There may be a difference in certain regions, but usually swarms are a spring thing, with another small reoccurrence in autumn. Mid summer is quiet and winter has none.
This relates to the times at which a queen can mate - there are no male drones in winter (the females kicked them out!) and so any queen that hatched would be a virgin, and couldn’t lay.
Sometimes swarms will occur due to bees absconding to get away from High levels of disease. I have never seen this but high levels of varroa can cause it.