The enjoyment of a visit to any largely outdoor attraction depends a lot on the weather! LEGOLAND Windsor is not the best place to visit in the rain: having said that, an overcast day with the odd shower drives away large crowds, whilst being perfectly manageable (the likes of Laser Raiders and the Imagination Theatre are great indoor attractions).
I've personally always found BBC weather forecasts to be most accurate, so below you will find their three day forecast for Windsor: