Lord Cirrus in Gianthold

[Bonulino]

How do I kill him? He keeps hitting me with nearly continuous sleet storms, so I can't see him and I can't get close enough to him to strike him. Plus, he self heals pretty fast.

[Hobgoblin]

ranged weapons, casters work well, failing that get fom either from spell or items

hob

[Lithic]

get freedom of movement from either a spell or item, or get one of the 2 or 3 named boots that prevent slipping on slippery surfaces (spiked boots and i forget the other).

That will stop your slipping around. You can also get a hireling to help you (either a cleric to heal you, or a sorc to blast him).

If you use maladroit weapons, you will drop his dex to 0 pretty fast and stop him from casting spells.

Also if you can use UMD, but arren't a spell caster, spam him with enervation scrolls.

[Isolani]

Kill him and the sleet storm goes away.

[vVAnjilaVv]

He can see pretty far as well and he has See Invisibilty...so you can run up until you get his aggro and just kite the Storm and Fire Giants down the ramp that are usually up there.

The minotaurs, trolls, and Ogres won't see you...just don't run too far or they will rubberband and also don't swing until you are out of sight of the rest of the mobs.
If you are trying to do this with that Barb in your sig get a good vertigo weapon and trip him.....those big giants are really easy to trip.