Ok so I'm going to be doing a couple of posts on different aspects. In the ENSO thread here: http://www.boards.ie/vbulletin/showt...p?t=2057713492
, I've been discussing about Winter 2017/18 on what it could be like given the possible outcomes of ENSO.
I will go over what I have been talking 'bout since I made that thread in regards to Winter 2017/18. So yes, the topic of this post is ENSO.
Back in the Spring, it looked like we could have been heading into an El Nino event and quite a moderate one at that. Normally, a moderate El Nino is actually a very good sign for a cold Winter. Winter 2009/10 had a moderate El Nino - though there were plenty of other factors at play also. This is my reanalysis on historical moderate El Nino winters:
The reanalysis clearly showed a high chance of a cold Winter with a southerly tracking jet stream and very intense Northern Blocking as the winds go clockwise into an easterly direction.
As we eventually got past the Spring unpredictable barrier, the models were pointing more towards a weak El Nino and then ENSO neutral. I started looking at weak El Nino winters then, this is my reanalysis for them:
The reanalysis shows plenty of Northern Blocking but the jet stream is going through the country. This is very evident of Winter 2013/14 which had a similar chart. A weak El Nino is not a good sign at all for Winter. This was the trend on the models for a while then until late June and July. I decided to look at weak El Nino winters that were preceded by weak La Nina winters because as we know, Winter 2016/17 was a weak La Nina winter.
This was even worse than the previous weak El Nino chart as the jet stream is on a perfect westerly regime. With the very low heights and the intensified westerlies, it would be very stormy.
Fortunately, there was also the chance of ENSO neutral so I had a look at ENSO neutral winters that were preceded by weak La Nina winters.
This is the reanalysis of said winters.
It shows clearly Northern Blocking. It also shows a trough to the south with the winds coming in a clockwise direction from an easterly. This means it would be a rather unsettled but cold Winter. If the cold is intense then a very snowy Winter. This is a beautiful chart if that's the case.
The Pacific then started to significantly cool down during late June and July. As a result, the models reacted to this cooling and then started showing the possibility of a weak La Nina - once again for 2017/18. El Nino by this stage was dead and long gone.
I looked at the weak La Nina winters that were preceded by weak La Nina winters then. This is the reanalysis of said winters.
This was quite similar to the ENSO neutral chart but even better! It shows a very January 1982 or December 1995-esque kind of setup. This means extreme cold is possible - both months got down to -27c in Scotland.
What I think is the most possible outcome for ENSO is ENSO neutral. However, as can be seen from last year's extremely weak La Nina, a weak La Nina is certainly possible.
I will explain how similar 2012 is to the situation now in regards to ENSO in a post soon.