grammar - "Wasn't" vs "weren't"

Which one would be correct?

1. I wish it weren't raining today.


2. I wish it wasn't raining today.


3. I wish it were raining today.


4. I wish it was raining today.

Answer

The fact that you wish something was or wasn't true means you should use the indicative. You are stating that something is factually one way or another, and wishing for the situation to be reversed. So "I wish it wasn't raining today" and "I wish it was raining today" are how to express those concepts.

If you were trying to imply something contrary to fact, then were would be the way to go.

If I were you, I wouldn't be wishing it wasn't raining: rain is good for your garden.

Edit: Because Stan Rogers, whose opinion I respect, has weighed in with the polar opposite viewpoint from mine, I feel obliged to elaborate.

Morton S. Freeman, writing in A Treasury for Word Lovers, elaborates on a parallel idea using if clauses:

Some people have a mistaken belief that a clause beginning with if must always be in the subjunctive mood, reflecting doubtful fulfillment of the condition or a condition contrary to fact. This is not so. A clause introduced by if may express a simple condition relating to the past and take the indicative form of the verb. For example, in "If Allan was there, he was drunk," the if clause introduces a supposition, hence a verb in the indicative mood. And so with the sentences "If Curran was absent, he was probably out of town" and "If I was long-winded, I'm sorry." None of the examples imply doubt or suggest circumstance contrary to fact, as in "If I were President, I wouldn't pardon him." [Emphasis added.]

I think you can see the parallel here. Far from indicating a circumstance contrary to fact, the "I wish" construction is lamenting an actual fact. So subjunctive mood is not called for.