chionomaniac

Interestingly, and this doesn't happen often, the average surface temperatures could be lower than the 850hPa temps on some of those days in some areas.

I have a guarded expectation for a SSW in Feb. Technically, the closer that the solar flux is to the higher cut off of 150, the better.

I was going to update today as well suggesting something similar guys. The stratosphere is behaving true to form and as one would expect this early in the season. The cooling is driving the strong vortex conditions and the wave activity is just not strong enough to disrupt the vortex enough. If we remember the feedback mechanism described in the first post, then this year will be a true examination of that process. Come January, then I suspect that we will see greater vortex distortion from increased wave 2 activity - this will improve with seasonal wavelength changes through winter as they increase with amplitude as we progress.

A) you use the word again - but the last few years winters haven't been disappointing. B ) winter is only 5 days old - so even with the best computers forecasts, the 12th Dec is as far as one could reliably predict leaving another 78 days that improvements could be gained. C) perhaps you could find the correct thread to moan into as this thread is for discussion, not moaning.

Ahh, so you have found proof of this now Shed! Yet again this is your assumption - please can you provide statistical proof that this is the case.

I have to admit, Jo - when Tony put that page up, I didn't even look at the headline!!

That's my primary analog year from the winter forecast.

I have to say CH, I am not as optimistic as you are looking at the strat charts. Firstly, in todays Berlin output which is based on yesterdays 12Z ECM, the best that I can see is any height rises to our NE being positioned too far south and the residual Canadian vortex position also unfavourably positioned to allow further height rises any further north. This is backed up somewhat by the latest GFS charts: I don't think that the wave 2 activity will be strong enough to weaken the vortex sufficiently.

No it will be easterly.

Would agree entirely on the thoughts that the GFS under amplifies by 2/3rds whilst the ECM over amplifies by a 1/3rd, Steve. No model is perfect, but interestingly it is this issue that so often can create all the heated discussion in this thread. And quite often the UKMO is that model in the middle - it's just that it only goes to T+144!

The biggest change is with the GEM ensembles though, Steve. Will need to wait until they are in day 10 range because at day 10 the 12Z Euro ensembles have consolidated the Scandi positive anomaly compared to the 00Z. Oh and Steve - I don't necessarily think that this is a case of eastward bias - rather just 'routine' unpredicatability when the outputs are searching for the pattern. And to show the ECM day 10 anomalies 00Z 12Z oppsite direction to the NAEFS!!!

Anyone spot the big shift in the NAEFS 11-15 day anomalies between the 00Z and 12Z runs? 00Z 12Z Even the cumulative anomaly charts are jumping around - these should be the most dampened of the lot without such interrun variance. Big reduction in the strength of the Scandi anomaly. Doesn't mean that it is anywhere near correct though.

I think that they are dancing happily together presently - the strat is behaving as would be expected per analog years and the tropospheric response measures up quite well too. Wave activity rebounds into the strat every winter and this is no different. CH's excellent post earlier in the thread shows this very well. I suspect that any strong Scandi ridge signal may be slightly over emphasised by the output - but later on in the season I wouldn't.

Just an update. I constructed most of the composites for the winter forecast back in September and wrote most of the winter forecast at the start of November. I waited until a little bit later in the month before seeing if there were to be any late significant changes - but in the end I didn't make any (written component was finished a fortnight ago today). I also constructed some analog composites for November to see how on track the forecast would be and it seems a good time to compare these to what has actually occured in the lead up to winter. So first stratospherically, we should compare the 30 hPa temps and height anomalies Forecast 30 hPa temp analog Actual Verdict - temperature pattern is the same but cooling is greater. Forecast 30 hPa height anomaly Actual Verdict - positive height anomalies further west over wEurasia rather than east - but close pattern once again. Now onto the 500 hPA pattern Forecast : Actual A significant difference here - not over the Atlantic sector - the anomalies are quite similar when the scale is taken into consideration. However, the Pacific positive height anomaly is considerable stronger, as is the polar vortex negative anomaly. The strong Pacific ridge may help later on in winter. Next to look closer to home: Euro 1000hPa forecast anomaly: Actual Verdict: Pretty close And Euro temp forecast anomaly: Actual Verdict - very similar pattern (with a lot warmer Arctic if you look closely) So overall a fairly similar pattern match, with the most notable difference being the strength of the pacific ridge height anomaly. Whether this will assist feedback into the stratosphere later in winter remains to be seen. I suspect that we may be a week or two behind timing wise as well, but currently I wouldn't change the original forecast on this.

Anyone looking at the UKMO this morning who remembers the debate about yesterdays 12Z will be intrigued to see that the UKMO has dropped the idea of the 75% of energy over the top. We now have a more uprighted Atlantic trough and deeper cold down the UK as a result.

Something in this area Nick?

Not really a good example to show an undercutter, gltw. I can't say that it isn't at that point but can't say that it is either. A very weak attempt at some form of WAA occurs so I wouldn't use that as an example.

It's a new one - the half toppler...

Worth looking at that T+144 UKMO chart that I highlighted earlier and comparing to the ECM So here is the UKMO chart again - remember the 75% of energy in the form of the shallow depression over the ridge: Well it's not there on the ECM which will keep the cold flow more meridional and it will last longer. With no agreement like that FI is well inside that timeframe as well!! It renders the earlier difference of opinion quite pointless also. Good to have debate though.

Right, I have just analysed the UKMO T+120 and T+144 charts to see what all the fuss is about. There is no need to get into a big personal argument about it chaps because by the time the next UKMO runs again, no doubt that there will be further changes - so in effect you will never know what the UKMO T+168 would show! My take on it ? Well look at the T+120 and we see the offending low off the eastern seaboard: Which way does it go by the next frame T+144. Well by my look 75% of the jetstream energy goes over the block with the resultant 25% going under. That would tend to suggest that no undercutting would occur and the block would travel east before flattening. But we all know that in another 12 hours the charts may look completely different as they try to get to grips with what actually is going to happen and therefore we can't rule out the 25% option anyway.

A good post and one that I agree with. Any SSW this winter is the long shot call. Another similar year to look at is Feb 1979, neutral ENSO, -ve PDO. There was far less of the Kamchatka vortex and stronger Bering ridging that year. Strong enough for an early FW as well in the Berlin archives (though not according NASA) Big wave 2 activity - but it took two attempts to break the vortex one at the end of Jan and the other at the end of Feb that finally succeeded. It's a pity that we can't see what happened wave wise earlier that winter. Those concentrating on the favourite this winter should just keep an eye on their blind side that the long shot doesn't creep up on them!

Furthermore to the last post it is worth demonstrating how strong the wave 1 activity has to be before we really see significant vortex displacement. Looking so far this year we can see that there have been a number of bursts of stronger wave 1 activity. The strongest was at the start of the year and was responsible for the well predicted and monitored SSW in January ( see below). The second burst was not as strong but was very significant - at the start of March just as the vortex was recovering and we all know what happened after that. This autumn we have seen some smaller bursts of wave 1 activity - but nothing out of the ordinary - but I suspect that the next round will be stronger still. Also included below is the mean zonal mean wind anomaly chart which demonstrates quite nicely the propagation of the negative mean zonal winds from the top of the strat to the trops - note the recharge at the start of March from the wave 1 activity.

That is a 10hPa chart from the latest GFS run, Snowman. It is a temperature forecast only and does not include mean zonal winds. These can be found through the ECM link on the first post. Interesting the 10 day ECM forecast at 1hPA shows the wave distortion forecast at the top of the strat - the biggest of the season so far. Will watch this one as it may get down as far as 5-10hPa.

It's the passage way between the bar and the WI meeting room. OR Greenland Iceland Norway sea area

No - just some yellow snow!