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
RRS Discovery over the Christmas period the ship was blocked in by pack ice. A Norwegian whaler was met on December 29, which gifted the "Discovery" a further 50 tons of coal. On December 31 the ship was struck by a violent storm with winds of up to 70 mph (Force 11 on the Beaufort Scale). The ship was driven against the ice, while larger bergs were blown onto the ship by the wind. For eight hours the "Discovery" was repeatedly slammed into and onto thick ice and battered by bergs but MacKenzie was able to slowly work the ship offshore by