I am in Portland as well and enjoying the beautiful weather
Things that would go well with the weather are:
Mineral water with a sprig of mint in it, or a lemon wedge, or a lime wedge or both or just plain
Juice with a splash of 7-up
Ginger Ale
and many other things...
No reason to put any type of alcohol in them. Just my opinion though. I am also having dinner outside but never even thought about alcohol with it.
Found this site that you might find useful it has several good ideas:
http://glutenfreecooking.about.com/o...mmerdrinks.htm also this one looks good:
http://www.drinksmixer.com/cat/8/