If you surf to http://www.knmi.nl/waarschuwingen_en_verwachtingen/ you'll see the 'Langjarige gemiddelden, tijdvak 1971-2000' or 'Long Term averages during 1971-2000' at the bottom of the page. Nice to make some graphics in December (the darkest hour is just before dawn). However you'll have to visit the site every month for a year if you want more. Thanks to the internet archive at http://www.archive.org/ this task is less daunting.
The ODF-sheet: long_term_temperatures_the_netherlands.ods License Creative Commons By-ShareAlike
The graphics:
