noun
A somewhat formal or literary term for pleasant, clear weather. In everyday conversation, いい天気 or 晴天 are more common.
好晴の空の下、運動会が行われた。
The sports day was held under a clear sky.
明日は好晴に恵まれそうだ。
It looks like we'll be blessed with fine weather tomorrow.
Compound of 好 (good) and 晴 (clear weather). The reading こうせい is the on'yomi for both characters.