Wintry weather in south at the moment (4)
I believe the answer is:
snow
'wintry weather' is the definition.
(weather occurring in winter)
'south at the moment' is the wordplay.
'south' becomes 'S' (synonyms).
'at the moment' becomes 'now' (at the present moment).
's'+'now'='SNOW'
'in' acts as a link.
(Other definitions for snow that I've seen before include "Frozen precipitation" , "Vessel" , "Weather condition" , "novelist" , "that may arrive around Christmas time" .)