Willow’s Bounded Tempest

A mighty tempest grows inside of you. For the duration, your walking speed increases by 5 and you gain a +1 bonus on strength checks. 

As an action before the spell ends you can end the spell to let the tempest out. All creatures in a 20 foot sphere centered on you must make a strength saving throw, taking 1d8 bludgeoning damage on a failed save, or half as much on a successful one. Additionally, creatures who fail the save are knocked prone and are flung 10 feet in a random direction. If the flung creature hits another creature, the other creature is also knocked prone.