The climate is influenced a lot by the North Sea, which is deep
enough to act as a heat sink and smooth out extreme temperatures,
while being shallow enough to allow for a few weeks of quite hot
weather (30+ degrees Celsius) in the summer and a few weeks of cold
(under -5 degrees Celsius) in winter.
Winds from the north and west approach the Netherlands across
the North Sea, leading to cooler springs and summers, and milder
autumns and winters, all with lots of rain or snow. When the winds
turn and blow from the south and east this results in mostly dry
weather, with warmer temperatures in spring and summer, and colder
autumn and winter.
Since the Gulf Stream is aimed directly at the North Sea the
climate is a lot warmer than most other areas at our latitude. In
January 2012 for example Great Britain and the Netherlands were the
last areas north of the 50N latitude to receive any significant
amount of snow.
Related Q&A:
What is the climate of the Benelux countries?-Well, the Benelux countries, which include Belgium, the Netherlands, and Luxembourg, have a temperate maritime climate. You know, that means they have mild winters and cool summers. There's quite a bit of rainfall throughout the year. Oh, and the weather can be quite changeable. One day it might be sunny and warm, and the next it could be cloudy and rainy. But overall, it's a climate that's relatively pleasant and suitable for various activities and agriculture.