What does "formal attire" mean?

In general, this is an evening wedding, which according to the books is the most formal time of day. The wedding will be outdoors, so you should dress for evening weather. But remember that it will be summer and the days are long up here in the great north, so it probably won't get that chilly.

For the fellas, "formal attire" means something more than casual and less than black tie. There will be NO TUXEDOS at the wedding (not even me, the groom, or my swarthy crew of groomsmen.) Seattle is a casual place, but do yourself a favor and leave the fleece and denim at home for just this once. You should wear whatever makes you feel fancy and happy, so you can maximize on the fun.

For the ladies, you are welcome to wear a dress or whatever makes you feel fancy and happy. Both cocktail dresses and church clothes are fine. The wedding is in a garden. We'll be walking on grass so plan your heels accordingly. For reference, the bridesmaids will wear knee length black dresses.