Reposted from the ENSO thread because this does have some significance on the prospects fro winter;

CFS is rapidly backtracking on its mega La Nina forecast.

http://www.cpc.ncep.noaa.gov/products/people/wwang/cfs_fcst/images3/nino34SSTMon.gif

In a week the ensemble mean has gone from dropping off the chart early in 2012 to bottoming out at -2.5. But most of the more recent member go for a peak of between -1.5 and -2.

I think it will continue to backtrack further over the next few weeks and the minimum will finish up somewhere around -1.

One interesting thing I'm noticing on the SST anomaly maps in the last couple of days is some warmer water just off the coast of Peru;

http://www.weather.unisys.com/surface/sst_anom.gif

http://www.osdpd.noaa.gov/data/sst/anomaly/2011/anomnight.10.27.2011.gif

Wonder if that could actually be the first signs of some ENSO warming into early 2012? Keeping in mind the Beijing model this month appeared to be forecasting an El Nino this winter. That seems outlandish, but perhaps it has picked up on some warming taking place through the winter?

Originally Posted by: Jay Lad 

Could I ask as a novice what affect/s this would have on the UK both short and long term.

Originally Posted by: WeatherExpert81 

Broadly, the weaker the La Nina the better the chance of a cold winter.

Originally Posted by: tallyho_83 

Gav - I thought it was Vice-versa re- La Nina!?

 

Meanwhile this is worth a read - similar to last year but a milder end to the winter!?

http://www.accuweather.com/blogs/news/story/56653/winter-forecast-europe.asp

Interesting given that this February was the warmest since 1998 and we had a warm end (March 2011) was very mild indeed. On 21st March I recorded 19C and some places 21C in London.

 

 

Originally Posted by: Gavin P 

Oh how lovely, another sh!tty winter is forecast, IMBY none of the previous 3 winters had any effect, typical 6 inches of snow.  

Originally Posted by: Gavin D 

Yes to be honest even last December really wasn't THAT bad if you compare to what Edmonton Canada on a similar latitude has EVERY winter. I think in North West England we recorded -16c in Dec which to most people in Edmonton is rather mild for a winter temp, they consider -25 and below cold, so we are very lucky in that we don't have temps that never get above 0c week in week out like Edmonton does and record -30s or -40s as minimums. It would take one heck of a climate shift for us to truly taste a sub arctic or extreme continental climate.

Originally Posted by: Gavin P 

Last December was the second coldest on record, several date records were broken,  Edinburgh experienced its deepest snow in 50 years while Sheffield recorded its deepest December snow ever. Are people really unsatisfied with last December simply because it was mild compared to an Edmonton winter?

The full list of ENSO tri monthly periods going back to 1950 can be seen here;

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf

Clearly weak La Nina coincides with cold winters more often than not, but there are exceptions. ENSO is just one piece of the puzzle, all be it an important one.

http://www.accuweather.com/blogs/news/story/56993/early-northeast-snowstorm-dest-1.asp 

Crazy really when back in 2005/06 parts of the NE States saw little snow and during the winter of 2006/07 Washington DC, Philadelphia, Baltimore, NYC and Boston didn't record their first snowfall until the end of January 2007.

We had a mild winter over here too!

I think 'weak' la nina now looks nailed - sub surface temps haven't cooled further - if anything they've warmed somewhat in the last few weeks, so I don't think it'll make a proper moderate event.  At its coolest we may make -1 on the tri-monthlies - so the CFS model ought to shift a lot over the next few weeks, and then it might finally produce a meaningful seasonal  outlook for the coming winter. 

From a coldie's perspective, I'm quite encouraged that the jet stream around the N Hemisphere looks rather prone to buckling still, so assuming this continues it ought to allow for some decent blocking at times during the winter months/

On the negative side, I don't really like the look of the current Atlantic SST profile with the warm anomaly still there to our SW.

I would appreciate a clarification, or expansion on what all these factors are that point to a mild winter because ther seem to be an equal number of obscure factors that others could point to to suggest a colder than average winter yet again.

http://www.osdpd.noaa.gov/data/sst/anomaly/2010/anomnight.10.28.2010.gif 

http://www.osdpd.noaa.gov/data/sst/anomaly/2009/anomnight.10.29.2009.gif 

The impact of SSTs is being overplayed. The MetO used to issue a winter NAO forecast based on May's SSTs, because this was the month where there was a correlation. I think the MetO have now ditched that technique (though I'm not sure) presumably because the skill level was low. If that's the case it suggests looking for pointers from the October SSTs doesn' have much value at all.

I've been looking at articles regarding the link between reduced Arctic sea ice and any link to the Arctic Oscillation. A study by Wang, J. et al (Feb 2005) looked into the hypothesis that, "Arctic sea-ice reduction trend in the last three decades amplified the quasi-decadal Arctic sea-ice oscillation (ASIO) due to a positive ice/ocean-albedo feedback." Their results support such a cause and effect having taken place. Apparently the effects have been noted since the 1960's with the ASIO being 'active' since the 1970s. As sea ice extent has been far lower in recent years than it was in the middle of the last century, I suppose the effect should be more prounounced nowadays.

So, following on from this, the question has to be: what does a more amplified ASIO mean in terms of winters in NW Europe?

Warmer seas in the middle latitudes of the North Atlantic will enhance the North-South thermal gradient and should therefore play a part in influencing storminess and tendency towards +NAO. They are only one factor of many, however, so our winter temperatures will not always correspond to what the Atlantic SST anomaly pattern suggests.

The jet stream represents the most intense horizontal thermal gradient in the atmopshere, which I imagine would tend to be near the greatest thermal gradient in the oceans. I'm not sure whether the SSTs are a cause of the jet stream positioning or a result of such... there could well be a big debate behind that one!

If you have a large pool of cold waters, the theory I've learnt suggests to me that higher pressure should be supported overhead, because the cold waters cool the air close to sea level relative to the air higher up, so resulting in less of a thermal gradient vertically within the atmosphere, which represents a more stable air column (as you get less in the way of warm bubbles of air rising and cooling with the resultant condensation of water vapour producing clouds). The sinking of cool air from high altitude will dominate over the rising of less cool air from close to the sea surface.

If that thinking is correct, then a pool of colder than average waters to our west and southwest supports more in the way of high pressure in those regions, which would bring a chilly but quite dry winter to the UK. That is not far from some of the long range forecasts out there at the moment.

UK Outlook for Monday 14 Nov 2011 to Monday 28 Nov 2011:

"Unsettled weather is likely to continue with a generally mild west to southwesterly winds for much of the period."

So where is the cold weather coming from?!

As far as I know the period mentioned by yourself is autumn.

I think it would tend to cause depressions to deepen in that region, and these would then swing NE - hence pumping up a ridge in the jet over W Europe.  I think though that the pattern ultimately kills itself, because the trough to the West should result in upwelling of cooler water - so the warm anomaly there gradually disintegrates.

I think when we've seen these persistent ridges in the jet over W Europe they can last 3-4 months (e.g. winter 88/89) - and we've had this thing since September now - so by that logic it may last a while longer yet.  I'm not writing the winter off though by any means - in fact I think it's beginning to look quite promising:

• Asian snow cover looks good - and decent southern cover over Tibet - idea being that the more southerly latitude cover will help reflect sunlight and boost ozone levels - could mean SSW events later in the winter. Good snow coverage should also help intensify Siberian High, which can help negative AO later on.
• Weak Easterly QBO - most v cold winters have occured with this setup
• Solar - still pretty weak, only one proper spot at the moment, lots of specs, very low solar wind considering we must be near max in the cycle. Expected sun spot count during winter (~60-70) combined with QBO, would be indicative of negative AO - although not as negative as the last few years.
• positive NAO during Oct - weak inverse relationship to winter NAO
• Persistently negative NAO over last few years
• Weak (rather than moderate) la nina looks on the cards now
• meriodinal jet stream pattern at the moment - although we have a persistent ridge across the UK.
• very dry continental Europe at the moment, should lead to rapid heat loss there shortly.

I fail to see, a clear signal for a mild winter this year. That does not mean I think a cold one is likely just that it's not set in concrete that the winter may be mild.

"... there is no signs for a rise in pressure to the NW of the UK across southern Greenland."

"...would bring... higher pressure to the NW...

I'm assuming this is just a slip or am I missing something?