cl ones ▁▁ ▁Mes ocy cl ones ▁range ▁in ▁size ▁from ▁mes osc ale ▁beta ▁to ▁micro scale . ▁The ▁term ▁mes ocy clone ▁is ▁usually ▁reserved ▁for ▁mid - level ▁rot ations ▁within ▁severe ▁th under st orm s , ▁and ▁are ▁warm ▁core ▁cycl ones ▁driven ▁by ▁lat ent ▁heat ▁of ▁its ▁associated ▁th under st orm ▁activity . ▁ ▁T orn ado es ▁form ▁in ▁the ▁warm ▁sector ▁of ▁extr at rop ical ▁cycl ones ▁where ▁a ▁strong ▁upper ▁level ▁jet ▁stream ▁exists . ▁ ▁Mes ocy cl ones ▁are ▁believed ▁to ▁form ▁when ▁strong ▁changes ▁of ▁wind ▁speed ▁and / or ▁direction ▁with ▁height ▁(" wind ▁she ar ") ▁sets ▁parts ▁of ▁the ▁lower ▁part ▁of ▁the ▁atmosphere ▁spin ning ▁in ▁invisible ▁t ube - like ▁roll s . ▁The ▁con ve ct ive ▁upd raft ▁of ▁a ▁th under st orm ▁is ▁then ▁thought ▁to ▁draw ▁up ▁this ▁spin ning ▁air , ▁til ting ▁the ▁roll s ' ▁orientation ▁up ward ▁( from ▁parallel ▁to ▁the ▁ground ▁to ▁per pend icular ) ▁and ▁causing ▁the ▁entire ▁upd raft ▁to ▁rotate ▁as ▁a ▁vertical ▁column . ▁ ▁As ▁the ▁upd raft ▁rot ates , ▁it ▁may ▁form ▁what ▁is ▁known ▁as ▁a ▁wall ▁cloud . ▁The ▁wall ▁cloud ▁is ▁a ▁spin ning ▁layer ▁of ▁clouds ▁desc ending ▁from ▁the ▁mes ocy clone . ▁The ▁wall ▁cloud ▁tends ▁to ▁form ▁closer ▁to ▁the ▁center ▁of ▁the ▁mes ocy clone . ▁The ▁wall ▁clouds ▁do ▁not ▁necessarily ▁need ▁a ▁mes ocy