Thanks for that DOCARCH, looking back at previous contest results, only one May has had a MIN comparable to this year, namely 2012.
These are the MINs going back from 2018 to 2011:
-1.2, -1.5, -1.4, -0.8, +1.7, -0.5, -3.6, +2.1.
I was going to go a bit further but the archives get all scrambled up at some point.
That -3.6 in 2012 was on the 6th at Casement.
This year we reached -3.1 on 5th at Mountdillon. Hourly of -2 at Markree on 6th may indicate another one to watch perhaps.