I've had tomato plants blight off in August. You definitely don't want damp and chilly conditions to occur around the vines. If the fruits are too green to pick you will have to erect plastic shelters over the plants so they can hang on longer than if they were fully exposed. This must be done before the plants start to shrivel and get moldy.

In this region it is not unreasonable to grow tomatoes under cover the whole summer. Especially if you are trying to get fruit from kinds that are not short season types.

Green tomatoes are far less likely to rain-crack, but you should bring yours inside to ripen.

Temperatures under 45 degrees ruin tomato quality for fresh eating.