How to recognize upcoming storm? Look for Altocumulus castellanus

Štěpán Šubík

Among all of the Altocumulus cloud species, Altocumulus castellanus has the greatest impact on the weather forecast. So how to recognize it?

photo: Ralph W. lambrecht;
desc: Storm and tornado - bad weather.;
link: https://www.pexels.com/photo/lightning-and-tornado-hitting-village-1446076/;
licence: cc;

Altocumulus castellanus (Ac cas) is a mid-level cloud with its base from 2 km (6,500 ft) up to 6 km (20,000 ft). They are very similar to Stratocumulus castellanus and the main difference is that they look smaller and there is no precipitation connected to them.

photo: Bidgee;
desc: Altocumulus castellanus cloud type.;
link: https://commons.wikimedia.org/wiki/File:Altocumulus-Castellanus.jpg;
licence: cc;

But Altocumulus castellanus is a big help in predictions of incoming heavy showers or thunderstorms. Ac cas is created when a mid-level instability appears. If surface-based convection can connect to the mid-level instability, Ac cas can transform into Cumulonimbus clouds.

photo: Daniele.Brundu;
desc: Altocumulus castellanus cloud type.;
link: https://commons.wikimedia.org/wiki/File:Altocumulus_castellanus.jpg;
licence: cc;

Have you ever seen this phenomenon? Send us your photos!