Brussels weather forecast
For a country that gets 852mm of rain per year (less than the Netherlands, more than the United Kingdom) it pays to know if there will be a thunder storm or just light rain where you are and where you're going.
It is a fact that it rains a lot in Brussels, but not monsoon-style rain, it is typically a light 'spit' most afternoons and evenings. A good fold-up umbrella in your travel bag during spring and autumn is enough to protect you. In winter, a waterproof jacket and boots are handy as the wind does get a bit strong.
Best sites for Brussels weather forecast
Royal Meteorological Institute of Belgium
The authority on Belgian weather is the Royal Meteorological Institute of Belgium (RMI). This institute issues the official weather forecasts for Belgium. It has research stations in Uccle and Dourbes. No matter where you look at weather forecast - Google, Le Soir, De Standaard or online weather sites, it will be probably sourced from RMI. Their website is easy to use, available in Dutch, French, German and English.
Le Soir and De Morgen have comprehensive weather guides on their online newspapers. In French weather is called "meteo". On the Le Soir website, it's under the Services section. In Dutch, weather is "weer". Find these words in the daily newspapers. Or their online versions.
Alternatively, you can always go to Google and type "Brussels weather" into the search bar. This will bring up the weather forecast as the first result. You can simply take note of the current temperature, current status and forecast for 4 days.