Note slippery patch on road: that is expected in December (8)
I believe the answer is:
solstice
'that is expected in december' is the definition.
(the winter solstice takes place in December)
'note slippery patch on road' is the wordplay.
'note' becomes 'sol' (I've seen this before).
'slippery patch' becomes 'ice' (ice is slippery).
'on' is a charade indicator (letters next to each other).
'road' becomes 'st'.
'ice' after 'st' is 'stice'.
'sol'+'stice'='SOLSTICE'
(Other definitions for solstice that I've seen before include "Time of year when sun is furthest from equator" , "Time of the longest or shortest day" , "Closest I come to time when sun is farthest from equator" , "When the sun is at its greatest distance from the celestial equator" , "When night and day are most unequal" .)