I always like to look at this chart:

http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/index.html

Current forecast is off the chart at the moment (but it is a forecast nonetheless):

Originally Posted by: Maunder Minimum 

Is there anything on wind reversal?  As I understand it that's the important measure.

Originally Posted by: Gandalf The White 

Is there anything on wind reversal?  As I understand it that's the important measure.

Originally Posted by: Gandalf The White 

Yup - here's the companion chart to that ECM one (also from the ECM and available here - go to the 60N zonal wind and fluxes chart)

If you check the 10hPa T+240 chart from the same link, ECM is forecasting an SSW with a split vortex... this is the first day it's come in range, although the past few days have shown a reversal right at the top (1hPa).

EDIT: And the 1hPa chart is a work of art, showing a circular high just off from the pole by 240 - with several vortices rather than one big one.

Originally Posted by: Retron 

Thanks Darren, that's helpful.

So now we wait for the wind reversal to happen and then for it to propagate down into the troposphere and see what effects it produces.

As you said in the MOD thread, this is potentially more significant as we're just approaching the peak of the northern hemisphere winter.

Originally Posted by: Gandalf The White 

This is also of interest - note the magnitude of the negative zonal wind:

Trop charts are hugely dispiriting at the moment, but surely there has to come a point where it responds to the SSW when it occurs - when that happens, let's hope the nasty Iberian HP cell gets eaten alive!

Originally Posted by: Maunder Minimum 

Yes but that big reversal is very high up in the stratosphere at 1hPa which is no use to us at all. What we need to see is that reversal propagating down to the troposphere. So the second chart showing the position at 10 and 30hPa is of more interest. We do see a reversal just starting to take place at 10hPa by the end of the forecast period.

I find the charts below more helpful.

The first one is the actual position at 12z yesterday

http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwfzm_u_a12.gif

What we are interested in is the zonal wind between 60N and 90N. There is a very strong zone of solar wind centred around 50N at 1hPa

If we look out to 5 days (i.e. 24 Dec) we see this

http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwfzm_u_f120.gif

A significant change. We now have a reversal at 1hPa all the way from 60N to 90N. On the other hand there is strong positive zonal wind around 75-80N at 10hPA.

By day 10 the negative zonal wind is really starting to propagate down all the way to 10hPa.

http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwfzm_u_f240.gif

If that trend continues it would not be long before it reached 30hPa. After that we might start to see some impact on the troposphere and potentially the model output.

Typically it takes about two weeks from the midpoint of a SSW for any noticeable impact to be seen in the troposphere, although it can be quicker. The peak temperature at 10hPa over the Pole is projected to be around Boxing Day. 2 weeks after that would take us to 9/10 January. 

Currently the GFS only goes out to 5 January. So I am not at all surprised there is nothing doing in the models at present. Even when 9/10 Jan comes into range any fluctuations will likely just be noise initially given there is usually a lot of scatter at T384. So I think it will be at least another week before any consistent signs of a significant cold spell might start showing up in the GEFS. That is of course assuming that any blocking that may occur happens in the right place to affect the UK. It is possible we will see no impact at all in our neck of the woods.

Personally I am not going to get interested in what the models are showing until after Christmas. 

Originally Posted by: Global Warming 

Excellent post, thanks GW

Originally Posted by: Whether Idle 

Yes but that big reversal is very high up in the stratosphere at 1hPa which is no use to us at all. What we need to see is that reversal propagating down to the troposphere. So the second chart showing the position at 10 and 30hPa is of more interest. We do see a reversal just starting to take place at 10hPa by the end of the forecast period.

I find the charts below more helpful.

The first one is the actual position at 12z yesterday

http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwfzm_u_a12.gif

What we are interested in is the zonal wind between 60N and 90N. There is a very strong zone of solar wind centred around 50N at 1hPa

If we look out to 5 days (i.e. 24 Dec) we see this

http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwfzm_u_f120.gif

A significant change. We now have a reversal at 1hPa all the way from 60N to 90N. On the other hand there is strong positive zonal wind around 75-80N at 10hPA.

By day 10 the negative zonal wind is really starting to propagate down all the way to 10hPa.

http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwfzm_u_f240.gif

If that trend continues it would not be long before it reached 30hPa. After that we might start to see some impact on the troposphere and potentially the model output.

Typically it takes about two weeks from the midpoint of a SSW for any noticeable impact to be seen in the troposphere, although it can be quicker. The peak temperature at 10hPa over the Pole is projected to be around Boxing Day. 2 weeks after that would take us to 9/10 January. 

Currently the GFS only goes out to 5 January. So I am not at all surprised there is nothing doing in the models at present. Even when 9/10 Jan comes into range any fluctuations will likely just be noise initially given there is usually a lot of scatter at T384. So I think it will be at least another week before any consistent signs of a significant cold spell might start showing up in the GEFS. That is of course assuming that any blocking that may occur happens in the right place to affect the UK. It is possible we will see no impact at all in our neck of the woods.

Personally I am not going to get interested in what the models are showing until after Christmas. 

Originally Posted by: Global Warming 

Yes but that big reversal is very high up in the stratosphere at 1hPa which is no use to us at all. What we need to see is that reversal propagating down to the troposphere. So the second chart showing the position at 10 and 30hPa is of more interest. We do see a reversal just starting to take place at 10hPa by the end of the forecast period.

I find the charts below more helpful.

The first one is the actual position at 12z yesterday

http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwfzm_u_a12.gif

What we are interested in is the zonal wind between 60N and 90N. There is a very strong zone of solar wind centred around 50N at 1hPa

If we look out to 5 days (i.e. 24 Dec) we see this

http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwfzm_u_f120.gif

A significant change. We now have a reversal at 1hPa all the way from 60N to 90N. On the other hand there is strong positive zonal wind around 75-80N at 10hPA.

By day 10 the negative zonal wind is really starting to propagate down all the way to 10hPa.

http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwfzm_u_f240.gif

If that trend continues it would not be long before it reached 30hPa. After that we might start to see some impact on the troposphere and potentially the model output.

Typically it takes about two weeks from the midpoint of a SSW for any noticeable impact to be seen in the troposphere, although it can be quicker. The peak temperature at 10hPa over the Pole is projected to be around Boxing Day. 2 weeks after that would take us to 9/10 January. 

Currently the GFS only goes out to 5 January. So I am not at all surprised there is nothing doing in the models at present. Even when 9/10 Jan comes into range any fluctuations will likely just be noise initially given there is usually a lot of scatter at T384. So I think it will be at least another week before any consistent signs of a significant cold spell might start showing up in the GEFS. That is of course assuming that any blocking that may occur happens in the right place to affect the UK. It is possible we will see no impact at all in our neck of the woods.

Personally I am not going to get interested in what the models are showing until after Christmas. 

Originally Posted by: Global Warming 

What a great post - thankyou. Very informative. People need to read this before posting in the MOD thread.

Originally Posted by: Whiteout 

Does anyone know of there were any SSW events at all between the one of mid-February this year and the one of early 2013 (think it was in January 2013 but am not sure)?

I seem to recall at leasr a couple of occasions during those few years when possible such events were discussed quite openly on here, but perhaps did not come to fruition.

Originally Posted by: David M Porter