down.

http://www.cpc.ncep.noaa.gov/products/stratosphere/strat-trop/gif_files/time_pres_UGRD_ANOM_ALL_NH_2009.gif

Still no sign of a SSW this winter though the 10 and 30 hPa levels are forecast to warm over the next few days.

[Methuselah]

The way things are going so-far, we mightn't need a SSW???

[chionomaniac]

The way things are going so-far, we mightn't need a SSW???

Indeed Pete, the very favourable November stratospheric conditions have set us up nicely for the start of winter.

[Mark Bayley]

I've noticed that the the stratospheric temps are predicted to go back down to below average with no warming currently predicted for some while, would this mean that the polar vortex will regain strength with the AO trending positive? Or are we expecting a warming around the end of December which should help deliver much colder weather in the second half of Jan, or before depending on how long it takes the effects to be felt?

[SteveB]

I've noticed that the the stratospheric temps are predicted to go back down to below average with no warming currently predicted for some while, would this mean that the polar vortex will regain strength with the AO trending positive? Or are we expecting a warming around the end of December which should help deliver much colder weather in the second half of Jan, or before depending on how long it takes the effects to be felt?

I know we are in a cold spell at the moment, but I can't help but take an interest in possible future cold spells in Jan/Feb.

Any thoughts from GP or Chio?.

[BrickFielder]

The currently split vortex looks like joining up again in about 3 days.

This means that most forecast beyond 3 days will have a lot of uncertainty in them. I specifically don't like the way the vortex forms up into the traditional vortex pattern and think the historical pattern bias may be a little too strong for this scenario.

Current potential vorticity charts show high pressure to our north.

Five days forward and we have a very different picture.

Before the cahnge comes through models are suggesting a northerly for the weekend with flows favourable for polar low formation to the south of iceland.

Looking at the stratospheric forecasts I have some severe doubts about the northerly happening in the way the models depict.

Thinking about triggers for vortex splits it looks like last februaries vortex split was triggers by a zonal wave two pattern.

Our current split however seems to have been triggered by zonal wave 1 which under normal circumstances would just push the vortex away from the pole rather than split it. I guess the weak vortex allowed the split, but typically this type of anomaly (stratospheric warming) does not last long.

For a longer peiod of cooler weather (two weeks +) we could really do with a zonal wave 2 anomaly right about now for colder weather in January. Surprise suprise right on cue.

[phil nw.]

The currently split vortex looks like joining up again in about 3 days.

This means that most forecast beyond 3 days will have a lot of uncertainty in them. I specifically don't like the way the vortex forms up into the traditional vortex pattern and think the historical pattern bias may be a little too strong for this scenario.

Current potential vorticity charts show high pressure to our north.

Five days forward and we have a very different picture.

Before the cahnge comes through models are suggesting a northerly for the weekend with flows favourable for polar low formation to the south of iceland.

Looking at the stratospheric forecasts I have some severe doubts about the northerly happening in the way the models depict.

Thinking about triggers for vortex splits it looks like last februaries vortex split was triggers by a zonal wave two pattern.

Our current split however seems to have been triggered by zonal wave 1 which under normal circumstances would just push the vortex away from the pole rather than split it. I guess the weak vortex allowed the split, but typically this type of anomaly (stratospheric warming) does not last long.

For a longer peiod of cooler weather (two weeks +) we could really do with a zonal wave 2 anomaly right about now for colder weather in January. Surprise suprise right on cue.

Interesting that Brick,thanks.So a probable period of milder weather then hopefully a reload of cold in the new year?

If the jet stays south maybe the intermediate spell may be more average rather than mild.

[SteveB]

Thanks for the update brick, some hope then for a further cold spell in Jan.

[chionomaniac]

The dramatic temperature rises seen forecast at the 30 hPa level at more southerly latitudes (Oslo, Bordeaux, Berlin) can sometimes be the first signs of a SSW. They certainly were last year! It's the right time frame too with the increase in wave 2 activity!

Worth keeping an eye on as it is in stratospheric FI presently.

c

[karyo]

I suppose most people are currently emphasizing on the current cold spell and snow possibilities that's why it's so quiet in here!

Latest forecast from the Berlin site is not looking good: http://strat-www.met.fu-berlin.de/cgi-bin/times?plot=temps&alert=1

currently below average stratospheric temperatures with no sign of warm up! I hope this changes soon...

Karyo

[bluearmy]

surface temps remain high and are likely to continue to do so as another block with its associated warmer uppers heads to the pole for next weekend.

[Glacier Point]

Some cooling projected and worth noting the shape of the polar vortex.

Currently, the vortex is very elongated and extends from Alaska to Scandinavia:

http://strat-www.met.fu-berlin.de/cgi-bin/ecmwf?alert=1&level=10&forecast=a12

Latest ozone concentration plots depict this shape with separate areas of high ozone:

Both GFS and ECM forecasts programme the shape of the vortex to expand and become less eliptical:

This may disturb the areas of ozone a little although we should expect to see a similar pattern. Note that the stratosphere in the tropics and extratropics remains cold and this should inhibit a strong stratospheric jet from developing.

Based on the profile of the vortex and the areas of high ozone, I think we should expect to see the lower stratosphere respond with ridges over Canada and east Asia and downstream troughs over the Pacific and Scandinavia. This shoud support troposheric ridges in similar areas, shifted slightly eastwards in the lower atmosphere. Reanalysis of years with a similar vortex in January yielded a blocking signal over Iceland.

[Mark Bayley]

So not all bad then GP?

Are we still expecting a SSW sometime around the start of January or end of December?

[azores92]

So not all bad then GP?

Are we still expecting a SSW sometime around the start of January or end of December?

doesnt look bad at all imo. does this mean the polar vortex can be displaced further west, with height rises continuing over iceland and greenland? as long as this happens, then surely it is game on? edit: looking at the analogues, a dry but cool/cold january was a theme shared between the years mentioned.

Edited December 19, 2009 by azores92

[weatherobsuk]

Im familiar with the terminology of SSW, but not the Characteristics (will be reading up on this forum in the coming few days however.)

But this past week Moscow has been seeing -20'c/-30'c temperatures to which some at the Russian Meteorological Agencies have been saying is a temperature Anomalie. Could this be the start of a cooling trend associated with a SSW, in which the UK is just missing out on at the moment due to cold pooling from the Arctic, but once the winds swing to a more Siberian flow again we could also see this Anomalie settling over the UK as we did in Feb 09.

[Mark Bayley]

Stratospheric temps look took to be remaining below average for the foreseeable future, which isn't great. Towards the very end of the forecast it does look like its slowly starting to rise (Probably nothing though) Wasn't a warming event was predicted around this time wasn't it?

[chionomaniac]

Stratospheric temps look took to be remaining below average for the foreseeable future, which isn't great. Towards the very end of the forecast it does look like its slowly starting to rise (Probably nothing though) Wasn't a warming event was predicted around this time wasn't it?

Interestingly, the tropospheric mean zonal winds remain reversed between 60-90ºN for the foreseeable future which still indicates a very displaced vortex. There is a difference of opinion between the GFS and ECM to what happens to the main polar vortex which is currently situated over Scandinavia.

c

Also looking at the possible downwelling of positive zonal mean wind anomalies, one would expect these to hit the troposphere around the start of January. This would be in possible conflict with the -NAO signal that GP has indicated that could be possible around that time. Hopefully they won't be that strong by the time they reach the troposphere.

[Methuselah]

'Morning ch...A quick Q:

How much stratospheric cooling is required, in order to cause the pattern we currently have to break down? Or, without any further warmings, will it just revert to the usual cack?

[chionomaniac]

'Morning ch...A quick Q:

How much stratospheric cooling is required, in order to cause the pattern we currently have to break down? Or, without any further warmings, will it just revert to the usual cack?

That's far too complex a question to give a simple answer to, Pete! I don't think there is any set rule. We have many modifiying factors on the stratospheric vortex strength this winter. There is the easterly QBO, the colder than average tropical stratosphere and increased polar ozone due to the increased BDC. All these could modify any set increase in vortex strength and how it affects the troposphere. I suspect that the increased positive mean zonal winds will propagate down to the troposphere during early January and could possibly give us zonal conditions then - but this all depends on whether other tropospheric teleconnections are overridden. Still waiting to see if any warming occurs but I feel that this is less likely than it was looking at the start of the month.

c

[Methuselah]

Thanks ch...

[MR EXTREMES]

oh dear not looking good for january so far just goes to show how quickly things change.

over all had something early this year.

but i fear this will be our best chance for prolonged cold and its 99% sure of sliding away.

maybe a strat warming event will happen but looking at whats be suggested its looking not so good now what a shame.

i fear if nothing comes of in january the rest of winter will follow suit.

still its a very intresting subject i expect nino is tampering with the strat in someway,

after all this is the month where nino takes full effect.

Edited December 20, 2009 by badboy657

[azores92]

oh dear not looking good for january so far just goes to show how quickly things change.

over all had something early this year.

but i fear this will be our best chance for prolonged cold and its 99% sure of sliding away.

maybe a strat warming event will happen but looking at whats be suggested its looking not so good now what a shame.

i fear if nothing comes of in january the rest of winter will follow suit.:blink:

still its a very intresting subject i expect nino is tampering with the strat in someway,

after all this is the month where nino takes full effect.

why the pessimism? just because the stratosphere is cooler at the moment doesnt automatically secure wet and windy conditions further down the line. the teleconnections havent all been conducive of a raging polar vortex, with high pressure over europe. besides, december played out far differently to the forecasts, and just goes to show that in an el nino winter the weather doesnt always play by the rules. it could be that a surface high could settle over the uk, or we could reenter another cold spell, and going by gps post yesterday, i dont think zonality is the form horse. its not as clear cut as cool stratosphere- raging westerlies, warm stratosphere-northern blocking.

Edited December 20, 2009 by azores92