Cumulonimbus and aviation at this altitude, updraughts with speeds that can exceed . Such an updraught speed corresponds to the wind speed of a small hurricane. The speed can even exceed . The maximum number in the Beaufort scale is 12 ("hurricane force" wind) and is assigned to wind speeds of 64 knots or greater. If the Beaufort scale were extended, these updraughts would have a Beaufort number of 14 "in the vertical direction". The turbulence is then "extreme" at this altitude. Moreover, the diameters of the updraught columns vary between 2 km (air mass thunderstorm) and 10 km (supercell thunderstorm). The height
Ode to the West Wind a prophet who does not only bring "black rain, and fire, and hail" (28), but who "will burst" (28) it. The "locks of the approaching storm" (23) are the messengers of this bursting: the "clouds". Shelley also mentions that when the West Wind blows, it seems to be singing a funeral song about the year coming to an end and that the sky covered with a dome of clouds looks like a "sepulchre", i.e., a burial chamber or grave for the dying year or the year which is coming to an end. Shelley in this canto "expands his vision from