There are two kinds of shear: directional shear and speed shear. In
directional shear the wind direction changes as you ascend. This has the
effect of twisting the updraughts and downdraughts as they ascend /
descend.
Speed shear is when the wind speed changes with height (either higher or
lower) and also twists the updraught and downdraught motion.

(Perhaps too) simply put - doubtless i'll be corrected:
no or little shear: single cell (low CAPE)/ pulse (moderate CAPE) /
severe pulse thunderstorms (high CAPE) - downdraught swamps updraught
after 30 minutes or so and the cloud collapses. Showers in wintertime in
the UK are generally of the first type. Darwin (Australia) thunderstorms
are of the last type.

The UKMO mini-tornado (registered trade mark from Birmingham office) is
caused by the updraught spinning up in low shear conditions as it
tightens. Not that a T7 is a mini-tornado. But I digress (:

optimum shear(!): misocyclone, mesocyclone (supercell - high CAPE),
(mini-supercell - low CAPE) - rotation is set off within the cloud and
updraughts and downdraughts are out of each other's way and in
equilibrium. Tornadoes form in the boundary between updraught and
downdraught in these storm types. Misocyclones form in the UK in
wintertime and for mesocyclones think USA, Australia, China.....

high shear: multicell - updraughts and downdraughts are skewed and
daughter cell forms next to parent cell which eventually collapses.
Multicells form in all values of CAPE but the higher the better.

very high shear: nothing happens (clouds are shredded)

Keith (Southend) wrote:
Have I got this correct with regards the effect of wind shear with
thunder storms?


--
Les Crossan,
Wallsend, Tyne & Wear
54.95N 1.5W
Home of the Wallsend StormCam and the Backup USW FAQ -
www.uksevereweather.org.uk