Counterspell & Dispel Magic vs Wild Magic Surge

Question

One of my 5th ed games has both a wizard and a Wild Magic Sorceror in the party. It's unlikely to come up in play, but I was wondering if:

a) the wizard could cast 'Counterspell' to stop a Wild Magic Surge

b) the wizard could cast 'Dispel Magic' to cease any ongoing effects from the surge

My gut feeling is that a) is unlikely, since the surge is not a spell per se and that b) might work, but only for the ones that are specifically labelled as spells and have an ongoing effect, but I'd appreciate the help of someone more experienced than me.

Answer 1

Only wild magic effects that specifically cast spells can be managed with these methods.

Looking at the Wild Magic Surge table (PHB, p. 104), there are generally four categories of effects that can be rolled:

1. Effects that cause you to cast a spell. Examples include fireball, confusion, fog cloud, fly, etc. Since you are casting a spell, these can be counterspelled by you or another spellcaster. When these spells have a duration (such as fog cloud, or mirror image), they can also be ended with dispel magic.
2. Effects that cause an ongoing non-spell effect. Examples include changing your height, growing you an extra eye, you (or other creatures) becoming invisible, etc. Since this is not a spell, it can't be ended by dispel magic. Some effects indicate how they can be removed (for example, the skin color change on a 23-24 roll), but beyond that, the wild magic surge effect can't be ended.
3. Effects that cause an instantaneous non-spell effect. Examples include dealing lightning damage to all creatures near you, teleporting you, or restoring all of your sorcery points. Since these aren't spells or an ongoing effects, they can't be counterspelled or ended with dispel magic.
4. Non-spell effects that summon a creature. Examples include a modron, flumphs, or a unicorn. Summoned creatures generally can't be dismissed with dispel magic.

So why can't dispel magic help, especially for cases like category #2? Here's the spell wording:

Choose one creature, object, or magical effect within range. Any spell of 3rd level or lower on the target ends.

And here's a very important clarification from the Sage Advice column:

Dispel magic has a particular purpose: to break other spells. It has no effect on a vampire’s Charm ability or any other magical effect that isn’t a spell.

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By my count, of the 50 different effects on the Wild Magic Surge table, nine of them can be counterspelled, and seven of those (all except fireball and magic missile) have durations and can be dispelled.

Answer 2

Both options a) and b) should work for Wild Magic surge effects that involve casting a spell. These effects use wording like this:

You cast fireball as a 3rd-level spell centered on yourself.

And Counterspell lets you

[...] attempt to interrupt a creature in the process of casting a spell.

So, since the sorcerer casts the spell when a Wild Magic Surge calls for it, you should be able to use Counterspell to prevent it from happening.

By the same token, Dispel Magic lets you:

Choose one creature, object, or magical effect within range. Any spell of 3rd level or lower on the target ends.

So any effect of a Wild Magic Surge that involves a spell with a non-instantaneous duration should be able to be dispelled.