also: ぴいかん
noun
clear weather; fine weather; perfect weather
Colloquial term for cloudless, sunny weather; originally filmmaking jargon for ideal outdoor shooting conditions. Often used in casual conversation.
明日はピーカンらしいから、海に行こう。
Tomorrow is supposed to be perfectly clear, so let's go to the beach.
今日はピーカンで、雲ひとつない。
Today is a cloudless, perfect-weather day.
Originally filmmaking jargon, possibly from a contraction or onomatopoeic expression for bright, clear conditions; the exact derivation is uncertain.