I go by several things when deciding when to plant my tomatoes. What the average lows for the time are, what the long term weather trend is, and how big my tomatos are.

With the next week looking good and it heading into the second half of May, when traditionally the weather is warm enough, I decided it was time and planted them on Friday.

It is always possible for the weather to take an unexpected turn for the worse, so I am prepared with enough large pots and buckets to put over the plants should the temps dip too low. I think in the 15 years I have been growing tomatoes, I have had to do that only once or twice.

BP

Bonnie makes a good point. Lots of issues at play. In your case, I think you can certainly plant them out.
Flexibility is an important asset in planting out. Just as some springs are cold, with late frosts, there are also warm springs where the last frost occurs earlier than usual. The last frost date simply represents a 50% average. One thing you should not do is go by the calendar alone. Instead, consider temperature trends, forecasts and soil temperatures.

I planted most of my tomatoes and peppers. Still waiting on eggplants,squash and okra. Do I think I've dodged frost for the season? No, but I'm prepared to use row covers if needed. Do I think I've dodged hard frosts? Yes. I still have some backups though.

Nothing is guaranteed in gardening. An August frost can wipe out all warm season crops. So take advantage of any 'season extensions' you get, even in spring.

Well we planted out some tomatoes yeaterday. Just a start,
Today as much as I can goes outside.And I will be planting into the garden all week. It is going to be a busy time. Plus I am giving some away to people I promised. and still selling some.

Victoria Day weekend is traditionally the time we plant our tomatoes in the Montreal area (Zone 5a). However, I would have planted this past weekend because the weather is exceptionally nice, but I ran out of time.