The party can seek shelter near a trio of shielding stones, magical rocks that project an aura of lightning resistance. Just be careful, if they absorb too much lightning they'll detonate in a thunderous boom. Adventurers should also try to avoid getting grappled by a thunderquill, they've been know to skewer adventurers on their quills, hoisting them high overhead and making them a tempting target for lightning strikes.
DM and player versions of the map are attached, though there's not much difference, and the encounter is there as well. Enjoy!