Whenever there is a weak nectar flow or on and off nectar flow, swarming can be an issue.
Unreliable nectar intake this time of year, makes the bees nervous that not enough food is coming in and they may have to leave to find a more steady food supply.
Stay on the looking for swarm cells program during this time.
If the weather warms up and the nectar flow gets more steady, the swarming issue will lessen.