Wall clouds and inflow tails

Wall clouds & inflow tails (fulmen clouds)

A wall cloud is a lowering of cloud (rain-free) base at low levels of the storm. It forms in beneath the rain-free base of the thunderstorm, in the area of the most intense updraft. The wall cloud condenses as the cool air from the downdraft is pulled and mixed (entrained) into the storms inflow. As the cooler air drops the temperature of the inflow air, it cools and the moisture condenses, forming the wall cloud.

Wall clouds occasionally form on multicells, but are particularly frequent on supercell thundertorms.

Wall clouds come in many shapes and sizes, depending among other factors:

  • Type of the thunderstorm they are in.
  • Height of the rain-free base.
  • Relative humidity of inflow airmass.
  • Strength of the updraft.

Some wall clouds display strong rotation and may preceed the formation of a tornado.

An inflow tail is an extension of the wall cloud.

A beaver tail is a ….

The World Meteorological Organization defines fulmen clouds as: Bands of low clouds associated with a supercell severe convective storm (Cumulonimbus), arranged parallel to the low-level winds and moving into or towards the supercell.

These accessory clouds form on an inflow band into a supercell storm along the pseudo-warm front. The cloud elements move towards the updraft into the supercell, the base being at about the same height as the updraft base. Note that flumen are not attached to the murus wall cloud and the cloud base is higher than the wall cloud.

One particular type of inflow band cloud is the so-called ‘Beaver’s tail’. This is distinguished by a relatively broad, flat appearance suggestive of a beaver’s tail.

Wall clouds and inflow tails will be ??? in more detailed in the upcoming chapter SW 101: Supercells.


Short and stubby wall cloud on a high-based supercell. The cloud base is high, …




Wall cloud on an LP supercell.