Wind is returning, low and menacing at first (6)
I believe the answer is:
simoom
'wind' is the definition.
(simoom is a kind of wind)
'is returning low and menacing at first' is the wordplay.
'returning' is a reversal indicator.
'low' becomes 'moo' ('moo' can be a synonym of 'low').
'and' means one lot of letters go next to another.
'at first' indicates taking the first letters.
The first letter of 'menacing' is 'm'.
'is' back-to-front is 'si'.
'si'+'moo'+'m'='SIMOOM'
(Other definitions for simoom that I've seen before include "a blow" , "Violent sand-laden desert wind - so I'm Mo (anag)" .)