In article ,
Evert Wesker writes:
The January data from Holland. Up to 1899 it is the so called
"Labrijn reeks", after that the data from De Bilt. The range is not
homogeneous. However, it gives you a nice idea.

Very interesting. Severe months seem to be much colder in Holland than
in the UK. It's surprising how much difference 100 or so kilometres of
sea can make.

Which is the earliest year for which you've included data?
--
John Hall
"Honest criticism is hard to take,
particularly from a relative, a friend,
an acquaintance, or a stranger." Franklin P Jones