'It often doesn’t rain in summer' OR 'It doesn’t often rain in summer'
how and why

Question

Answer

The first means: frequently, an entire summer has very little rain.

The second means: during the summer season, it seldom rains.

Answer

In your example, they are both possible, although the first to me suggests that you are talking about a series of summers, in which several have no rain at all, and the second is talking about a single typical summer, which would be mostly dry.