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Posted
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
  • Weather Preferences: Snow and storms
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.

Next update, and another good one.

First forecast charts to look at are the mean zonal wind forecasts. These are averaged out across the whole northern hemispheric stratosphere and troposphere. The oranges are positive westerly winds and the blues are mean negative easterly winds. The area to concentrate on is the polar region in the troposphere (below 100 hPa) from 80-90º.

The first chart shows the current situation with a strong polar vortex close to the pole.

The next chart (at T+240) shows that the polar vortex has withdrawn somewhat allowing mean easterly winds around this area. This signifies Northern Blocking across the high latitude.

When we look at the T+240 100 hPa chart below we can see the shape that the underlying tropospheric vortex will conform to. And for Nick Sussex, it is easier in this chart to make out where a possible block would occur (around Greenland) with a weak trough around the UK suggesting a cold northerly airflow (jet directed) towards the UK.

All in all, a very promising situation when one considers that it is in tune with the MJO/GWO forecasts. I do think that, even though there is no deep cold built up over the continent, it is possible to get significant cold to our shores but that it all depends upon the subtleties of the exact sequence that the block is built up in.

c

Edited by chionomaniac
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Posted
  • Location: st albans
  • Location: st albans

Next update, and another good one.

First forecast charts to look at are the mean zonal wind forecasts. These are averaged out across the whole northern hemispheric stratosphere and troposphere. The oranges are positive westerly winds and the blues are mean negative easterly winds. The area to concentrate on is the polar region in the troposphere (below 100 hPa) from 80-90º.

The first chart shows the current situation with a strong polar vortex close to the pole.

The next chart (at T+240) shows that the polar vortex has withdrawn somewhat allowing mean easterly winds around this area. This signifies Northern Blocking across the high latitude.

When we look at the T+240 100 hPa chart below we can see the shape that the underlying tropospheric vortex will conform to. And for Nick Sussex, it is easier in this chart to make out where a possible block would occur (around Greenland) with a weak trough around the UK suggesting a cold northerly airflow (jet directed) towards the UK.

All in all, a very promising situation when one considers that it is in tune with the MJO/GWO forecasts. I do think that, even though there is no deep cold built up over the continent, it is possible to get significant cold to our shores but that it all depends upon the subtleties of the exact sequence that the block is built up in.

c

can you find the equiv GFS/GEM offerings Ch? the 00z ecm T240 has a strong omega block (not surprising, looking at the chart you attached). the GEFS 00z is much less amplified and the 06z even more so. the NAEFS also is progressive with the block so the GEM can't be that keen either (just checked it on meteociel and its failry similar to the 06z GEFS). given such a disagreement this morning, where does your experience of the strat modelling lead you to believe we are headed ???

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Posted
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
  • Weather Preferences: Snow and storms
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.

can you find the equiv GFS/GEM offerings Ch? the 00z ecm T240 has a strong omega block (not surprising, looking at the chart you attached). the GEFS 00z is much less amplified and the 06z even more so. the NAEFS also is progressive with the block so the GEM can't be that keen either (just checked it on meteociel and its failry similar to the 06z GEFS). given such a disagreement this morning, where does your experience of the strat modelling lead you to believe we are headed ???

At T+240 we are very much out into FI even with the strat forecasts, Nick. Forecasts become more reliable the higher that you go in the stratosphere, and the closer the timeframe is. Having said that the forecasts tend to be more reliable than the tropospheric equivalents. The ECM forecasts that we see today (annoyingly) are from yesterdays 12Z run whilst the GFS forecasts are from that days 00Z run. There is no GEM offering as far as I am aware.

The elongated polar vortex forecast for the middle stratosphere on the GFS is still present on the latest run and, reassuringly, the 100 hPa T+240 forecast looks very similar to that of the ECM.

c

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Posted
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
  • Weather Preferences: Snow and storms
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.

I am going to try out a forecast here for the stratosphere for around 15 days time before anything is picked up by the models. This is very experimental on my behalf, but I have been monitoring the stratosphere long enough now to give it a shout.

Currently we are about to see a slight warming of the stratosphere in around 5 days time that is responsible for the elongation of the vortex seen at the 10 hPa level down to the troposphere. I believe that this warming was caused by an increase in wave number 2 activity due to a wave breaking into the stratosphere following a strong positive Asian mountain torque event.

Looking at the phase of the GWO I believe that we are now going to experience a strong negative asian mountain torque event which again is going to cause another wave number 2 to break into the stratosphere. This is likely to cause another warming of the stratosphere in around 15 days time before it has had a chance to cool down from the present warming. This is likely to cause further disturbances with the tropospheric vortex right up until the middle of December, with phases of Northern blocking right up until this time and possibly Christmas.

As I have said, this is very experimental but I feel nothing ventured, nothing gained!

I will let you know how quickly that I will be wiping the egg off my face.

c

PS, GP, Do you know if there is any way of predicting a strong Asian torque before it has happened? Are there any forecasts for instance? Thanks!

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Guest harshwinter09

Wow, chio, it seems you are getting to grips with the technical stuff too.

I hope you are right.

Let's hope its not just ozone levels which are the only factor to help warm the statosphere.

Here's hoping GP doesn't become a thundercloud when he replies to your post and dampens our spirits.

Good luck with your prediction.

Edited by harshwinter09
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Given we're going to have a La Nina near or at record levels, I think a very cold stratosphere and resulting positive AO is just something we're going to have to deal with winter.

If this is a "double dip" La Nina, as I suspect it might be, we could be in for two winters of raging positive AO's and very intense PV's.

I wonder where your very intensive PV's and raging positive AO's have gone no sign of it at all on current output.

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Posted
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
  • Weather Preferences: Snow and storms
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.

Could someone please explain to this ignoramus what a 'mountain torque ' event is.....tar very much.

Hi gb, you are not an ignoramus at all - it has taken me years to get a grasp of this!

In order to understand mountain torque effects one needs some understanding of Rossby waves first. These are large scale planetary waves that are effectively kinks in the upper air westerlies that circumvent the hemispheres. Each bend in the flow is a Rossby wave of which there are normally two (but may be more or less) in the NH due to the two land masses.

When a Rossby wave meets a mountain range it effectively has a hurdle to clear. Some of the energy of this wave may be absorbed by the mountain range whilst other energy can be deflected polewards, into the tropics and absorbed, or into the stratosphere. The larger the wave that hits a mountain range, the larger the sequelae. So if a strong enough wave hits a mountain range then this wave can 'break' into the stratosphere cause an effect up there - notably a warming and disruption to the vortex. The disruption of the Rossby wave when it hits a mountain range is known as a mountain torque and can be positive or negative depending on whether the trough or ridge hits the mountains. This plays an important part of the GWO system by removing or adding energy to the middle latitudes through this process.

There is still good disruption showing on the stratospheric vortex today right up to the top level where the stretching of the vortex is extremely impressive. It is as a good a time for it to take another hit as any!

The 100 hPa chart at T+240 looks as good as any that I have seen for the placement of any blocking.

One can follow through the distorting of the vortex as the warming occurs through this series of 10 hPa charts

http://wekuw.met.fu-berlin.de/~Aktuell/strat-www/wdiag/ec.php?alert=1&level=10&forecast=all&lng=eng

All in all a lot to look forward to in the coming weeks.

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Posted
  • Location: Nuneaton,Warks. 128m asl
  • Weather Preferences: Snow then clear and frosty.
  • Location: Nuneaton,Warks. 128m asl

Thanks again for your posts C.

Every new one helps shine a little more light on this subject for me.

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Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

Hi gb, you are not an ignoramus at all - it has taken me years to get a grasp of this!

thanks chio-just the sort of explanation we all need as we try to get to grips with this fascinating world of trying to predict several weeks ahead.

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Posted
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
  • Weather Preferences: Snow and storms
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.

That is a very good simplified explanation - the kind that has helped me understand these processes.

One thing - you mention above in terms of your prediction that following the positive mountain torque which has initiated the wave break to assist with this upcoming blocking, there could be another wave break courtesy of a negative mountain torque.

Is the effect in terms of potentially disturbing the vortex consistent with both positive and negative mountain torques?

Thanks (sorry if I haven't read this right!)

We are reaching the limits of my knowledge here, but the amplitude and direction of the approaching Rossby wave will be the most important factor when hitting a mountain range. So yes, whether there is a strong negative or positive mountain torque with resultant wave breaking into the stratosphere being the most important factor. I guess that I am looking to see a strong negative Asian torque in the coming days if my predication is going to come near to verifying.

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Posted
  • Location: hertfordshire
  • Location: hertfordshire

As far as I understand things it is troughing or whatever that enable large planetary or rosby waves

to push into the high latitudes where upon they break in the stratosphere and some energy is

deflected back towards the equator while other energy breaks in the polar stratosphere.

How much goes where depends a lot on QBO and solar enviorment in the stratosphere.

Large positive and negative torques such as a large PNA ridge for example are a indication of this

process.

If you look on the Meteociel GFS northern hemisphere charts you will see this in action at the start

of the run as high pressure (warmer air and higher ozone ) is forced upwards and into the Arctic

from far eastern Siberia and the Bering strait side of the globe. The effects of this are shown by the

increased heights over the Arctic in the latter time frames.

Edited by cooling climate
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Posted
  • Location: Eccles, Greater manchester.
  • Location: Eccles, Greater manchester.

Hi gb, you are not an ignoramus at all - it has taken me years to get a grasp of this!

In order to understand mountain torque effects one needs some understanding of Rossby waves first. These are large scale planetary waves that are effectively kinks in the upper air westerlies that circumvent the hemispheres. Each bend in the flow is a Rossby wave of which there are normally two (but may be more or less) in the NH due to the two land masses.

When a Rossby wave meets a mountain range it effectively has a hurdle to clear. Some of the energy of this wave may be absorbed by the mountain range whilst other energy can be deflected polewards, into the tropics and absorbed, or into the stratosphere. The larger the wave that hits a mountain range, the larger the sequelae. So if a strong enough wave hits a mountain range then this wave can 'break' into the stratosphere cause an effect up there - notably a warming and disruption to the vortex. The disruption of the Rossby wave when it hits a mountain range is known as a mountain torque and can be positive or negative depending on whether the trough or ridge hits the mountains. This plays an important part of the GWO system by removing or adding energy to the middle latitudes through this process.

There is still good disruption showing on the stratospheric vortex today right up to the top level where the stretching of the vortex is extremely impressive. It is as a good a time for it to take another hit as any!

The 100 hPa chart at T+240 looks as good as any that I have seen for the placement of any blocking.

One can follow through the distorting of the vortex as the warming occurs through this series of 10 hPa charts

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

All in all a lot to look forward to in the coming weeks.

thankyou,..so what causes 'rosby waves'.?...

Edited by greybing
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Posted
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
  • Weather Preferences: Snow and storms
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.

thankyou,..so what causes 'rosby waves'.?...

3.4.1 Standing Planetary Waves and Wave Breaking -- One type of atmospheric wave that exists is called the Rossby wave. Named for Carl G. Rossby, an early atmospheric research scientist, the Rossby wave exists due to a combination of meridional temperature gradients and the rotation of the planet (which produces the Coriolis force). The Rossby wave is a large-scale wave system whose size is thousands of kilometers in the horizontal and several kilometers in the vertical.

Large-scale topographical features, like the Rocky Mountains and the Himalaya-Tibet complex, together with the meridional temperature gradients and Coriolis deflection, create a variation of Rossby waves called standing planetary waves. These have very long wavelengths (up to 10,000 kilometers) and either remain stationary or move slowly westward (i.e., they move easterly). They eventually propagate vertically into the stratosphere.

Courtesy of http://www.ccpo.odu.edu/~lizsmith/SEES/ozone/class/Chap_6/index.htm

Also wiki explanation http://en.wikipedia.org/wiki/Rossby_wave

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Posted
  • Location: Eccles, Greater manchester.
  • Location: Eccles, Greater manchester.

3.4.1 Standing Planetary Waves and Wave Breaking -- One type of atmospheric wave that exists is called the Rossby wave. Named for Carl G. Rossby, an early atmospheric research scientist, the Rossby wave exists due to a combination of meridional temperature gradients and the rotation of the planet (which produces the Coriolis force). The Rossby wave is a large-scale wave system whose size is thousands of kilometers in the horizontal and several kilometers in the vertical.

Large-scale topographical features, like the Rocky Mountains and the Himalaya-Tibet complex, together with the meridional temperature gradients and Coriolis deflection, create a variation of Rossby waves called standing planetary waves. These have very long wavelengths (up to 10,000 kilometers) and either remain stationary or move slowly westward (i.e., they move easterly). They eventually propagate vertically into the stratosphere.

Courtesy of http://www.ccpo.odu....hap_6/index.htm

Also wiki explanation http://en.wikipedia....iki/Rossby_wave

thankyou.

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Posted
  • Location: Worcestershire
  • Weather Preferences: Forecaster Centaurea Weather
  • Location: Worcestershire

I am going to try out a forecast here for the stratosphere for around 15 days time before anything is picked up by the models. This is very experimental on my behalf, but I have been monitoring the stratosphere long enough now to give it a shout.

Currently we are about to see a slight warming of the stratosphere in around 5 days time that is responsible for the elongation of the vortex seen at the 10 hPa level down to the troposphere. I believe that this warming was caused by an increase in wave number 2 activity due to a wave breaking into the stratosphere following a strong positive Asian mountain torque event.

Looking at the phase of the GWO I believe that we are now going to experience a strong negative asian mountain torque event which again is going to cause another wave number 2 to break into the stratosphere. This is likely to cause another warming of the stratosphere in around 15 days time before it has had a chance to cool down from the present warming. This is likely to cause further disturbances with the tropospheric vortex right up until the middle of December, with phases of Northern blocking right up until this time and possibly Christmas.

As I have said, this is very experimental but I feel nothing ventured, nothing gained!

I will let you know how quickly that I will be wiping the egg off my face.

c

PS, GP, Do you know if there is any way of predicting a strong Asian torque before it has happened? Are there any forecasts for instance? Thanks!

Agree with this Ed.

We are due another +ve mountain torque in the late November / early December timeframe, probably the last before a strong -ve tendency to the base state returns. If we look Empircal Wave Propagation plots, we might get some sense of when convective instability will return to the Indian Ocean:

The plot suggests the period late November through 8th December looks favourable. If the GWO is reasonably cooperative, poleward fluxing should be the mechanism to induce a strong +ve torque as westerlies are added to the Asian Jet and Pacific flow 30N - 40N.

Latest ozone plot looks really good for cold signallng into December, just a smidge down on where we were last year for the Arctic with the Aleutian / NW Pacific ridge really noticeable which should enhance the mid / high latitude ridges.

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Posted
  • Location: Stourbridge
  • Location: Stourbridge

Agree with this Ed.

We are due another +ve mountain torque in the late November / early December timeframe, probably the last before a strong -ve tendency to the base state returns. If we look Empircal Wave Propagation plots, we might get some sense of when convective instability will return to the Indian Ocean:

The plot suggests the period late November through 8th December looks favourable. If the GWO is reasonably cooperative, poleward fluxing should be the mechanism to induce a strong +ve torque as westerlies are added to the Asian Jet and Pacific flow 30N - 40N.

Latest ozone plot looks really good for cold signallng into December, just a smidge down on where we were last year for the Arctic with the Aleutian / NW Pacific ridge really noticeable which should enhance the mid / high latitude ridges.

Hi GP, does this mean by the 8th december the best chance of sustained cold could have come and gone?

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Posted
  • Location: st albans
  • Location: st albans

Hi GP, does this mean by the 8th december the best chance of sustained cold could have come and gone?

the drivers referred to by GP and Chio are precusrors of events in the polar strat by some weeks and would likely take us to the end of dec.

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Posted
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet
  • Location: Leeds/Bradford border, 185 metres above sea level, around 600 feet

Hi GP, does this mean by the 8th december the best chance of sustained cold could have come and gone?

Most telleconections seem to have around a twenty day lag before impacting the polar atmosphere, thus we would be looking at the majority of December looking good for cold spells.

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Posted
  • Location: Stourbridge
  • Location: Stourbridge

Most telleconections seem to have around a twenty day lag before impacting the polar atmosphere, thus we would be looking at the majority of December looking good for cold spells.

Okey doke, perhaps making january and february slightly less favourable, hanging on to the hope of a surface high?

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Posted
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.
  • Weather Preferences: Snow and storms
  • Location: Hayward’s Heath - home, Brighton/East Grinstead - work.

Really interesting charts again today which remind me a lot of lest December.

Firstly, it is worth looking at the GFS's offerings. The GFS is suggesting a vortex split extending from the troposphere into the middle layers of the stratosphere (up to 30 hPa by T+192). Now it was emphasized last year, that these splits are not transient affairs that will quickly dissipate. They are extensive disruptive activities of the polar vortex that can completely disrupt the normal flow of the vortex. When the vortex splits this time, the main area that pressure builds is in the North Atlantic - not the North Pacific. Why not ? Could this possibly be a beneficial side affect of the La Nina?

The GFS 100 hPA charts which correlate closely with those of the troposphere show that the split occurs at T+168

The above chart shows the split and where the Greenland High is likely to form. Now, from here on, the GFS has suggested various routes, but the 12Z GFS today has been the closest in matching the lower strat output. This suggests that the GH block will migrate slightly eastwards, but undercutting will still occuras the T+240 chart suggests.

The ECM at the same timeframe possibly shows a better disrupted vortex shape

These two charts are fairly similar - perhaps we will see a hybrid of both. Cold is never guaranteed with either, however, this type of set up will give us the best chance of any cold air displaced from the Arctic circle heading south.

Heading further up the stratosphere I do see an increase in wave number 2 activity as I thought might occur - I will need to keep an eye on the mountain torques in the coming 10 days.

http://wekuw.met.fu-berlin.de/~Aktuell/strat-www/wdiag/eczm.php?alert=1&forecast=all&var=ha2&lng=eng

It does look like there could be another warming waiting in the wings at the 10 hPa level but further forecasts needed here.

http://wekuw.met.fu-berlin.de/~Aktuell/strat-www/wdiag/ec.php?alert=1&level=10&forecast=all&lng=eng

All in all a very promising situation developing for cold lovers for the start of the winter.

c

Edited by chionomaniac
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Posted
  • Location: Camborne
  • Location: Camborne

Still trying to get to terms with some of this so forgive me if I ask the obvious questions. You mention that firstly, it is worth looking at the GFS's offerings. The GFS is suggesting a vortex split extending from the troposphere into the middle layers of the stratosphere (up to 30 hPa by T+192). Not doubting that for one moment but as the troposphere is very shallow in the arctic winter can I assume that this is from the surface upward?. In other words the vortex (and split) are obvious at all levels. I had a quick look at the 700 and 300mb charts for midnight as an example,

Edited by weather ship
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