Diablo III- Skills Article CXXXXIII: The Wizard, Force Skills- Blizzard

Blizzard (45 Arcane Power): The target area (with a roughly 8 yard radius) suffers a hail of ice for the next 6 seconds, dealing 35% weapon damage as Cold damage per second to all enemies within that area.  This damage does not stack with itself.

Ah, Blizzard.  Your tradition of putting your namesake spell into every game you make which has magic in it is reliable- and fun, because who doesn’t like calling down a storm of frosty death, even just now and then.  Blizzard is a bit quirky in a way- while you can have as many active at once as you can afford, it is one of the few damage over time area effects that flat out doesn’t do anything extra when you overlap it with itself- only one Blizzard can damage each enemy at a time.  On the other hand, the area it affects, while large enough to be tactically useful, is small enough that sometimes you wouldn’t want to overlap them anyway- so it’s at most a minor drawback.  By combining decent damage over time with the natural slowing effect of cold damage, Blizzard sets itself up as a highly useful tactical skill, pinning things down and damaging them.

Grasping Chill (45 Arcane Power): The target area (with a roughly 8 yard radius) suffers a hail of ice for the next 6 seconds, dealing 35% weapon damage as Cold damage per second to all enemies within that area.  This damage does not stack with itself.  When this effect ends, the area is filled with a cold mist that lasts 3 seconds and Slows enemy movement by 60% for 3 seconds.

If you use Blizzard purely for the tactical purpose of slowing enemies, and don’t care so much about the damage, this rune is very useful, setting up a highly persistent slowing area that will let you keep control of the flow of battle far longer than the base form of the skill.  Very useful for kiting, if you have the right skills to do so.

Frozen Solid (45 Arcane Power): The target area (with a roughly 8 yard radius) suffers a hail of ice for the next 6 seconds, dealing 35% weapon damage as Cold damage per second to all enemies within that area.  This damage does not stack with itself.  Each second during which a creature is damaged by Blizzard, it has a 20% chance of freezing that enemy solid for 3 seconds.

Frozen Solid enhances Blizzard’s ability to pin enemies into one location.  Where Grasping Chill is best used as a kiting tool, keeping up a slowing area for you to draw enemies into and across, Frozen Solid is for pinning a group in place and reducing its damage output.  This makes it slightly more defensive, and much more useful to players who hold still to deal out their damage.

Snowbound (20 Arcane Power): The target area (with a roughly 8 yard radius) suffers a hail of ice for the next 6 seconds, dealing 35% weapon damage as Cold damage per second to all enemies within that area.  This damage does not stack with itself.

The Snowbound rune for Blizzard is used to affect multiple separate groups- cutting the Arcane Power cost of Blizzard by more than half gives you the opportunity to lay out more Snowbound zones than you could ever manage Blizzard zones, and thereby cripple enemies in completely different parts of the battlefield.  Alternately, this works well with builds whose other skills are high in Arcane Power cost by reducing the amount spent on your battlefield control so you can reserve your resources for damage dealing.

Stark Winter (45 Arcane Power): The target area with a 22 yard radius suffers a hail of ice for the next 6 seconds, dealing 35% weapon damage as Cold damage per second to all enemies within that area.  This damage does not stack with itself.

If you’re more worried about large groups, or how quickly enemies manage to escape or traverse the area that Blizzard effects, then Stark Winter more than triples the total area affected by Blizzard, making it virtually impossible for an enemy to cross the whole thing before the skill itself wears off.  Act 3 is where this is most useful, as the battlefields and Crater tend to have many large or spread-out groups of enemies.  It’s not as nice in Act 2 or Act 4, but both of those acts still have some situations (especially in their dungeons) where the increased area is fairly strong.

Unrelenting Storm (45 Arcane Power): The target area (with a roughly 8 yard radius) suffers a hail of ice for the next 8 seconds, dealing 35% weapon damage as Cold damage per second to all enemies within that area.  This damage does not stack with itself.

When you already have ways to keep enemies corralled and your allies need them to hold still enough to get their faces beaten in in melee combat, then you want Unrelenting Storm.  By extending the duration and keeping the same rate of damage, not only does Unrelenting Storm deal more total damage, but it also keeps things slowed down for longer.  If nothing really crosses your Blizzard area too quickly, but you want more opportunities to either lure things into it or have your friends beat on things that are slowed, then this is a good choice of rune.