Despite bastardization in recent years to the alternate (Read: "Gay") spelling, [Narley], gnarley is akin to [rad] - a late-1980s - early-1990s term, meaning "exceptional", or "[cool]". Developed on the West Coast, and used primarily by sufers and skateboarders.
> "Hey bra, d'dya scope that gnarley tide?"
> "Tscha! That was a ripple, man!"