I have already written an article about the use of “would” after “wish” when we speak about states and present or habitual actions. As was pointed out by one of my readers, the article didn’t consider the case when the wish is about something that may happen in the future or might have happened in the past.
The general rule for the verb to wish is that it is followed by the past subjunctive of whatever verb you would use when not speaking about a wish. For example:
since the past subjunctive of “be” is “were”. Similarly:
There is no “pluperfect subjunctive” mood in English (past subjunctive of verbs that are already in the past), so we use the past perfect instead (just like in reported speech), i.e. it has the same form as above:
However, what if the action is to take place in the future? We would use “will” for the future tense, and the past subjunctive of “will” is “would”, so, in accordance with the general rule, we say:
It will not rain tomorrow. → I wish it would rain tomorrow.
You will not go to the party. → I wish you would go to the party.
This last usage distinguishes wishes from conditional sentences. We would say, for example, “if it rains tomorrow …” to express a real condition in the future and “if it rained tomorrow …” to express an unreal condition (i.e. something that is unlikely to happen), but we would never say “if it will/would rain tomorrow …”.