Looking ahead to June the pattern matching suggests a fairly good chance of a warmish month.
If we look at years since 1950 with an April CET of around 9-9.5C and a May CET between 10.7C and 11.5C we have the following matches with their June CET figures and July/Aug CET means
Year June CET Jul/Aug CET
1957 15.2C 15.9C
1963 14.9C 14.8C
1980 13.8C 15.3C
1993 15.0C 14.9C
1995 14.3C 18.9C
1997 14.1C 17.8C
2005 15.5C 16.6C
2010 15.2C 16.2C
71-00 14.1C 16.3C
So maybe a fairly warm June but July and August could be disappointing on these figures. 1995 and 1997 stand out as being a bit different. In these years the June CET was only average but July and August were very warm. So maybe we should be hoping for an average rather than a warm June.
The only year in the above list that was in a similar phase of the ONI index (i.e. moving towards a moderate El Nino event) was 1993. In 1993 we were also in a very similar phase of the solar cycle as we are now - i.e. heading down towards a solar minimum.
So I think it is worth keeping an eye in the coming months on whether this year shapes up in a similar way to 1993. The second half of 1993 was particularly cold with a mean CET of just 10.1C (compared to the 1971-2000 figure of 11.5C). We had 5 consecutive months from July to November where the CET was more than 0.5C below the 1971-2000 mean. So after the record breaking warmth of 2014 maybe 2015 will revert to being a rather chilly year. If the rest of 2015 saw temperatures similar to 1993 the CET for 2015 would come in at just 9.2C.