falling rain or snow
霏 centers on precipitation in the form of falling rain or snow, emphasizing the visual of something descending from the sky.
霏 combines 雨 (rain) with 非, which likely contributes the sound and the idea of something spreading or falling in a scattered way, suggesting rain or snow falling thickly.
Rain 雨 falls in a scattered, non-uniform way (非 suggests negation or scattering), creating a scene of falling rain or snow.
For ヒ, imagine the rain falling so thickly it makes a hissing sound: 'Hee!' — the hiss of heavy rain cues ヒ.