Left on farm describing some forecasts (4,5)
I believe the answer is:
long-range
'describing some forecasts' is the definition.
(long-race forecast is a type of weather forecast)
'left on farm' is the wordplay.
'left' becomes 'l' (common abbreviation).
'farm' becomes 'grange' (grange is a kind of farm).
'l'+'on'+'grange'='LONG-RANGE'
(Other definitions for long-range that I've seen before include "(Of forecasts) relating to a time well into the future" , "Covering great distance, or looking further ahead" , "Involving a long period of time stretching into the future" , "referring to a weather forecast maybe" , "Acting over a distance" .)