thunderclouds

noun
  1. 1

    A large, dark cloud, usually a cumulonimbus, charged with electricity and producing thunder and lightning; a stormcloud

  2. 2

    (by extension) Something menacing and brooding.

    โ€œthe ominous thunderclouds of warโ€

Source: https://en.wiktionary.org/wiki/thundercloud, https://en.wiktionary.org/wiki/thunderclouds