Correlation between ENSO and Irish Weather

There has not really been any confirmed information on the correlation between ENSO and Ireland's weather conditions for a simple reason. That simple reason being exceptions. When making up a theory about ENSO, you will most likely always find an exception (as you do with just about every theory in Ireland's weather :rolleyes:). For example, there's the theory that if a moderate El Nino does take place, it means a cold Winter is coming. Incorrect, a moderate El Nino just gives the increased chance of a cold Winter, not a guarantee. Like, a moderate El Nino helped bring a cold Winter in 2009/10 but a moderate El Nino also took place during the mild Winter of 2002/03 which had all three Winter months milder than average.

Yes, El Ninos and La Ninas can cause stronger jet streams but really depending on the strength of the ENSO event. Remember that Cumbria recorded 3 of its worst floods in history during 3 El Nino events (11 January 2005, 18/19 November 2009 and 5 December 2015). It's interesting how coincidental that is and the fact that each of these El Nino events were of different strength, the 2005 one being weak, the 2009 one being moderate and the 2015 one being very strong. The south of Ireland suffered through the extreme rainfall of the 3-6 August 1997 during the very strong El Nino that was forming. Many of the most extreme rainfall events tend to happen at the time of an El Nino, like all these very wet events took place during an El Nino along with the ones mentioned:

5 August 1986
25 August 1986
14 October 1987 (and the Great Storm of 1987 I might add)
Winter 1994/95
20 October 2002
14 November 2002
27/28 October 2004
Winter 2015/16 (as a whole)

Perhaps it's just coincidence? La Nina events can also cause such extreme rainfall events but rarer than El Nino events. The 5 November 2000 Dublin floods took place during the weak La Nina of 2000/01.

Neutral ENSO can lead to blocking along with a moderate El Nino but that does not guarantee cold winters by any stretch of the imagination. Winter 2013/14 was a great example.

In Winter 2013/14, high pressure was very dominant over the Arctic and therefore, the Arctic Oscillation (AO) was significantly negative. Yet, the jet stream was very powerful and a trough/storm path stretched from midwestern Canada all the way to the southwest of Norway which included us. See for yourself in this pressure reanalysis from NOAA for Winter 2013/14:



Thunderstorm days are definitely more common during ENSO neutral, you're right about that. The most severe thunderstorm in modern times that people can remember in Ireland is the 26 July 1985 thunderstorm that took place in Dublin following the weak La Nina Winter of 1984/85. By the time, July came around, Ireland was in ENSO conditions. A strong La Nina is a good sign for a very blocked Summer with plenty of high pressure. Two of the best summers on record followed a strong La Nina Winter (1976 and 1989 being the summers). Here is a pressure reanalysis of the summers that followed strong La Nina winters. Yes, there seriously has not been a strong La Nina since 1988/89 but there hasn't been a strong El Nino since 1972/73.



We do get dry days to compensate for the wet days. Once you look at it carefully, we indeed do. After an unsettled Summer in 2015, we got a very dry October and reasonably dry September (despite the very wet days of the 11th, 13th and 21st... much of the month was very dry). We got compensated then for an exceptionally wet November and Winter. Spring started off fine in March with a long dry spell mid-month then April was very wet in parts whilst dry in others. May was variable also but dry for the most part. Summer in parts was wet whilst July was dry in the east. The mostly wet start to 2016 up to this point was washed away by the significantly dry end to 2016. October was the driest since 2007, November was the driest since 1988 and December was the driest since 2010. January continued the dry spell to compensate for the very wet Winter of 2015/16. February then brought a wetter interlude along with March but April so far has been very dry to compensate for this. It's the same with cold and warm months. The 2000s had a very high quantity of warmer than normal months but lack of colder than normal months. The 2010s has had a higher quantity of colder than normal months whilst warmer than normal months have been a bit less than cold months but certainly not as rare as cold months were during the 2000s.

The 2000s had a total of 30/120 colder than normal months, in regards to the Irish Mean Temperature (IMT).

The 2010s so far has had a total of 38/87 colder than normal months so there's already been more cold months in the 2010s than the 2000s. This is to compensate for how warm the 2000s were in Ireland. The only year with 1 colder than normal month during the 2010s so far was 2014 which is the UK's warmest year on record. Ireland's warmest year on record is 2006. The 2000s also did not have any really record breaking cold months unlike the 2010s. The 2010s has had December 2010 and March 2013. Due to compensation, I think we can expect a very cold month sometime near in the future.

I tend to focus on the Pressure and Mean Temperatures when doing ENSO and Irish weather correlation. Pressure so I know we'll have the right setup for a favourable weather pattern and the mean temperatures for basically the same thing. ENSO has tended to have more effects on the Winter than any other season in this part of the world. I agree with the theory because the winters are the season that tend to have some similarities during ENSO events unlike other seasons which tend to differ significantly so. I wouldn't rely on ENSO (well I wouldn't rely on it for anything in Ireland.... always consider other factors for making forecasts on Ireland's weather) for other seasons.

Remember that no El Nino or La Nina event is the same regardless of the strength but there are some interesting theories that have come off of them which I won't argue with like how a very strong El Nino will make one of the Winter months record breakingly warm. During the only three very strong El Ninos in history, there has been a succession of record breakingly warm Winter months. The very strong El Nino winters so far have been 1982/83, 1997/98 and 2015/16. 1982/83 had a significantly mild January (one of the mildest on record but not THE mildest on record), 1997/98 had the warmest February on record and 2015/16 had the warmest December on record.