ToME: the Tales of Maj'Eyal

Rhaloren camp, inexisting Elven Tempest hitting the character from the X spot below.

Nothing much in the stdout:
[SPELL CRIT %] 2
[PROJECTOR] starting dam 5.3333333333333
[PROJECTOR] after difficulty dam 5.3333333333333
[PROJECTOR] res 1.8571428571429 0.98142857142857 on dam 5.3333333333333
[PROJECTOR] after resists dam 5.2342857142857
[PROJECTOR] final dam 5.2342857142857
[LOG] Elven tempest hits Senyakaze for #ROYAL_BLUE#6 lightning#LAST# damage.

I vaguely remember seeing something like this once. I believe it is the Thunderstorm effect not properly disappearing when the tempest dies.

Yup this is probably it. And the effect won't go away, even when leaving the level or quitting/reloading the game. So the thunderstorm effect is bound to the location forever.