天気

1. Origins, structure, and basic meaning

• Structure: 天気 (てんき) is a noun for weather, the condition of the atmosphere.
• Basic usage: It appears in a plan conditional on good weather or a description of rapidly changing mountain weather.
  • 天気がよければ公園で昼食を食べます。 — If the weather is good, we will eat lunch in the park.
  • 山の天気は変わりやすいので、空をよく見ていました。 — Mountain weather changes quickly, so we watched the sky carefully.

2. Common pitfalls and similar expressions

• Weather state and condition
  • 天気がよい describes good weather, while 天気がよければ makes that state a condition for another action.