Cumulonimbus clouds rising over Puget Sound.   Photo courtesy M. D. Ruth

      It was hard to miss these towering clouds if you were out and about anywhere in Puget Sound today. These are culumonimbus clouds--the tallest of the clouds--showing its flattened anvil shape at its icy top. Because of the anvil shape, these clouds are more precisely described as cumulonimbus incus. If you watched long enough you might have seen the tops spread out in wisps, or hairs--turning them into cumulonimbus incus capillatus--and you into a Latin scholar! Incus means anvil; c apillatus means hai-like.
  These clouds are composed of water droplets in their lower portions and ice crystals in their upper portions. This was a cumulus congestus cloud (the big, cauliflower shaped ones) earlier in the day and rose through the troposphere under its own power --power produced within it as water molecules in the cloud condensed into droplets and released a tiny amount of heat (called latent heat). The cumulus congestus  continues to build until it reaches the troposphere/stratosphere boundary, called the tropopause, beyond which the air temperature begins to increase with altitude. When the cumulus congestus cloud hits this boundary, it can no longer rise, so it flattens out and assumes its distinctive anvil shape and its status as a cumulonimbus.
   Though cumulonimbus clouds are considered "low" clouds because their bases are low--just 2000 feet above the earth's surface. These majestic clouds are the tallest of the clouds, rising up to 40,000 feet above the earth.
   As you may remember, "nimbus" implies rain. And though Olympia was dry while this cloud was putting on its show this afternoon--some places to the northwest were getting hammered. With rain, maybe hail. Maybe drinks, too--but that's mixology, not meteorology.
  Cheers to the Clouds!