Catacol

Good ECM op tonight - its out in FI anyway, but only a single day of average temps as the low fires through, and then back to cold by day 9. Ensembles likely to do the same. Looks like GP's assessment was spot on (again).

NAEFS ensemble data for T+180 shows clearly that heights are not going to be lowered behind this ejection of energy from Canada. The low may well punch through - though that is currently a long way from certain - and then heights swiftly build back behind. This is absolutely not zonal.

The voice of reason which perhaps a few might listen to. Overall pattern is blocked; the nova scotia low in the short term might lead to a temporary 48 hour blip, but otherwise a return to atlantic dominated weather is not going to happen - unless all the ensemble mean products and teleconnective signals suddenly go haywire... and I am yet ever to see that happen (though I guess there is a first time...) Battleground snow as both IanF and SteveM alluded to looks like the sensible call for next week once the cold has become established by the weekend. Dont even bother trying to work out where it might occur based on operational runs this far out - keep an eye on the means and then look to the high res operationals sub 72 hours once we get to next week.

Thanks - I assumed that once the date was updated that meant forecaster input had occurred. Best wait for the forecaster updated one today then, before getting bullish about a medium term blocked atlantic!

Dated 25th November.

Dont look at operational runs - check means. The runs you get on wetter or meteociel are only a single representation of 20 or more parallel runs of the model, and statistically the mean pressure patterns of the full suite of parallel options is the best to look at for trends. Interestingly it is true that the ECM means last night moved away a bit from polar heights and brought the vortex back together quite quickly, but if you pull up the ecm ensemble mean runs for midnight they have trended back to cold again. Gibby has mentioned the GFS ensembles in his post but not the ecm ones which is a bit odd. GFS ensembles last night were very cold; this morning not quite so much. The overall message here for you as a new learner is that the models are picking up on the overall trend for high lat blocking and cold weather, but are having one hell of a job resolving what is going to happen in the short term with the low pressure system strengthening over Nova Scotia. If that system fires through due east then it will upset the cold pattern for a day or two, but not for the long term ("game over") posts which some on here like to throw out. The only thing that would bring back the zonal express of west to east from here would be a strong reformation of the vortex. All the background signals are against that happening, so whether the nova scotia low upsets things a bit and brings westerlies in for 24 - 48 hours it will be only a blip in a trend towards blocked and cold. To get to the trends run the mean ensembles for several days - that gives you the picture and will help you ignore the odd operational run that goes astray, or even the odd ensemble run that moves away from the general direction. Only get concerned about a change of pattern if 2 or 3 ensemble means start to go the same way: that might mean something. As it stands at the moment this has not happened - at least for the long term. I posted the 5 day cfs mean chart earlier - here is the slightly longer range one - there is nothing remotely zonal or mild on the horizon from this up to date mean analysis. In fact this is reverse zonality at its best!

For all those panicking this morning take a look at the 6 - 10 cpc product today - anything remotely zonal there? Nuff said.

When does the Baltic begin to freeze?

Yes... for once today we had an ensemble mean from ECM that wasnt really worth looking at from the moment it fired up the vortex and lowered polar heights. Just shows that an operational run is thin evidence of anything, and a single ensemble run is not a whole lot thicker. Trend spotting is about a sequence of ensemble runs coming together... just as JH and GP tout.

Just noticed the date on the bottom. Interestingly on the cpc website it clearly says updated 25th November. Bit odd that...

... I would add that the CPC update today is this: Notice the very strong heights retained at the pole, and substantially low pressure predictions over Europe. The ECM run at present has the Azores high regaining strength and a flat pattern dominating to the north, this within the context of collapsing polar heights. It just doesnt fit. Something is wrong there. EDIT: to be fair ECM at 240 is not flat at all. The pattern is still very blocked and meridional... so it has not lost total sight of the cpc predicition... but its modelling of the low pressure exiting Canada in midweek seems very aggressive. I suggest that it is putting too much energy into this, and that tomorrow it will pick up on this and reverse the ensemble picture of today. We will see.

I tend not to bother to look at operational runs at all anymore - they are a waste of time for accurate trends beyond 96/120 hours, but one observation from the ECM ensembles tonight is that they seem to indicate quite a swift reforming of the vortex after 120h with polar heights collapsing. I do not have GP's knowledge at all - but my understanding of the background signals is that this is unlikely, with the vortex under quite severe pressure. This is rather at odds with the GFS ensembles that maintain higher pressure over the pole and a split vortex. I think discussions of a short wave flattening out the atlantic pattern are a bit of a red herring therefore. They mask the fact that if the ECM is modelling the polar heights incorrectly then the zonal solution offered by the operational run tonight simply wont happen. The question therefore becomes: why is the ECM lowering polar heights and reforming the vortex when teleconnections say no, and the GFS ensembles say no too. I dont have the answer to this - GP is certain to know better than me... but it makes me rather dubious of the ECM solution at present. An even bigger question would be whether any of these models have a proper grasp of stratospheric factors. We know that the UKMO now incorporates these into its thinking, and they are staying with a blocked atlantic. At present, therefore, I am not too worried by the ECM flip, though I would be very glad if the more knowledgeable posters on here could provide a more hemispheric analysis and offer a reason why the ECM ensembles are lowering polar heights and reforming the vortex within the next 10 days. Is it just off on one?

I'll tell you what: 1. These are some of the best ensemble charts in the semi reliable frame that we have had for snow in a long time, comparable with Dec '10. 2. The current longer range teleconnections for winter are possibly the best we have had since internet weather watching came into being. When GP starts talking of a distressed vortex into January, with "interesting" consequences, we should all know that something is afoot. 3. The MetO longer range forecast mentions "cold" and "snow" - and they choose their words very carefully. This now takes us out to Xmas Eve. 4. For those who had to endure the winters of the late 90s and early 00s everything at the moment is eye candy of the best sort. 5. Today is November 24th. The fact that 611 people are on this thread as I type - and winter hasnt even started yet - is extraordinary and exciting. 14 weeks of full on winter is still in the near future! Conclusion? Chill out. Take the wise advice and stop jumping on top of every operational run and look at ensemble mean charts and read the wise words of wise old heads. Cold is coming; some people will get snow. We will all get frost... and the outlook is excellent. When GP finally releases his full winter forecast (and if you are new to this then trust in the fact that he has a very very good trend record for winter forecasting) then hopefully we can all get even more excited. Most of us know that in pattern change scenarios where blocking is on the cards the models have a poor record, and cant be trusted beyond 120h - maybe even past 72h - so keep some perspective. However I must admit I am more excited at the overall prospects for this winter than I have been since joining the weather community over at TWO many years ago. Flooding down here is awful at the moment, but even that fills me with winter excitement because with the jet so frequently south these days it increases the chances of the battleground scenario snow that is best for many of us away from the east coast or the highlands. The ensemble means are screaming of battleground snow potential for the first week of December at least. Fantastic.

When is GP's forecast coming out? I am getting impatient...

You are right. It is disastrous down here: and heavy rain this weekend could really bring this region to a halt. I have never seen rainfall like it in such a relatively short space of time. Back in 1999 (I think) the local paper famously reported that we had had 100 days of consecutive rain over the autumn season, but much of it was light or on and off, and while the ground did become saturated we didnt quite have the flooding we have now. We have the local canal collapsed, roads sliding away, main arteries paralysed by feet of water, power lines down, trees falling and causing damage, events cancelled... the list goes on. Not good at all.

I know someone whose wife is quite big at the MetO and apparently all the main forecasters are away next week at a conference. We may well see a rather "lighter" than average week from them while these folk are away!

I used to live in Bovet. Happy days... :-)

Still raining. I make it 1 hour and 20mins of either very heavy or moderate rain now without a break on top of showers earlier. I dont know what the rainfall total is so far - doesnt really matter: the ground wont cope with the speed of what has fallen so I am expecting to hear of transport chaos. In fact I have already met one lad up here who cant get home tonight...

Following about 25mins of driving, lashing soaking rain we now have a steady moderate soaking going on... enough to keep the lake outside my house expanding slowly. I'll bet my bottom dollar that the A38 to Taunton will be closed again, and the river Tone very close to bursting its banks.

A monsoon just hit Wellington - the road and driveway outside my house is a lake, and it is still hammering down. So far 15mins - I would imagine it has been enough already to close all the local roads that were closed yesterday. Flooding is going to be widespread again.

Hideous here this morning. Motorway closed, schools closed, traffic backed up all over the place. Local weather station has recorded 41mm rain in the last 8 hours.

Ah - thank you. I think I understand this - use of the word "ridge" in your previous post had me a bit confused with the vortex diagram compared to what I was expecting to hear based on recent comments. Do I assume then that tropospheric wavelengths tend to shorten as winter moves forward? A vortex displaced to Greenland/Svaalbard combined with tropospheric blocking underneath in the same region has my head spinning a bit. That sounds like a potential setup for a recurrent pattern of northerlies and occasional easterlies through Dec/Jan as we sit in the eddy of that blocking canadian/greenland high, with Feb a 50/50 month alternating between siberian driven easterlies and occasional mild south westerlies. This assumes the warming over Canada that you are hinting at. I am a self confessed novice, but I am starting to wonder if we are on course for the coldest overall winter in a while. Coldest since 95/96? Maybe colder?

An increasingly west based NAO then come Feb? Hmmm - best hope for some intrusion from the Beast then... On a "help me" please note GP - you said in an earlier post that a west based NAO was not a problem in Dec but could be a problem in Feb. I understand the potential synoptics of a western based NAO but am a bit puzzled by the month vs month distinction. Can you elaborate a bit?

A little bit of stat research on these analogue years GP has identified. DJF Cets of those analogue years: 1970: 3.30 1983: 4.27 1996: 3.03 2003: 4.70 2009: 3.53 Looking at them overall a below average set of winters this with the exception of 2003. The 1960 - 2010 CET winter average Dec - Feb is about 4.28. In all bar 2009 there is a trend for winter to get colder as it progresses though it is worth recognising that only 2 really "mild" months are present in any of these winters: Jan 83 which was the second warmest since 1960 and Dec 2002. These 2 mild months had a big bearing on the overall Cet of the years as listed above. 3 out of the 5 had Feb Cets of sub 3 degrees. Of the total of 15 winter months here 11 of them fall below the 1960 - 2010 average. My conclusion? I am not really a stats man, but having taken a look at the figures I am now putting a small wager on GP going for a cold winter, perhaps an overall CET of around 3.5 with an overall shape to it of a coldish December, a slightly milder January and then a potentially bone chilling February. I might get time later to take a look at Dec 02 and Jan 83 to see just why they were so mild. I am not skilled enough to be able to imprint any of the current ENSO/QBO/Solar/SST factors on top of this analogue, though I await GP's info on all this with real excitement. EDIT: Jan 83 was a horrible month: high pressure in charge to the south throwing warm air at the UK with low pressure running west to east throughout. Yuck. Dec 2002 much more interesting: a really "nearly" month with blocking to the east and a good number of days under an easterly. Last 10 days saw the mild win out, and the overall monthly temp rather skewed after a pretty cold first 20 days or so.

Ah - ok... but are you so sure that the trend for blocking will be east to west rather than a ridge coming out of the US or perhaps even sourced from the Azores? There does indeed seem to be consistency now for this blocking episode to occur but at this time of year I think a 1% rating of a greenland high forming not from a retrogressing scandy high is a very brave call. The form horse for me would be a rise in pressure from the west. I am wrestling to get the concept of increasing angular momentum into my head properly, but if I understand it correctly the increased forcing of energy towards the poles ought to help force the pattern forward a bit, and hence I cant quite see how a scandy high will retrogress given GP's post yesterday which pointed to an increase in momentum that went off the top of the graph. A scandy high might well win the race to form first, but I cant see it retrogressing as you are suggesting. Only chance? I think you do enjoy a bit of hyperbole :-)