The article that started it all, "The Power of Sorcery" from
Pyramid #3/63, established a trend of converting explosive spells to simpler (if arguably less realistic) area effect spells. Under that approach, it becomes somewhat confusing what an "improved" area spell should be, but for
GURPS Sorcery: Sound Spells gave a simple answer for Improved Concussion: double the radius. I followed that precedent for Improved Explosive Lightning.
Improved Concussion
This spell has a canonical writeup in GURPS Sorcery: Sound Spells, p. 7.
Improved Explosive Lightning
Keywords: Area (Fixed), Missile, Obvious.
Full Cost: 19 points/level.
Casting Roll: None. Use Innate Attack (Beam) to hit.
Range: 100 yards.
Duration: Instantaneous.
Creates a lightning bolt that inflicts 1d burning surge damage on all targets within 8 yards of wherever the attack lands. The attack roll gets a +4 bonus for targeting an area.
Metallic armor counts as DR 1 against this attack, but nonmetallic armor protects normally. Targets stuck by this attack must make an HT roll, at -1 per 2 points of penetrating damage, or be physically stunned. On subsequent turns, they can roll HT to recover. Lightning behaves unpredictably around conductors; see Lightning (GURPS Magic, p. 196) for more details.
This is also a Weather spell.
Statistics: Burning Attack 1d (Area Effect, 8 yards, +150%; Nuisance Effect, Behaves erratically around conductors, -5%; Sorcery, -15%; Surge, Arcing, +100%; Side Effect, Stunning, +50%) [19/level]. Notes: This spell originally appeared in GURPS Magic: Artillery Spells, p. 29.