Sigil of tempest is a technique in SLASH'EM. When used, it creates 3x3 explosions around you centered in a 7x7 area (excluding the 3x3 area around you, so you will not be hit) instead of firing a ray. This technique affects all ray-based spells except finger of death.
When used with sigil of control, the explosion can be controlled as if you cast fireball or cone of cold at skilled level or above in vanilla NetHack.
When used with sigil of discharge, the number of explosions doubles.
Most ray-based spells in SLASH'EM, as well as fireball
explosion, use six-sided damage dice. It seems sigil of tempest explosions were supposed to deal (XL/4 + bonus)d6 damage
, however, due to what is probably a bug, they do only plain (XL/4 + bonus) damage
, resulting in single digit damage in most cases, making the technique mostly useless.