CUMULONIMBUS CLUSTER - TYPICAL APPEARANCE IN VERTICAL CROSS SECTIONS

by KNMI

Cumulonimbus Clusters in Warm Air can be found in a zone of warm and moist air in the lower levels and, in the initial stage, with dry air above. The WV image shows, in the initial stage of Cb development, a grey to dark grey area in which the first white Cb spots are visible.
05 August 1999/06.00 UTC - Meteosat WV image; position of vertical cross section indicated
05 August 1999/06.00 UTC - Vertical cross section; blue: relative humidity
The cross section shows a very moist layer below approximately 600 hPa

The airmass is conditionally unstable as a partial consequence of this humidity variation in the vertical. A cross section of ThetaE or ThetaW shows the height of this conditionally unstable layer.

05 August 1999/06.00 UTC - Vertical cross section; black: isentropes (ThetaW)
Convergence in the lower layer is visible in the surface wind field. A cross section is an ideal tool to detect these areas.
05 August 1999/18.00 UTC - Meteosat IR image; position of vertical cross section indicated
05 August 1999/18.00 UTC - Vertical cross section; magenta solid: divergence, magenta dashed: convergence