The spell creates a zone of cold. Spell is concentrating.

When cast, a creature within a 20ft diameter circle in 30ft of the caster centered on a point the caster can see is dealt 2d6 force damage.

Any creature in the circle must roll a Con Save against your spell DC. On a success, creatures take half damage.On a fail, the creature is stunned until the end of their next turn. If you end your turn in the circle, you must roll a con save. You can Reroll the save at the end of your turn. 

At the start of each turn after the spell has been cast the following chart is to referenced.

1st turn: take 2d6 Force damage and roll con save. On Success take half damage or take full damage and be stunned.

Turn 2: Take 1d6 cold damage and roll Con save. On Success take half damage or take full damage and be stunned.

Turn 3: Roll d100, on 80 or above Con drops by 1, roll Con save. On Success take half damage or take full damage and be stunned.

Turn 4: take 1d6 cold damage and roll d100, above 80, Con drops by 1 (does not stack with previous turn), roll con save. On Success take half damage or take full damage and be stunned.

Turn 5 through 10: take 1d6 (goes up by turn count to max 6d6 by end of turn 10), roll d100, anything above 60 roll d4 and subtract from Con (starts to stack with previous rolls, if Con becomes 1 target is frozen), roll con save. On Success take half damage or take full damage and be stunned.

If creature is frozen, Greater Restoration can be used to counter frozen condition. 

When cast at at a level higher than 4, add 1d6 of force damage for every two levels upcast.