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
Francis Beaufort tomb may still be seen. His home in London, No. 51 Manchester Street, Westminster, is marked by an historic blue plaque noting his residency and achievements. During these early years of command, Beaufort developed the first versions of his Wind Force Scale and Weather Notation coding, which he was to use in his journals for the remainder of his life. From the circle representing a weather station, a staff (rather like the stem of a note in musical notation) extends, with one or more half or whole barbs. For example, a stave with 3½ barbs represents Beaufort seven on the