Storm over old man is local nonsense (7)
I believe the answer is:
tornado
'storm' is the definition.
(tornado is a kind of storm)
'over old man is local nonsense' is the wordplay.
'over' is a reversal indicator.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'man' becomes 'dan'.
'is local nonsense' becomes 'rot' (I am not sure about this - if you are sure you should believe this answer much more).
'o'+'dan'+'rot'='odanrot'
'odanrot' back-to-front is 'TORNADO'.
Can you help me to learn more?
(Other definitions for tornado that I've seen before include "Tempest'" , "Funnel-shaped windstorm" , "Destructive windstorm" , "lot of wind" , "RAF fighter; whirlwind" .)