Family friend once claimed there was a fruiting specimen being grown outdoors in the mild Ballard neighborhood of Seattle when he was a kid. But I have never seen one this far north myself. And there are quite a few Zonal Denial gardens and gardeners around these days. If anybody here has one it is in a sheltered nook in an unusually soft spot near salt water.

And it isn't likely to be very old.

Sunset Western Garden Book says Guatemalan varieties are usually good to about 30F/-1C, with hardier Mexican ones taking 24F/-4C or lower. If you drop down another whole 10F that's still only 14F. None of the Sunset climate zones it gives for growing avocado trees are found north of California:

Avocados bloom in late winter to late spring, so even though older trees will survive these lows, temperatures much below freezing will damage flowers or fruit

Since I have 2 or 3 of them, I think I'll pot one for indoors and see what the outside ones do. You never know!