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Steve Murr

Winter 07/08 A half time round up

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Good afternoon Folks!!--

So, as we pass the halfway line of another Winter its worth reviewing whats been happening across the UK & indeed globally in terms of witnessing Seasonal conditions-

La Nina-

Whilst there are unconfirmed links with the UK's winter type pattern in la nina its worth re-analysing the type of global pattern seen in the La nina events of the past-

Looking at the NOAA dataset-

http://www.cpc.ncep.noaa.gov/products/anal...ensoyears.shtml

& Going along the lines that the ensemble mean of La nina forecasting suggests that the overall strength of this mode will not moderate until past Winters end- averaging around 1.3-1.6

post-1235-1200585286_thumb.png

Then the following 7 years come into view-

1950,1971, 1974, 1976, 1989, 1999, 2000

The simple re-analised forecast just based on the La nina mode would have been a strong polar vortex lodged over Greenland & a dominent Westerly flow-

post-1235-1200585857_thumb.png

Compared with the ACTUAL observed December profile-

post-1235-1200586725_thumb.png

We see that the profile over Greenland is VERY similar, however blocking to the EAST is more significant- Incidientally this is inline with Strong Easterly QBO years-- & where the analogues above arent as quite as robust as this current pattern-

Also to consider we have the stratospheric temp profiles- The monitoring of the Stratosphere however, did not start to be documented until 1978 so we only have a 3 data set-

1989,1999 & 2000-

Clearly out in front in terms of polar temps is Winter 1999/00- ( end 99 into 2000)

post-1235-1200587488_thumb.png

However its still not as cold as the Current Profile of Dec 07 & Jan 08-

post-1235-1200587686_thumb.png 07- Look at Dec

post-1235-1200587743_thumb.png Jan 08- Very :rolleyes:

To summarise what the atmosphere is doing in these Cold stratosphere years, STRONG La nina Winters is fairly straight forward-

The Global circulation cells ( polar, ferrel & hadley) responde to local forcings which enable them to become either stronger or weaker in terms of expansion / contraction against the other cells-

The way to view the forcings 'perhaps' going forward is for some sort of 'net effect' for each cell & how this will effetcs its behaviour-

( Heres a link to assist if its your unclear around these global dynamics

http://www.atmosphere.mpg.de/enid/3sj.html

The polar cell is the easiest to determine because the Atmospheric forcings only generally come from the Cryosphere at the surface & the stratosphere above-

For example, research on the polar Stratosphere leads us to believe that a COLD stratosphere leads us to this simpified equation-

Cold & or colder than normal Stratosphere >> Forces a Faster & tighter Circumpolar vortex over the Pole >> this drives a greater Easterly momentum in the jet Stream & pulls the jet core closer to the pole

The effect of the cryosphere I would suspect is less pronounced, but the assumptions made are that the wider expanse of Cryospheric conditions at the pole & over the Large continental land masses create a feedback to assist a SLOWER circumpolar vortex-

With these 2 variables in mind the polar cell this Winter to date 'OVERALL' has behaved as expected inline with natural forcings forcings applied-

The mid lattitude cell ( Ferrell) has the greatest of expanse of variability crossing oceans & landmasses, however when we look at net effects of forcings on this Cell & the subsequent battle against the polar cell we cover a multitude of 'local' factors-- which is why Winter forecasting along 40-50N at a regional scale becomes very difficult-

Taking La nina for example the net forcing in the Nino regions will be largly amplified in comparison with its effects across a continent thousands of miles away- because however it starts in the Pacific & because its a LARGE scale forcing as opposed to smaller Atlantic ocean dipoles or tripoles it cannot be written out of the equation-

At this point to be apply to rationalise ALL the forcings of the mid lattitudes as an equation or more importantly define them as a +VE or -VE forcing on the cells Expansion capabilities as above both my level of skill & indeed pretty much anyones--- This being the key to an accurate Winter forecast-

Importantly though, whilst this lack of information cannot produce a forecast it can certainly produce a hindcast with an analysis of the location of the polar front over a month or season & what that means to the region your forecasting for-

Remember the polar front is generally located within 35N to 50N- in Stronger Polar cell years it moves South- in Stronger ferrell cell years it moves North-

So what then for 07/08 as a Winter-

In reality as a pro forecaster or even as a keen amateur all you need is a MEAN average for the location of the jet along a point & the information on how thats behaving- & here we have that data on a Daily basis, Weekly & a monthly--

MEAN & ANOMALY PLOT-

Heres the Link:- http://www.cdc.noaa.gov/map/clim/glbcir.shtml

Use 250MB Zonal wind speeds-

Sadly i havent got the 30 day anomaly & mean plot for Dec-- However look at the attachment- Look at the TOP graph as it shows the Climatology mean ( 1985-95)

post-1235-1200590876_thumb.png

The peak of the jet is around 31N & this locale is important because when we get the 90 day chart which covers Winter then that lattitude is the MEAN for WINTER- 7 can be used as a benchmark for current jet movement trends-.......

Anyway the top graph shows 31N, the graph below shows ANOMALIES over the 30 day period along the lattitudes- the key is to see where the Peaks & troughs move along 30-40 N-

IF the Peaks are moving from 31N to the RIGHT the jet core is faster and more importantly further NORTH towards the POLE

Further South & the jet core is moving South-

Obviously the im

age above broadbrushes the mid lattitude as a whole & NOT ONLY Europe, however this is a good marker on the AO & crucially a good marker for trending climatology in terms of long term means-

If we do start to see a change propergating down from the pole in the mean locale of the jet then this will be refected in the 1 & 7 days means around the pole & mid latts-

http://www.cdc.noaa.gov/map/images/fnl/250uwnd_07b.fnl.html

The rest of the Winter 07/08 hinges around the continued drive of the Polar Vortex, to get any sniff of cold from the East or North ( that lasts more than one day) the Stratosphere needs to warm up as fast as possible OR there needs to be a rapid weakening of the La nina mode-

Well the La Nina isnt going to change anytime soon because the Surface temps of the seas are driven by the subsurface motion of the sea as these propergate upwards & these just dont change that fast-

On the other hand the stratosphere can change as if someone turned a gas burner on-

The ECMWF forecasts & monitoring of the stratosphere have started to shed light on events over the next 8 days in the stratosphere & can be found here-

http://strat-www.met.fu-berlin.de/cgi-bin/...mps&alert=1

post-1235-1200592050_thumb.png

This type of even can can classed as a MAJOR warming event-

it shows then on the NOAA stratospheric warming anomalies as something like this-

http://www.cpc.ncep.noaa.gov/products/stra...ALL_NH_1985.gif

Notice the properagtion time of Warming in the stratosphere takes around 21-28 days to move to the surface-

Based LOOSE on the current ECMWF forecast which is +8 takes us out to 25 Jan-- then manifestation +21 takes us out towards Valentines day for the chances of Winter to finally rear its head- in terms of available blocking at HIGH lattitudes- this does not of course rule out a lucky hit for the UK from a mid lattitude high-

Summary for Winter 07/08 in terms of Averages--

December-- Polar front & Jet core MUCH further north as shown by the zonal wind anomalies to the North of us-Note Scandi

post-1235-1200592687_thumb.png

The Uk managing to get slightly below average from being in the SW quadrant of the Quasi stationary high to the NW- ( rememebr we were stilll south side of the PF)

January-- No change to Decembers Profile in terms of the jet without the blocking to the East-- THis means the penetrationj of warmer air will extend furtehr into Europe-

NW europe is VERY +VE for surface temps-

look at the surface temps for the last 7 days-

http://www.cdc.noaa.gov/map/images/fnl/sfc...er_07b.fnl.html

notice the slice of colder air has gone WAY back East..

Febuary....????????

Major stratospheric warming to develop at the end of Jan to properagte towards mid Feb giving the 40n Lattitudes a chance of proper Atric cold outbreaks-

Overall a well above average Winter-....

Finally the topic of the UK winters getting sustained Cold from the East & North East being a thing of the past does has some merit-

To get the Cold to back west from the low Countries all the way to the UK we need a SLOWER than Normal jet through the Svalbard Corridoor -

Think about it, to get the cold here the jet has to be slow enough to buckle be able to move back West underneath the a developing high-

The faster the jet is-the further east the jet Goes before starting bend & return back South west, also that limits the scope for how far it can then return west-

THis means the marginals of cold air from Central Europe move back east & rather than the boundry often being to the west of the UK it now possibly sits towards somewhere towards Holland ( Note to self DE BILT ENSEMBLES WILL BECOME less representative with time)-

To demonstrate this problem I re-analised the Zonal wind speed anomalies from 1997 to date- this is 10 year running mean-

post-1235-1200593495_thumb.png

Remember for 10 years the anomalies 'SHOULD' be fairly low-- however whats VERY striking is the pacific jet stream pattern beoming further north & Stronger-

But also the small patch of green through Svalbard & over the top of Scandi indicating a faster flow' over the top' in this region- this is a problem 2 fold-

1) it highlights the plight of our Easterlies quite well

2) demonstrates that the orientation of the anomaly is more skewwed West/East showing that the jet is flowing faster- not allowing polar air to filter South out of the pole-

In summary then... End of this Winter is the only chance we have of proper cold & from reviewing the historic stats Winter is being Squeezed from the warmer seasons especially at the Autumn side-

Also Easterlies-- thats the ones that have the residents of NW & TWO salivate over could well be a thing of the past- maybe not in absolute terms but in terms of statistical averages V the Norm...

S

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Very interesting Steve.

A good read which isn't too hard to understand.

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Good read as always Steve

With La Nina due to start decaying at the end of winter and the full effects of the stratospheric warming event possibly not being felt until near the end of February, do you see a cold March (rather like 2005 and 2006) - is the QBO still favourable then?

PS - you may be a year ahead of yourself in the title of the thread

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Good read as always Steve

With La Nina due to start decaying at the end of winter and the full effects of the stratospheric warming event possibly not being felt until near the end of February, do you see a cold March (rather like 2005 and 2006) - is the QBO still favourable then?

PS - you may be a year ahead of yourself in the title of the thread

Yes end of Feb/ march is a good prospect....- The weaker the better-

Yes the title is out by a year :rolleyes:

Can the Kind mod that edited the original post edit the title..?? :)

S

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It really does sound bad news and that Winter 2007-08 could well and truly be over.

Still, nevertheless February may still bring some cold weather to the UK. February is a month that tends to bring a less intense polar vortex than earlier in the winter, largely due to the stratosphere reaching its coldest point of the year on average during December. It does explain to me well that it is very difficult for northern blocking to become established at high latitudes to give the UK a chance for cold when there is much cooler than average temps in the stratosphere. What I cannot understand is why we still cannot get cold zonality like January 1984 etc (NW-SE tracking depressions) with a cold stratosphere.

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What I cannot understand is why we still cannot get cold zonality like January 1984 etc (NW-SE tracking depressions) with a cold stratosphere.

This is the coldest sustained spell of zonality that I have seen since the 80s - certainly has broken the pattern of say since 1998 when the bartlett/eurotrash high always seemed to be in situ.

I don't think we can write winter off just yet - March (especially the first half) is usually a more wintry month than December and this is more true in recent times. So there is still around 2 months of 'game on' yet. I can however see why people would be frustrated with the January pattern which is another thing feature of recent winters

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I was thinking we might get a cold March leading to a cold spring. It'll take a month or so for the weather to follow the weaker La Nina and so forth.

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Some more great analysis in there Steve: the 250mb reanalysis is quite telling, not only for the incerased activity in the Pacific, which you highlight, but also for the increases in energy, albeit slight, to our E, which as you continue to suggest, reduce significantly prospects for blocking close by that is consistent with much of the sort of sustained cold that occasionally used to visit these shores.

I also agree that the best shout for cold in the even larger teapot is later on; it's certainly been the case in several recent years, though this year I did rather favour a cooler January myself.

My only quibble with your thread is the suggestion that we're past mid-winter: astronomically we are, and in old fashioned winter terms we would be encroaching upon that point. In the even larger teapot though I think we're only just entering the window in which wintry weather can reasonably be expected.

...

I don't think we can write winter off just yet - March (especially the first half) is usually a more wintry month than December and this is more true in recent times. So there is still around 2 months of 'game on' yet. I can however see why people would be frustrated with the January pattern which is another thing feature of recent winters

Agreed

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In the even larger teapot though I think we're only just entering the window in which wintry weather can reasonably be expected.

Would agree with that (except the use of the word 'modern') - with a caveat that we seem to get an unusual snow event in late November / early December every other year or so.

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Thanks Steve for taking the time and effort to explain some of the factors that affect our Winter.

I wondered why we got no High pressure further North earlier this month when we had the jet so far South for a while.

Is this simply because of the very cold stratosphere over the pole?

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It does look from those ENSO ensembles that La Nina is likely to persist for the rest of 2008, and through this summer. What does this mean the summer is likely to bring? Very difficult to say, as SSTs play a big part in summer synoptics as well as ENSO conditions. As we are in a similar ENSO state to 1999 and 2000 personally I'd favour a summer similar to those years as a likely outcome.

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As we are in a similar ENSO state to 1999 and 2000 personally I'd favour a summer similar to those years as a likely outcome.

A cursory glance shows 99 - Cold June/Mild July and the opposite for 2000 with August around average, so no real pattern there.

Wonderful info and summary Steve.

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My only quibble with your thread is the suggestion that we're past mid-winter: astronomically we are, and in old fashioned winter terms we would be encroaching upon that point. In the even larger teapot though I think we're only just entering the window in which wintry weather can reasonably be expected.

Yep- I know-- I was inferring on what people normally perceive winter to be-

At an extreme note -- you could say our current Winter with a slight Climatological adjustment has only 8 weeks of proper potential--

2 jan, 2 March & 4 feb...

S

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Excellent post Steve.

Couple of things that strike me:

The overall z500 pressure anomaly is reasonably consistent with a Nina pattern over the Pacific and North America, slightly flatter than perhaps anticipated from the SSTA reanalysis:

In the Atlantic, the Nina pattern is less obvious with a pronounced -ve height anomaly south of Greenland and Scandinavian block.

One of the odities about this Nina is the quite active tropical forcing alongside the -ve ENSO state, something we don't often see as the two would generally be assumed to cancel each other. This has lead to two pronounced upward spikes in the GLAAM, both of which have been associated with an increase in zonal winds across the Pacific and Atlantic:

http://www.cdc.noaa.gov/map/images/aam/glaam.gif

The amount of tropical forcing has been evident with two the MJO successfully completing two circuits - quite exceptional for a -QBO / Nina year.

http://www.bom.gov.au/bmrc/clfor/cfstaff/m....Last90days.gif

I think this, and the Atlantic SSTA, has trended for a Scandinavian / UK block pattern.

With a fading easterly QBO and tropical forcing, this takes us to a point where the polar stratosphere should have detonated (nearly all MWWs were within this parameter). It plainly has not. Not yet.

For the record, the AO is currently about +0.2, probably edging towards +0.5 by the end of the month on daily averages. Not as negative as anticipated and the well-documented coolness of the polar stratosphere is having a tangible impact on the polar field right now. December's +AO was attributable to other factors however - a possible pointer for future years when we enter with a record low level of snow and ice cover.

http://www.cpc.ncep.noaa.gov/products/prec...ily.index.ascii

Question is, why was the stratosphere so cold in December ? My hunch at this stage is the failure of planetary and Rossby waves to penetrate the polar vortex due to some interference by the largely east based Nina which prevented the necessary development of a storm system over the mountains throwing out waves towards the pole. It's no coincidence that we see projected warming following a massive mountain torque event just after New Year:

http://www.cdc.noaa.gov/map/images/reanaly...ltaum.90day.gif

This type of event is more a feature of Nino winters so there may be a case for Nina winters to feature less poleward projection of waves and consequently a cooler stratosphere.

Reanalysis of the polar cross sections for the Nina years selected above...

Reveals some similarity with the story so far....

What lies in store for the rest of the winter ? Well, two important factors here:

1) The Nina is now West-based (greater anomalies in ENSO regions 3.4 / 4 compared to 1 and 2).

http://www.cdc.noaa.gov/map/images/sst/sst.anom.gif

http://www.bom.gov.au/climate/enso/indices.shtml

This has important implications for the placement of Pacific anticyclones and overall circulation pattern as it will trend the ridges further westward - drawing any mid latitude high back towards the west of the UK.

With the ridge over the NE Pacific retrogressing, this opens the door for further storm systems to crash into the Rockies putting pressure on the polar vortex, possibly setting up a second warming event into February. We do not know where the current event will end up although it is a good signal for an overall return to neutral - negative AO values at least removing any tendency for the winter to finish with a warm flourish. If it does develop into a full blown event, suddenly all bad memories of the winter so far will fade very quickly.

Overall, the state of play - most of the UK between +1 and +0.6C with some notable warmth over Northern Europe and coolness further south.

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Really informative posts, certainly makes the old grey matter work overtime, thanks for all your hard work. :doh:

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Thanks GP for your post too.A lot to consider and absorb but educational.Much more to take in these days compared to my youth,when all i had was the sypnotic charts off the tv and some newspapers.

I do appreciate what yourself,Steve,Brick and all the knowledgable members of the forum post.

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GP, I read on TWO (Gavin P might be able to find it) that there is a study into why the Polar Vortex has been stronger over recent years and it says it's due to the number of CFC's in the air which increases the cold more significantly than previously. Might be worth checking out, it might have your answer!

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Great analysis Steve, I have gathered enough from your explanation there, that it is becoming increasingly difficult for winters in the UK to see any sustained cold from the east or north in the depth of winter.

A very bleak and sobering awakening indeed, although I think many of us know deep down that we will never see the likes of 62-63 / Jan 87 / 78 / 79 etc. again in our life time, unless of course we are prepared to move to eastern Europe or Canada, oh for a repeat of these synoptics Jan 2nd 1963. An easterly from the depths of Russia to Canada, never again I fear. :D

Paul

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I've thought for a while now that the best we can realistically hope for is something like 1995 but even that is becoming increasingly unlikely. Maybe 2001 is more likely.

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Thanks GP for another very informative post, a few straws to grasp from your analysis. So possibly there will just be enough of winter left for us see something worth while before solar energy increases and extinguishes all hopes for 2007 / 2008.

Fingers crossed.

Paul

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Remember for 10 years the anomalies 'SHOULD' be fairly low-- however whats VERY striking is the pacific jet stream pattern beoming further north & Stronger-

S

Apologies if someone's already mentioned this, but aside from human induced climate change, could the shift in the pacific jet have been a result of the warm phase of the PDO? Weren't easterlies quite rare in the last warm PDO episode at the start of the last century too - maybe a small straw to clutch at anyway given the PDO should be due to switch soon (and is in the cold phase this winter - not that it's helped us this year of course!).

To the north of Scandinavia we have seen a big reduction in the average sea ice extent in recent winters - which again could be influencing the jet in that region, but I couldn't give a good reason for this to reverse unless we see a sustained spell of negative enso conditions allowing some global cooling.

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Well if its winter half time id say a slice of orange[old half time footie fare] and a rousing team talk from Kevin Keegan is required,here in the snowless triangle,we greet a single snowflake like a goal at St.James park.how desperate is that.Into the second half have got Channel Low off the bench,played up front with Polar low hoping for our first snow home win since 28 1 2004 the crowds gone wild.

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It not looking good! My kids think I am mad when I tell them about the snow we used to see, frosts all day, fog for days on end. All they get is the odd dusting of snow each year! Still it seems enough for them to have a day off!

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