The weather in the Netherlands is very unpredictable. You could be having a sunny day and then suddenly the rain will start pouring. That is why most Dutch citizens keep an eye on the daily weather reports on TV or have weather forecast apps on their phones. The Netherlands may be a small country, but it has different types of weather in each different province. For example, it could a very bright sunny day on a coastal city while it is very windy and rainy in a neighboring province.
Spring and summer
The spring weather starts around march in most of the country. Temperatures start to warm up and outdoor activities start to be more and more common. People start to really enjoy spring around April where the country sees more and more sunny days.
The summer starts around the end of June. School holidays start around that time which means families get to go on holidays and you notice more kids playing outside due to the pleasant weather. The heat however some people might find unbearable and either stay inside during high noon or go swimming in one of the lakes or beaches.
Autumn and winter
Autumn weather begins around the end of September. The wind starts to pick up and you will see the occasional rainy days. The weather around that time of the year starts to cool down and outdoor activities start to diminish. Some cities like Rotterdam experience frequent windy days which makes it unpleasant to some people. Winter weather start around end of November. By then temperatures start dropping to their lowest but usually not freezing. In the recent years temperatures have dropped below zero but just a few times.
Each season in the Netherlands has its own charm, so you should try to enjoy each one and be ready for weather changes. You can also try downloading on of the many weather forecast apps, that can give you a better idea of how warmly you should dress during the time you want to go outdoors.