Most travelers to Siem Reap visit during the cool, dry high season, from late November through end of February, when it gets incredibly crowded, and after that, during the hot dry months of March and April. I like to encourage people to visit during our 'green season' or wet season and the monsoon months of May to November. The rain is unpredictable. It doesn't rain like clockwork in the late afternoons. But this is what the Tropics are meant to be like and it's incredibly gorgeous and green.