Is it possible to add a chance to this?

I made a thunder enchantment, it can be applied to axes and swords. i need it to spawn thunder at a 20% chance. is it possbile?
{
    "description": "Thunder",
    "supported_items": [
      "minecraft:diamond_sword",
      "minecraft:golden_sword",
      "minecraft:iron_sword",
      "minecraft:iron_sword",
      "minecraft:netherite_sword",
      "minecraft:stone_sword",
      "minecraft:wooden_sword",
      "minecraft:diamond_axe",
      "minecraft:golden_axe",
      "minecraft:iron_axe",
      "minecraft:netherite_axe",
      "minecraft:stone_axe",
      "minecraft:wooden_axe"
    ],
    "primary_items": "#minecraft:swords",
    "weight": 1,
    "max_level": 1,
    "min_cost": {
      "base": 20,
      "per_level_above_first": 5
    },
    "max_cost": {
      "base": 30,
      "per_level_above_first": 5
    },
    "anvil_cost": 25,
    "slots": [
      "any"
    ],
    "effects": {
      "minecraft:post_attack": [
        {
          "enchanted": "attacker",
          "affected": "victim",
          "effect": {
            "type": "minecraft:summon_entity",
            "entity": "minecraft:lightning_bolt",
            "join_team": false
          }
        }
      ]
    }
  }

what i have till now