Whenever you have:
- an affix verb form,
- with a vav-conjunction, and
- it is the first word of the clause;
then this verb is reversed in much the same way as a vav-conversive “converts” a prefix form. It reverses the affix form of the verb from past tense, to future tense. Hence, KHW (8.1d) refer to these as “vav-reversives”. On occasion, a vav-reversive converts an affix More detail on the syntax of these forms is here.