Cloud PointField Guide

Cloud species — castellanus

Castellanus

Turrets that warn of afternoon thunderstorms

Written by Laurence WayneEntry No. 35Uncommon

Castellanus: Turrets that warn of afternoon thunderstorms
Plate XXXVPhotograph by Merikanto at fi.wikipedia, CC BY-SA 3.0.

Castellanus is a cloud species, not a genus: it describes clouds whose upper parts sprout small cumuliform turrets, crenellated like a castle's battlements and often lined up in rows from a common base. The turrets build where there is instability at cloud level, so rising bubbles of air push little towers up from the layer. The character shows best when viewed from the side, and the species spans cirrus, cirrocumulus, altocumulus and stratocumulus.

Worth knowing

  • Altocumulus castellanus is a classic forecaster's warning sign — those little morning turrets reveal instability in the mid-atmosphere, often signalling that thunderstorms will build later in the day.
Note

Still unsure it's the same cloud? Our app, Cloud Point— on iOS and Android — reads a photo and returns the likely type with altitude, useful when a formation is fading faster than you can look it up.

Test yourselfThree levels

Choose a difficulty

Castellanus clouds are recognised by…

  1. aSmall turrets or towers rising from a common base
  2. bA flat, smooth grey sheet
  3. cA single funnel reaching down
  4. dA ring of colour around the moon
Show answer

AnswerSmall turrets or towers rising from a common base

Their crenellated, castle-turret tops give the species its name.

Seeing altocumulus castellanus in the morning often warns of…

  1. aA calm, clear day ahead
  2. bMid-level instability and possible afternoon thunderstorms
  3. cIncoming fog by evening
  4. dA hard overnight frost
Show answer

AnswerMid-level instability and possible afternoon thunderstorms

The turrets reveal instability aloft that can build into thunderstorms later in the day.

Castellanus and floccus are both convective cloud species. How do you tell them apart?

  1. aCastellanus is always high, floccus always low
  2. bCastellanus turrets rise from a common base or line; floccus are isolated tufts, each with a ragged base often trailing virga
  3. cFloccus only ever appears at night
  4. dCastellanus is made of ice and floccus of water
Show answer

AnswerCastellanus turrets rise from a common base or line; floccus are isolated tufts, each with a ragged base often trailing virga

Castellanus shows turrets sharing a common base (often in rows); floccus are separate woolly tufts with ragged undersides — both signal instability aloft.

Nearby in the guide