The Run Up To Winter 2011/2012- Signs Of A Cold/mild Winter And The Autumnal 'building Blocks'

[Snowmad79]

The past 8 days or more all the models have shown signs of building pressure all over the north tbh. But they have generally dropped that for a more robust high to our east. Consequently the 12z's Saturday evening have shown that to start decaying and I for one hope that continues.

[chionomaniac]

I'm not sure that anyone was 'staggeringly bullish' last Autumn - nobody - and I mean nobody - foresaw the early winter last year. I have seen plenty of 'staggering bullishness' before and much of it has been unfounded.

Today's update.

Yesterday, the T=240 forecast was suggesting some elongation of the stratospheric vortex at the 100 hPa level with the possibility of splitting. This remains the case today and interestingly this distortion of the vortex stretches right up to the top of the middle stratosphere. We have had a forecast of warming at the 10 hPa level which looks like occuring in the coming days without actually getting wrapped inside the vortex and it is probably this that is leading the change in stratospheric vortex profile. This can be seen quite clearly at the 10 hOa level on the ECM forecast.

The elongation is propagated right down to the 100 hPa level getting closer to the troposphere.

In fact at this level there is a suggestion of the vortex splitting but it is too early to say that this is going to occur.

The GFS is also suggesting a elongated vortex as the 30 hPA chart shows.

This type of event is always worth monitoring as a distorted vortex throughout the stratosphere will influence the tropospheric polar vortex positioning. It was the repeated splitting of the lower stratospheric vortex last year that led to polar air flooding southwards and northern blocking.

Cold spell on the way 10 days plus?

Well obviously I am not going to agree with you Ian!!

The cold spell last late November was well expected by some!!

[Weather-history]

Maybe an opportunity at least for England and Wales, to test out the warm(mild)/dry October-cold winter theory out again this time around. Depends on how much rain we get in the last few days but currently we are below average by a margin.

1978, 1985 and 1995 were Octobers that fell into this category and were followed by winters with cold wintry episodes, These are the examples that are generally quoted when this theory is mentioned and October 1981 is usually quoted as an exception.

The Octobers of 2005 and 2006 although warm were not dry and don't fall into this category.

I don't buy much into this theory, the figures since records began suggest not much correlation, its the fact that recent examples are given suggestion there maybe something to it.

Edited October 23, 2011 by Mr_Data

[Weather Boy]

Here's my totally unscientific, totally uneducated view on this topic.

I reckon that you can say that there are 'building blocks' but only with hindsight. You can look back after (say) a period like early winter a year ago and see that the evolution was putting the blocks in place. However, the reality is that the synoptics are never totally identical and it is never possible to predict exactly what they are going to do except in the short - medium term. So, as we know, after c. 10 days is FI and so one cannot make exact deductions beyond that kind of timeframe, although trends can be seen from the models and other tools like teleconnections.

The fact that we can't predict how these pressure systems, or buidling blocks behave, it must follow that there is no true thing such as building blocks because it is entirely possible that whilst these blocks could build to a cold or mild set up, it is at leat as possible to say that the blocks could be bashed down - so there are no real building blocks looked at at that point in time.

For the last 50-100 years, forecasters and staticians have tried to look for long term patterns and so far, have totally failed in terms of enabling set up to be predictative of future months. That must tell us that really, the building blocks thing doesn't really exist (or if it does, we haven't learnt about it yet).

[damianslaw]

Around this time in the autumn I look at how the jet interacts with heights to our NE. Late oct/early nov is traditionally a time when the atlantic stirs into fourth/fifth gear - a generally very quiet atlantic at this time of year is quite unusual, so i do sit up a little when this occurs. 2009 saw a strong block develop to our east around this time much we as we have now and we ended up with a atlantic stalling in situ to our west - last November was preety much the same and 2008 to a lesser degree.

[virtualsphere]

I remembered this discussion about a link between wet Novembers after November 2009 but before anyone knew what winter 2009-10 would turn out like. Took me a while to find it!

Mr_Data, on 01 December 2009 - 08:21 , said: Wettest Novembers on record for England and Wales

202.5 1852

200.8 1770

196.5 1940

195.9 1929

182.1 2000

182 ~ up to 29th November

In a pattern-seeking mood, is it perhaps significant that all the top four in that list were followed by, or had been preceded by (or both) an unusually cold winter month?

Feb 1853 CET 0.6

Jan 1771 CET 1.0; Mar 1770 2.5

Jan 1941 CET 0.5; Jan 1940 -1.4

Jan 1929 CET 1.3; Feb 1929 0.4

It's stretching things slightly to try and squeeze in the winters that followed Nov 1929 & Nov 2000, but each at least had a month decently below the mean - Feb 1930 (2.5) & Jan 2001 (3.2).

All in all, from those top 5, you can say that all were followed by winters with a cold - and often exceptionally cold - month.

Extending it to the top 20 (before 2009), most winters play ball with that hypothesis - but not those following the wet Novembers of 1970, 2002, 1926 (and possibly 1772 & 1836 - I don't know the means at the time).

Which you could say (if you were feeling optimistic) means that we have a 75% - 85% chance of at least one cold, or very cold month this winter!

If you think about it does make some sense, to get rainfall figures that high you tend to need a fairly southerly flowing jet stream and obviously if you carry that into the winter period then if you get northern blocking you've got the set-up there for a very lengthy cold spell. Of course doesn't always work like that but its an interesting link I suppose.

http://forum.netweat...4/page__st__340

Interestingly 1946 is high in the list of wet Novembers with 162.8mm, but 1962 is one of the driest. 2006 is also fairly high on the list so certainly not a guarantee of a cold winter month.

1946, 1978, 1985 and 1962 meanwhile are all in the top ten driest Octobers since 1910, which may help to support the dry October leading to a colder winter spell claim.

Off-topic, but another interesting feature about these statistics is that we've had five of the wettest months of the year since 2000: April 2000, June 2007, July 2009, October 2000 and November 2009, but we have to go back to 1991 to find our most recent driest month (May).

Rainfall data: http://www.metoffice...l/ranked/UK.txt

[summer blizzard]

Was August 1995 not the driest on record (the summer as a whole definitely was)?

[ZONE 51]

My first building block is the jet heading of south and or weakening, and watching the cold build to our north, with the atlantic shutting down, i also watch the snow build across europe, i believe this dips the AO, a scientist said this is what dipped the A0 so severe last winter-the snow cover, which then prolonged the cold.

[Snowmad79]

You need to look out for Higher than normal pressure over the poles rather than snow at lower lattitudes mate. If pressure is low over the pole its colder up there and its adds more westerlies to the circulation around the pole which then strengthens the Jet stream keeping cold locked away from lower lattitudes.

The models are progging LP to strengthen over the pole area which will only maintain a +AO and with it, the above is more likely.

[Snowmad79]

Similar theme on GFS 00z this morning with a bit of rain for all from today and into tuesday as a front sweeps up from SW to NE across the country. Wednesday onwards and out to FI looking largely dry as even though the ridge to our east/ Northeast is flattened out, HP still keeps influence over a large portion of the UK again, away from Western coasts and Ireland in particular where showers are still likely.

192 hrs (1st Nov) + sees the chance for the whole of country to see more in the way of rain as LP manages to make of an inroad.

I must say I like the GFS FI becuase, even though it wants to rebuild HP to east and north east again (though a bit futher east), it wants to keep the pool of HP over Greenland and later extend it over Iceland but also reintroduce HP over the pole. These are the things I'm going to be watching out for like a hawk over the next 5 weeks.

[Snowmad79]

Interesting to read the winter 2010/11 part 3 back again to see what peoples thoughts were this time last year:

Beng

I think we'll have a significant vortex this winter - but if it splits, or doesn't sit over Greenland, then it won't necessarily preclude a cold UK winter. At the moment, I can see a strong zonal flow across the Atlantic for a lot of the winter - but possibly on a very southerly jet stream - which could make things quite interesting and allow some blocking to develop at a higher enough latitude for battle ground warm/cold scenarios to play out.

Chionomanic 23-OCT-2010

I think that too. I am concerned that unless there is a SSW, we will see that the polar vortex will override other factors and I cannot see any prolonged cold spells. The best that I feel we will see is temporary mid Atlantic ridging into Greenland allowing northerly shots that will quickly topple. The other chance of cold from the east will depend upon the angulation of the jet. If we see early signs this winter that it is dropping south again and not angulated towards Scandinavia then we will have a shot, especially if the Siberian snow cover keeps increasing this Autumn.

So a strengthening of the PV, strengthend Jet and an atlantic outlook looked inevitable this time last year ALSO.

QBO is negative (easterly) atm looking at the monthly index (postive and remained so Aug 2010 to Aug 2011) and an article states this: "During negative (easterly) values of the QBO, low solar activity causes a negative Arctic Oscillation index and cold winters in North America, Europe and Russia".

Just goes to show we can't make any assumptions just yet, regardless of what the models and other signals say.

[Duane S.]

To be fair Beng wasn't a million miles off. We did indeed have a very southerly tracking jet that certainly contributed greatly to bringing us a lot of the snow we received, which he hinted at.

Also... as extraordinary as was early winter (and it certainly was), so was the end of winter very ordinary and mild. We had to endure a very strong polar vortex, no doubt thanks mainly to the stratosphere cooling rapidly from towards the end of December (I think it was) and staying that way before sharply warming too late on in the season.

I think there is a fair bit of doom and gloom because, for a while, November was looking like being comparatively blocked but, as others have alluded to, this is the time of year that this is least likely. The jet will likely always be at its most energized so cold/cool/mild winter on the way, a wet and windy spell during October/November will almost always have to be got through first!

[virtualsphere]

Was August 1995 not the driest on record (the summer as a whole definitely was)?

Interesting point - according to the MetOffice data, August 1947 beats it with 10.3mm compared to 17.8 in 1995:

http://www.metoffice.gov.uk/climate/uk/datasets/Rainfall/ranked/UK.txt

[mcweather]

To be fair Beng wasn't a million miles off. We did indeed have a very southerly tracking jet that certainly contributed greatly to bringing us a lot of the snow we received, which he hinted at.

Also... as extraordinary as was early winter (and it certainly was), so was the end of winter very ordinary and mild. We had to endure a very strong polar vortex, no doubt thanks mainly to the stratosphere cooling rapidly from towards the end of December (I think it was) and staying that way before sharply warming too late on in the season.

I think there is a fair bit of doom and gloom because, for a while, November was looking like being comparatively blocked but, as others have alluded to, this is the time of year that this is least likely. The jet will likely always be at its most energized so cold/cool/mild winter on the way, a wet and windy spell during October/November will almost always have to be got through first!

Couldn't agree more S4L. Both November 2009 and November 2010 were e wild and zonal before the cold set in.

[damianslaw]

Couldn't agree more S4L. Both November 2009 and November 2010 were e wild and zonal before the cold set in.

A 'blocked' November is highly unusual - don't think we have seen many of these in the past. Indeed even lengthy anticyclonic blocked periods are hard to come by in November. Some cold Novembers in the past such as 1988, 1985 and 1993 with lengthy dry blocked spells (eng and wales only) were followed by wet atlantic mild decembers. Perhaps the best synoptical pattern for November is a cool wet one with the atlantic ruling the roost but with a more southerly tracking jet - thus allowing higher than normal heights to set up across the poles indicative of a negative AO set up. Once these become very robust by Dec provided we maintain the southerly tracking jet then bingo we can pull down those northerly arctic blasts.

[Robbie Garrett]

I wonder?? That low would be very nasty if it dragged that cold air downwards! I've noticed with these models, they cannot for the love of life say if it's going to be a low or HP over the south of the UK!!!

Edited October 25, 2011 by Robbie Garrett

[Backtrack]

Unfortunately as per my forecast and indeed the models at the moment, I don't think we will see any sort of cold spell until the final stages of November.

[Snowstorm1]

Unfortunately as per my forecast and indeed the models at the moment, I don't think we will see any sort of cold spell until the final stages of November.

This is what I thought as well by end November I think we will be in a bitter freeze like last year in a way (could be wrong just a hunch) with by early/mid Nov signs will start to show this.

[Alex]

I remembered this discussion about a link between wet Novembers after November 2009 but before anyone knew what winter 2009-10 would turn out like. Took me a while to find it!

http://forum.netweat...4/page__st__340

Interestingly 1946 is high in the list of wet Novembers with 162.8mm, but 1962 is one of the driest. 2006 is also fairly high on the list so certainly not a guarantee of a cold winter month.

1946, 1978, 1985 and 1962 meanwhile are all in the top ten driest Octobers since 1910, which may help to support the dry October leading to a colder winter spell claim.

Off-topic, but another interesting feature about these statistics is that we've had five of the wettest months of the year since 2000: April 2000, June 2007, July 2009, October 2000 and November 2009, but we have to go back to 1991 to find our most recent driest month (May).

Rainfall data: http://www.metoffice...l/ranked/UK.txt

Was April 2007/2011 not both in the driest April months ever ?

[Liam J]

This is what I thought as well by end November I think we will be in a bitter freeze like last year in a way (could be wrong just a hunch) with by early/mid Nov signs will start to show this.

It's very likely anyone expecting a repeat of last November will be very disappointed.

Edited October 25, 2011 by Liam J

[Snowstorm1]

It's very likely anyone expecting a repeat of last November will be very disapointed.

Thats why I said in a way although I don't rule out the possibility

Edited October 25, 2011 by Snowstorm1

[Backtrack]

It's very likely anyone expecting a repeat of last November will be very disappointed.

It's not impossible, but it's also not impossible that we will never see a November like that again.

I think that most of out cold will be reserved for January & February this year, with November and December being write offs.

[Weather Boy]

When you say 'never see a November like that again' you have to think of the whole picture. Everyone on this thread (and indeed on this site as a whole probably) seems to associate last Nov with exceptionally cold snowy weather, but that was only the case in the second half of the month, and the only ice days (in my location at least) were well towards the end of the month. The first half was benign and normal with 17C being achieved quite widely in the month's opening days.

So, it was actually a very mixed month. It was exceptional, but not solely due to snow and ice.

[Backtrack]

When you say 'never see a November like that again' you have to think of the whole picture. Everyone on this thread (and indeed on this site as a whole probably) seems to associate last Nov with exceptionally cold snowy weather, but that was only the case in the second half of the month, and the only ice days (in my location at least) were well towards the end of the month. The first half was benign and normal with 17C being achieved quite widely in the month's opening days.

So, it was actually a very mixed month. It was exceptional, but not solely due to snow and ice.

But that's my point.

We started off warm in T-Shirt weather for some, and then we plummeted to the coldest second half of November on record (or something like that)

I mean, it's so unlikely we will see a contrast like that in November again!

[Liam J]

The signal for the early season cold and snowy spell last year was picked up in mid September, some 9-10 weeks in advance - just take a look back over the In depth/technical model discussion thread starting at page 21. Nothing to suggest anything similar on current guidance.

Edited October 25, 2011 by Liam J