Figure 1-12.—Cumulus fractus cloud in a pannus layer.
The upper portion of the CB cell becomes broader
cirrus blow-off shield may extend well downstream of
and the top may become very indistinct as cirrus and
the CB cell. Then, the shield may thicken downward,
dense cirrus clouds develop from the ice crystals
becoming dense enough to blot out the shape of the sun
blowing downwind from the top portion of the cell. The
(fig. 1-13). Sometimes the dense cirrus blow-off (cirrus
Figure 1-13.—Dense cirrus blow-off (cirrus spissatus) from a thunderstorm.
1-13
