Tornado without Funnel

Tornadoes can occur without funnel clouds, as shown in this example from NSSL. The dust cloud and cloud base above it were rotating, indicating a continuous cloud-to-ground vortex (tornado). The lack of a visible funnel can be related to several processes. Most likely, the pressure drop and lift in the tornado vortex was too weak to cool and condense a visible funnel; and/or the air below cloud base was too dry.