Then, a relative lull in the wet weather prevailed until the 21st when rainy, windy and cold weather returned.
(a relative lull in the wet weather; prevailed; until the 21st; T:Then) (rainy, windy and cold weather; returned; T:the 21st)
a relative lull in the wet weather rainy, windy and cold weather
prevailed returned
until the 21st T:Then
T:the 21st