chionomaniac

Yep - you win the prize!

Thanks for the feedback. I guess when compiling a forecast one has to take the rough with the smooth - especially when it is not predicting snowmageddon! When Paul asked me to provide a winter forecast back in the summer, I instantly assumed that it would be mild all the way this winter - even I was surprised when I looked at it in a bit more detail and saw that analogue years were suggesting an average to below average winter. Here's hoping that it is colder than the forecast suggests!!

I don't think that anyone has said that there is no sign of cold, CC. More so, and Gibby is right here, - there are no signs in the current output of long term sustained severe cold for the UK - ie the such that favourably positioned HLB's would produce. Any one who suggests otherwise is kidding themselves. That does not mean that we will not see a spell of below average temperatures - in fact I believe that December will come in slightly below average due to the NW/ SE orientation of the jet stream and those further north are likely to see some tempreratures cold enough for snow at times. There were a couple of good posts from CH and SM earlier that mentioned the stratosphere and wQBO and how that colder oulooks are still possible in spite of the current stratospheric conditions, but sustained HLB's are unlikely in the immediate.

I would call that neutral Gavin - ie average NAO conditions.

Are you basing the end of ridge domination and the return of zonality on the ensembles Shed? Because that is not what I see, more a continuance of the ridge after a brief weakening. And why do you say that most of us won't be too disappointed to see the gradual onset of zonality when you jolly well know that most of us would much prefer cold synoptics to show - or have you completed a private poll of MOD members wishes that only you are privy too?

4.1ºC please

No, in fact you are wrong Irish lad. Cohen's work originally focussed on the Eurasion snow cover extent (SCE) and then moved onto the Snow Advance Index (SAI). Both of these could be calculated at the end of October and correlated with the following winters AO. Whereas the correlation may not be 100% it is sufficient to give us an idea where winter may be headed wrt the AO. Picking on one day in November, before winter has even started, when the AO has just dropped below 0 and then trying to suggest that this is indicative of the whole winters AO is possibly a little short sighted. I am sure that Cohen's papers are linked in the technical papers thread - perhaps if you search them out then you will have a better understanding of the principles and theory involved.

I have been busy with work, home life and winter preparation, Matt, but you are right in a way, there is nothing to get too excited with stratospherically wise currently. Not that I expected there to be at this stage of winter. November tropospherically was always likely to be dominated by the Atlantic ridge and so this has occurred (is occurring). It fits in nicely with the wQBO, neutral ENSO and similar solar flux years. The flattened pattern is no surprise and the attempts of increased amplification are tending to get blown away by the developing stratospheric vortex. The recent wave 2 forecast is a prime example - the tropospheric wave was just not strong enough to make sufficient inroads into the core of the upper vortex. I suspect that we will see another MT event in the next 2 weeks leading to another amplification of the Rossby waves around early December and another attempt of waves trying to disrupt the vortex. But I am not expecting any HLB's in the next 4 weeks for our sector - but that doesn't necessarily mean blow torch either - more fluctuating MLB's. As Tamara has pointed out and I think I have mentioned previously this winter is likely to be dominated by a -ve EPO type pattern over the Pacific. This puts us downstream in an interesting position where one Atlantic pattern is unlikely to dominate over another ( would go for MLB's at a push). Still we could always be surprised and later on in winter is a time to look stratospherically to see if anything can develop. Funny enough, as well as time constraints, I have not been concentrating as much as normal on the stratosphere this winter because I simply not expecting anything to develop worth 'chasing' yet, but I am sure that will change after Christmas. It is with some increduality that I see the Armageddon type forecasts heralded about by certain media outlets and self acclaimed forecasters. Do they not factor stratospheric conditions at all in there foecasts? On another note I see that you have posted that the latest ECM 32 dayer has given a nondescript forecast for December and for once I think it could be right.

I suspect that it is just far more noticeable on a forum like this because the majority of members are far more interested in this type of pattern than the westerly pattern. I think that unless there is statistical evidence as CH suggests, then we won't really know.

Err No. I thought that you meant that westerlies are more likely to verify on computer models than other wind directions - but hadn't shown the statistical evidence to back this up. So is that not what you meant?

No, winds are more likely to occur from a westerly direction, not necessarily verify from a forecast on a computer model- there is a subtle difference - unless you can show me statistical evidence showing otherwise.

Over the last few years, Shed, westerlies have been continually been programmed to return following easterlies, south easterlies, northerlies etc and have been delayed and not verified at all. Please show me the statistic that shows the number of westerlies forecast, compared to the verification of said westerlies for the UK in FI, to back up your standpoint.

I have to say that this is not really a surprise given the lack of consistent support from the GFS. Still need to keep an eye on the future wave activity, but as I suggested in an earlier post, it is going to have to be mighty strong to overcome the vortex.

Just quickly - the heat flux is the transfer of heat in the area during a given timescale - so if it is large then that is beneficial over a given area eg meridional. That would mean that the transfer of heat from south to north is great and this can have vortex disturbance properties as any warming does in the stratosphere. Poor heat flux will not disturb the vortex as much. Substitute momentum for heat and the answer is similar.

Annoyingly, I deleted most of the early winter strat charts in that thread back in those early monitoring days so I can't compare to now - Do you remember them Tamara (or should I say Zebra Danio!!! from back then) I have checked and there was a large amount of autumnal wave 1 activity in 2008 but very little wave 2 activity. Still wouldn't rule out a SSW this year though.

The problem is at this time of year the upper vortex is so strong and still strengthening so that any wave activity is unlikely to break it down. Mind you, not that it needs to, as previous early winter trop induced lower strat splits have been very favourable here - but maybe not so in your neck of the woods. December SSW's are not exactly common (especially recently and why is that?), though previously there have been a number of CW's in wQBO years, notably in Dec1978, a key analog year. Interestingly the latest 30 hPa anomaly for the middle third of the month is starting to take the shape of previous years analogs - but I guess any possible lower split affecting 30 hpa may now put paid to that. Latest Analog If we get strong wave 1 activity following this wave 2, would you not suspect (assuming that the siberian side of the dipole is the strongest) that the possibilty exists that the Canadian vortex weaker segment could give way allowing a CW? All conjecture of course because we are a far way away from that at the moment!

I second what Tony says. Brilliant work Recretos. Here's hoping that we have a SSW to feed into the animator later this winter!

I think that we all know that the GFS isn't cannon fodder, but we also know Steve's thoughts on how it doesn't handle split jet flow when faced with a potential blocking scenario, so let's just leave it there.

If a wave pushes up from the trop, Nick, where is it most likely to be felt? Rather like the energy from an undersea earthquake being felt when and where the tsunami hits land - not just at its epicentre.

I'm loving this tiny cold European anomaly highlighted. Those in the surrounding warmer area can easily get there to get their fix of cold!

Long term (extending well into December) HLB's are probably not on the cards. However, even without the use of the GFS GLAAM pages which are not currently updating, we know that the lower strat is vulnerable to tropospheric wave action from possible MT's. There will come a point though when the strong upper vortex strat conditions will overwhelm the lower strat and any trop wave activity will be dampened considerably. In the meantime, though, I would not write off the longevity of any cold snap until we see firm evidence that the pressure on the lower vortex from the trop has eased off.

Hi Matt we have seen splits like this prior to the early winter cold spells in both 2009 and 2010. For the local trop induced wave split upwards into the lower strat is very favourable for producing significant cold in our neck of the woods. Here is 2009 strat link http://forum.netweather.tv/topic/57364-stratosphere-temperature-watch/?p=1625056 And 2010 (but with charts missing) http://forum.netweather.tv/topic/64621-stratosphere-temperature-watch/?p=1952060 We could see some interesting trop output. What a time for the ECM to upgrade its model especially wrt to strat input.

This is what we have been waiting to see - Guess when we have seen this before?

The energy has to go under - just look at the negative tilt of the Atlantic trough.

Extremely unlikely that a Scandi high would lead to severe cold at this jecture because we need the cold down from the arctic first. Compare the ECM OP anomaly at T+240 with that of its ensembles. Spot the difference anyone? Op Ens Seems to back up that GFS 50 hPa chart.