Okay, I took a look at all cases of late April temperature drops relative to first fourteen days (only the warmest 8% of early Aprils were in first sample, granted they would stand a better than average chance of seeing a drop of 1.0+, just about the entire 50% below average first fourteen days would likely be excluded by seasonal trend alone) ...
... that leads to following table of all cases with drops of 1.5 C or more (a total of 51 out of 252 dropped by at least 0.1 C and 11 stayed level). ...
YEAR ___ CET 1-14 _ CET 1-30 _ decrease
1778 ___ 10.7 ___ ____ 8.2 ___ ___ 2.5
1815 ____ 9.9 ___ ____ 8.1 ___ ___ 1.8
1884 ____ 8.9 ___ ____ 7.2 ___ ___ 1.7
1859 ____ 9.1 ___ ____ 7.5 ___ ___ 1.6
1906 ____ 8.9 ___ ____ 7.3 ___ ___ 1.6
1835 ___ 10.1 ___ ____ 8.6 ___ ___ 1.5
1981 ____ 9.3 ___ ____ 7.8 ___ ___ 1.5
This list adds only four cases (1884, 1859, 1906, 1981) to identify all drops of 1.5+, now working on a program that can isolate cases where second half of April was colder than Feb - march. I wouldn't be surprised to find one or two.