Have they set any fruit at all? Once they hit 5-6 feet, mine tend to slow down a bit and focus more on ripening their fruit.

If they've not set fruit, any leaf curling, blossom dropping, or diseases that are noticeable?

Lastly, how much sun (and what quality) do they get. (i.e. 10 hours, 80% direct sun)?

Answering a few of those might spark some additional answers. Doubt the cold winter has anything to do with it though.

What varieties are you growing ?
What kind of temperature, direct sun you are getting.

I agree, you cannot blame winter in the middle of summer.

Finally if you can post a picture might help you to get better help.

The variety you're growing can make a huge difference. Determinate tomatoes only grow for a certain amount of time and then stop.

You might want to stick to indeterminate hybrid tomatoes. Early girl tomatoes are good options for those who live in areas with short growing seasons. You might want to check with staff at nurseries next season about what they recommend for your area.

For example, I've made the mistake of growing heirlooms in the past because the pictures are "different" and "cool looking." What I didn't realize is that they're much more fussy than your traditional hybrids.