thunder
霅 centers on thunder, the loud sound accompanying lightning during a storm.
霅 combines 雨 (rain) with 言 (words/sound), likely representing the sound of thunder during rain. The exact historical development is uncertain.
Rain 雨 falls from the sky, and the sound 言 below represents the loud words of the storm: thunder.
For ショウ, imagine a dramatic thunderclap that makes everyone say 'Show!' as if the storm is putting on a performance: Show -> ショウ.