thunder on a clear day; thunder from a blue sky
Refers to thunder occurring when the sky is otherwise clear, often considered an unusual or ominous phenomenon. Typically written as 日雷.
Today, even though it's sunny, there was thunder from a clear sky.
lightning that starts a fire; fire-causing lightning
Lightning strike that ignites a fire. Often written as 火雷 or 火神鳴り. Related to 水雷 (みずがみなり, lightning accompanied by heavy rain).
See also: 水雷 (みずがみなり)
Fire-causing lightning struck and started a forest fire.
水雷 refers to lightning accompanied by heavy rain, while 火雷 (sense 2) is lightning that causes fire.
Primary spelling for 'thunder on a clear day' (sense 1).
Spelling for 'lightning that starts a fire' (sense 2).
Alternate spelling for sense 2, using 神 (god) and 鳴り (rumbling).
Irregular okurigana usage; rare variant of 火神鳴り.
Compound of 日 (sun, day) or 火 (fire) + 雷 (thunder). The reading ひがみなり is a combination of ひ (hi, sun/fire) and かみなり (kaminari, thunder), with rendaku voicing. The exact historical derivation is uncertain.