From Minecraft Wiki:
Electrified Creepers
Charged Creepers (aka Electrified Creepers) are the latest of monsters that players need to be on the lookout for should a lightning storm brew. If during a storm lightning strikes a Creeper, it will become electrified. This is an extremely rare occurrence. The explosion from an electrified creeper does increased damage and has increased range. They are easy to differentiate from normal creepers by the blue glow surrounding them.
Electrified creepers can cause huge amounts of damage. The player's shelter is only truly safe from them when using Obsidian as a construction material. Due to the increased blast radius, it is extremely hard to cancel a charged explosion, as they will continue to swell up.
I am starting to feel that weather is good, but I am going to turn it off (I have Single Player Commands so I can turn it off) when I see a creeper chasing me and lighting hits nearby (not on the creeper though) I will turn it off. Or I can use fly to get out of the blast radius, which I don't want to know the size of.